1,035

Accrued liabilities

16,335

16,382

Total current liabilities

46,988

40,559

69,707

61,147

Other long-term liabilities

255,053

264,704

2,055

1,897

Total liabilities

326,815

327,748

Commitments and contingencies

Stockholders' equity:

Common stock, $0.00001 par value; 75,000,000 shares authorized; 38,903,699 and 38,478,560 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively

Additional paid-in capital

295,744

289,454

Accumulated other comprehensive loss

(228)

(94)

Total stockholders' equity

(245,870)

(219,465)

49,647

69,896

Total liabilities and stockholders' equity

376,462

397,644

Convertible Preferred Stock

Stockholders' equity:

Convertible preferred stock, $0.00001 par value; 10,000,000 shares authorized and no shares issued and outstanding at March 31, 2018 and December 31, 2017.

[1]	The condensed balance sheet as of December 31, 2017 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017.

CONDENSED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	75,000,000	75,000,000
Common stock, shares issued	38,903,699	38,478,560
Common stock, shares outstanding	38,903,699	38,478,560
Convertible Preferred Stock
Convertible Preferred stock, par value	$ 0.00001	$ 0.00001
Convertible Preferred stock, shares authorized	10,000,000	10,000,000
Convertible Preferred stock, shares issued	0	0
Convertible Preferred stock, shares outstanding	0	0

CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Revenues	$ 14,184	$ 11,176
Revenues from related parties		477
Total revenues	14,184	11,653
Operating expenses:
Research and development	22,458	14,576
General and administrative	7,356	5,691
Total operating expenses	29,814	20,267
Loss from operations	(15,630)	(8,614)
Interest income	1,375	236
Other income (expense), net	(140)	120
Loss before provision for (benefit from) income taxes	(14,395)	(8,258)
Provision for (benefit from) income taxes	1,098	(1)
Net loss	$ (15,493)	$ (8,257)
Net loss per share, basic and diluted	$ (0.40)	$ (0.23)
Shares used to compute net loss per share, basic and diluted	38,647,878	36,538,869
Other comprehensive loss:
Changes in unrealized losses on short-term investments	$ (134)	$ (73)
Comprehensive loss	$ (15,627)	$ (8,330)

CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (15,493)	$ (8,257)
Adjustments to reconcile net loss to net cash used in operating activities:
Gain on disposal of property and equipment		(1)
Amortization of intangible assets	36
Depreciation and amortization	376	395
Amortization of premiums (accretion of discounts) on investments	(261)	203
Stock-based compensation expense	3,688	2,747
Deferred income taxes		1
Changes in operating assets and liabilities
Accounts receivable	10,058	1,946
Related party accounts receivable		99
Prepaid expenses and other current assets	(1,122)	(222)
Other assets	(20)	220
Accounts payable	1,115	(2,825)
Accrued liabilities, income tax payable and other long-term liabilities	1,145	(1,809)
Deferred revenue	(14,134)	(11,583)
Net cash used in operating activities	(14,612)	(19,086)
Cash flows from investing activities:
Purchases of property and equipment	(751)	(944)
Purchases of short-term investments	(48,132)	(40,094)
Maturities of short-term investments	25,500	40,250
Net cash used in investing activities	(23,383)	(788)
Cash flows from financing activities:
Proceeds from exercise of stock options	2,602	891
Net cash provided by financing activities	2,602	891
Net decrease in cash, cash equivalents and restricted cash	(35,393)	(18,983)
Cash, cash equivalents and restricted cash, beginning of period	178,465	105,562
Cash, cash equivalents and restricted cash, end of period	143,072	86,579
Supplemental disclosures of noncash investing and financing items:
Purchases of property and equipment in accounts payable and accrued liabilities	391	$ 230
ASC 606
Supplemental disclosures of noncash investing and financing items:
Non-cash adjustment to deferred revenue resulting from adoption of ASC 606	$ 10,912

Description of the Business	3 Months Ended
Description of the Business	Mar. 31, 2018
Disclosure Text Block [Abstract]
Description of the Business	1. Description of the Business CytomX Therapeutics, Inc. (the “Company”) is a clinical-stage, oncology-focused biopharmaceutical company with a vision of transforming lives with safer, more effective therapeutics. The Company is pioneering a novel class of investigational antibody therapeutics, based on its Probody™ therapeutic technology platform, for the treatment of cancer. The Probody therapeutic approach is designed to more specifically target antibody therapeutics to the tumor microenvironment and reduce drug activity in healthy tissue and in circulation. The Company is located in South San Francisco, California and was incorporated in the state of Delaware in September 2010.

Basis of Presentation and Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Basis of Presentation and Summary of Significant Accounting Policies

2. Basis of Presentation and Summary of Significant Accounting Policies

Basis of Presentation

The accompanying interim condensed financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding interim financial reporting.

Unaudited Interim Financial Information

The accompanying interim condensed financial statements and related disclosures are unaudited, have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for a fair statement of the results of operations for the periods presented.

Certain reclassifications have been made to prior period amounts to conform to the current period presentation. For the three months ended March 31, 2017, a reclassification of interest expense to interest income was made in the condensed statements of operations to conform to the current period presentation.

The condensed balance sheet data as of December 31, 2017 was derived from audited financial statements, but does not include all disclosures required by U.S. GAAP. The condensed results of operations for the three months ended March 31, 2018 are not necessarily indicative of the results to be expected for the full year or for any other future year or interim period. The accompanying condensed financial statements should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 filed with the SEC.

Use of Estimates

The preparation of the financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates.

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents.

Restricted Cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that sum to the total of the amounts shown in the statements of cash flows.

	As of March 31, 2018		As of December 31, 2017		As of March 31, 2017		As of December 31, 2016
Cash and cash equivalents	$	142,155	$	177,548	$	85,662	$	104,645
Restricted cash - non-current assets		917		917		917		917
Total	$	143,072	$	178,465	$	86,579	$	105,562

Restricted cash represents a standby letter of credit issued pursuant to an office lease entered in December 2015.

Comprehensive Income (Loss)

The Company’s unrealized gains and losses on short-term investments represent the only component of other comprehensive income (loss) that is excluded from the reported net loss.

Revenue Recognition

The Company adopted ASC Topic 606 effective January 1, 2018 on a modified retrospective basis. As such, the prior period amounts were not restated and continue to be presented in accordance with ASC Topic 605. For the Company’s accounting policy on revenue recognition prior to January 1, 2018, refer to the 2017 Form 10-K filed with the SEC on March 7, 2018. The policy disclosed in this Quarterly Report on Form 10-Q is the Company’s policy under ASC Topic 606, which was to be applied from January 1, 2018 forward.

The Company’s revenues are primarily derived through its license, research, development and commercialization agreements. The terms of these types of agreements may include (i) licenses for the Company’s technology or programs, (ii) research and development services, and (iii) services or obligations in connection with participation in research or steering committees. Payments to the Company under these arrangements typically include one or more of the following: nonrefundable upfront and license fees, research funding, milestone and other contingent payments to the Company for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of any commercialized products.

The Company recognizes revenue when the customer obtains control of the promised goods or services, in an amount that reflects the consideration which the Company has received or expects to receive in exchange for those goods or services.

The Company assesses whether the promises in its arrangements with customers are considered distinct performance obligations that should be accounted for separately. Judgment is required to determine whether the license to the Company’s intellectual property is distinct from the research and development services or participation on steering committees.

The transaction price in each arrangement is allocated to the identified performance obligations based on the standalone selling price (“SSP”) of each distinct performance obligation, which requires judgment. In instances where SSP is not directly observable, such as when a license or service is not sold separately, SSP is determined using information that may include market conditions and other observable inputs. Due to the early stage of the Company’s licensed technology, the license of such technology is typically combined with research and development services and steering committee participation as one performance obligation. In these cases, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

The Company’s collaboration and license agreements may include contingent payments related to specified research, development and regulatory milestones. Such payments are typically payable under the collaborations when the collaboration partner claims or selects a target, or initiates or advances a covered product candidate in preclinical or clinical development, upon submission for marketing approval of a covered product with regulatory authorities, or upon receipt of actual marketing approvals of a covered product or for additional indications. At each reporting date, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price by using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. Once determined, the transaction price is allocated to each performance obligation on a relative SSP basis. At the end of each subsequent reporting period, the Company re-evaluates the probability or achievement of each such milestone and any related constraint, and if necessary, adjusts its estimate of the overall transaction price.

The Company’s collaboration and license agreements may also include contingent payments related to sales-based milestones. Sales-based milestones are typically payable when annual sales of a covered product reach specified levels. Sales-based milestones are recognized at the later of when the associated performance obligation has been satisfied or when the sales occur. Unlike other contingency payments, such as regulatory milestones, sales-based milestones are not included in the transaction price based on estimates at the inception of the contract, but rather, are included when the sales or usage occur.

AbbVie Ireland Unlimited Company (“AbbVie”), one of the Company’s collaboration partners, entered into a license agreement with Seattle Genetics, Inc. (“SGEN”) to license certain intellectual property rights. As part of the Company’s collaboration agreement with AbbVie, the Company pays SGEN sublicense fees. These sublicense fees are treated as reductions of the transaction price and combined with the performance obligation to which they relate.

Contract Balances

Customer payments are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional.

Adopted Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. ASU 2014-09 replaced most existing revenue recognition guidance in U.S. GAAP. The standard permits the use of either the retrospective or cumulative effect transition method. Additionally, in March 2016, the FASB issued ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net), which clarifies the implementation guidance on principal versus agent considerations in ASU No. 2014-09. In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies certain aspects of identifying performance obligations and licensing implementation guidance. In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients, which relates to disclosures of remaining performance obligations, as well as other amendments to guidance on collectability, non-cash consideration and the presentation of sales and other similar taxes collected from customers. These standards (collectively Accounting Standard Codification Topic 606 (“ASC 606”) have the same effective date and transition date of January 1, 2018. The Company adopted ASC 606 on January 1, 2018, using the cumulative effect transition method. The Company elected to use the practical expedient for contract modifications whereby the aggregate effect of all modifications that occurred prior to the transition date can be reflected when identifying performance obligations and determining and allocating the transaction price.

The Company evaluated its contracts with customers under ASC 606. The impact of adopting ASC 606 on the Company’s results of operations, financial condition, and cash flows varies depending on the contract. The Company recorded adjustments upon the adoption of ASC 606 as a result of the different accounting treatment of its revenue agreements with respect to the inclusion of milestone payments in the initial transaction price and the method to be used to recognize upfront fees. Under the prior revenue recognition standard, milestone payments were recognized when earned and upfront fees were generally recognized as revenue over the research term on a straight-line basis if another method of revenue recognition did not more clearly match the pattern of delivery of goods or services to the customer. Under ASC 606, milestone payments are included in the initial transaction price when it is probable that a significant reversal of the milestone payment will not occur. In addition, the Company can no longer default to the straight-line method as the default method in recognizing revenue for goods or services delivered over time. As such, the amount and timing of revenue recognition for its collaboration agreements changed under the new revenue recognition standard. The impact of the adoption of ASC 606 was an increase in the balance of deferred revenue and an increase in the accumulated deficit balance of $10.9 million on January 1, 2018.

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed balance sheet line items (in thousands):

	As of March 31, 2018
	Balances Without the Adoption of ASC 606			Adjustments			As Reported
Liabilities
Income tax payable	$	1,154		$	(119	)	$	1,035
Deferred revenue - current		44,879			2,109			46,988
Deferred revenue - long-term		247,282			7,771			255,053
Stockholders' Equity
Accumulated deficit		(236,109	)		(9,761	)		(245,870	)

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed statement of operations line items (in thousands, except per share data):

	Three Months Ended March 31, 2018
	Balances Without the Adoption of ASC 606			Adjustments			As Reported
Revenue	$	12,626		$	1,558		$	14,184
Loss from Operations		(17,188	)		1,558			(15,630	)
Loss before provision for income taxes		(15,953	)		1,558			(14,395	)
Provision for income taxes		1,217			(119	)		1,098
Net loss		(17,170	)		1,677			(15,493	)
Net loss per share, basic and diluted		(0.44	)		0.04			(0.40	)

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed statement of cash flows line items (in thousands):

	Three Months Ended March 31, 2018
	Balances Without the Adoption of ASC 606			Adjustments			As Reported
Cash flows from operating activities:
Net loss	$	(17,170	)	$	1,677		$	(15,493	)
Changes in operating assets and liabilities:
Accrued liabilities, income tax payable and other long-term liabilities		1,264			(119	)		1,145
Deferred revenue		(12,576	)		(1,558	)		(14,134	)

In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The new standard provides clarification on the cash flow presentation and classification of certain transactions, including debt prepayment or extinguishment, settlement of certain debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of certain insurance claims and distributions received from equity method investees. The Company adopted this standard in its first quarter ended March 31, 2018. The adoption of this standard had no impact on the Company’s financial statements for the three months ended March 31, 2018.

In November 2016, the FASB issued ASU No. 2016-18, Restricted Cash, Statement of Cash Flows (Topic 230). ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The Company adopted this standard in its first quarter ended March 31, 2018. The Company has revised the presentation of restricted cash in its Statements of Cash Flows and provided the additional disclosures required under this standard.

In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting. This accounting standard update provides clarity when a change to terms or conditions of a share-based payment award must be accounted for as a modification. The new guidance requires modification accounting if the vesting condition, fair value or the award classification is not the same both before and after a change to the terms and conditions of the award. The Company adopted this standard on January 1, 2018. The adoption of this standard had no impact on the Company’s financial statements for the three months ended March 31, 2018.

Recent Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). Under ASU 2016-2, an entity will be required to recognize right-of-use assets and lease liabilities on its balance sheet and disclose key information about leasing arrangements. ASU 2016-02 offers specific accounting guidance for a lessee, a lessor and sale and leaseback transactions. Lessees and lessors are required to disclose qualitative and quantitative information about leasing arrangements to enable a user of the financial statements to assess the amount, timing and uncertainty of cash flows arising from leases. For public companies, ASU 2016-02 is effective for annual reporting periods beginning after December 15, 2018, including interim periods within that reporting period, and requires a modified retrospective adoption, with early adoption permitted. The Company plans to adopt this guidance beginning with its first quarter ending March 31, 2019. The Company is in the process of evaluating the future impact of ASU 2016-02 on its financial statements.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The new standard changes the impairment model for most financial assets and certain other instruments. Under the new standard, entities holding financial assets and net investment in leases that are not accounted for at fair value through net income are to be presented at the net amount expected to be collected. An allowance for credit losses will be a valuation account that will be deducted from the amortized cost basis of the financial asset to present the net carrying value at the amount expected to be collected on the financial asset. The new standard will be effective for the Company on January 1, 2020. The Company is currently assessing the impact of this new guidance.

In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The new standard simplifies the measurement of goodwill by eliminating the Step 2 impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount of that goodwill. The new guidance requires an entity to compare the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value. Additionally, an entity should consider income tax effects from any tax-deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. The new guidance becomes effective for goodwill impairment tests in fiscal years beginning after December 15, 2019, though early adoption is permitted. The Company is currently assessing the impact of this new guidance.

In February 2018, the FASB issued ASU No. 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. The amendments in this standard allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. The new standard will be effective for the Company on January 1, 2019.

In March 2018, the FASB issued ASU No. 2018-05, Income Taxes (topic 740): Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 (SEC Update). This standard adds various SEC paragraphs pursuant to the issuance of SEC Staff Accounting Bulletin No. 118, which clarifies the SEC Staff’s views on income tax accounting implications of the Tax Cuts and Jobs Act. It requires reporting of provisional amounts for specific income tax effects of the Act for which the accounting under ASC Topic 740 will be incomplete, but a reasonable estimate can be determined. Provision amounts for income tax effects of the Act for which a reasonable estimate cannot be determined, ASC Topic 740 should be applied based on provisions of the tax laws that were in effect immediately prior to the Act being enacted. Provisional amounts for income tax effects for which a reasonable estimate cannot be determined would be reported in the first reporting period in which a reasonable estimate can be determined. The Company continues to analyze the impact of the Tax Cuts and Jobs Act and reported provisional amounts for which it can reasonably estimate in the three months ended March 31, 2018. See Note 9, Income tax expense.

Fair Value Measurements and Short-Term Investments

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements and Short-Term Investments

3. Fair Value Measurements and Short-Term Investments

In accordance with ASC 820-10, Fair Value Measurements and Disclosures, the Company determines the fair value of financial and non-financial assets and liabilities using the fair value hierarchy, which establishes three levels of inputs that may be used to measure fair value, as follows:

•

Level I: Inputs which include quoted prices in active markets for identical assets and liabilities.

•

Level II: Inputs other than Level I that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

•

Level III: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

The carrying amounts of the Company’s financial instruments, including restricted cash, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities. The Company’s financial instruments consist of Level I and II assets. Level I assets consist primarily of highly liquid money market funds, some of which are included in restricted cash. The Company’s Level II assets consist of U.S. government bonds that are included in short-term investments.

The following tables set forth the fair value of the Company’s short-term investments subject to fair value measurements on a recurring basis and the level of inputs used in such measurements (in thousands):

		March 31, 2018
	Valuation Hierarchy	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Aggregate Fair Value
Assets
Money market funds	Level I	$	130,882	$	—	$	—		$	130,882
Restricted cash (money market funds)	Level I		917		—		—			917
U.S. Government bonds	Level I		219,524		—		(203	)		219,321
Total		$	351,323	$	—	$	(203	)	$	351,120

		December 31, 2017
	Valuation Hierarchy	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Aggregate Fair Value
Assets
Money market funds	Level I	$	164,440	$	—	$	—		$	164,440
Restricted cash (money market funds)	Level I		917		—		—			917
U.S. Government bonds	Level I		196,629		—		(67	)		196,562
Total		$	361,986	$	—	$	(67	)	$	361,919

As of March 31, 2018, no securities have contractual maturities of longer than one year.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Accrued Liabilities

3 Months Ended

Mar. 31, 2018

Accrued Liabilities Current [Abstract]

Accrued Liabilities

4. Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	March 31,		December 31,
	2018		2017
Research and clinical expenses	$	12,381	$	10,068
Payroll and related expenses		2,140		4,526
Legal and professional expenses		1,558		1,523
Other accrued expenses		256		265
Total	$	16,335	$	16,382

Research and Collaboration Agreements

3 Months Ended

Mar. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Research and Collaboration Agreements

5. Research and Collaboration Agreements

AbbVie Ireland Unlimited Company

In April 2016, the Company and AbbVie entered into two agreements, a CD71 Co-Development and Licensing Agreement (the “CD71 Agreement”) and a Discovery Collaboration and Licensing Agreement (the “Discovery Agreement” and together with the CD71 Agreement the “AbbVie Agreements”). Under the terms of the CD71 Agreement, the Company and AbbVie will co-develop a Probody Drug Conjugates (“PDC”) against CD71, with the Company responsible for pre-clinical and early clinical development. AbbVie will be responsible for later development and commercialization, with global late-stage development costs shared between the two companies. The Company will assume 35% of the net profits or net losses related to later development unless it opts-out. If the Company opts-out from participation of co-development of the CD71 PDC, AbbVie will have sole right and responsibility for the further development, manufacturing and commercialization of such CD71 PDC. AbbVie, at its sole discretion, may stop development of any CD71 PDC and terminate the CD71 Agreement if the Company does not meet certain preclinical research criteria by the applicable deadline. In such case, the Company and AbbVie may evaluate and approve an alternate CD71 PDC. If such alternate CD71 PDC is approved, then the Company and AbbVie will, in good faith, negotiate amendments to the timelines and, if necessary, the content in the research and development plan and budget and extensions to the deadlines to achieve defined success criteria.

Under the CD71 Agreement, the Company received an upfront payment of $20.0 million in April 2016, and is eligible to receive up to $470.0 million in development, regulatory and commercial milestone payments and royalties on ex-US sales in the high teens to low twenties if the Company participates in the co-development of the CD71 Licensed Product subject to a reduction in such royalties if the Company opts-out from the co-development of the CD71 PDC. The Company’s share of later stage co-development costs for each CD71 PDC are capped, provided that AbbVie may offset the Company’s co-development cost above the capped amounts from future payments such as milestone payments and royalties. In July 2017, the Company received a milestone payment of $14.0 million (net of the associated sublicense fee of $1.0 million) from AbbVie for achieving certain milestones required to be met to begin GLP toxicology studies under the CD71 Agreement.

Under the terms of the Discovery Agreement, AbbVie receives exclusive worldwide rights to develop and commercialize PDCs against up to two targets, one of which was selected in March 2017. The Company shall perform research services to discover the Probody therapeutics and create PDCs for the nominated collaboration targets. From that point, AbbVie shall have sole right and responsibility for development and commercialization of products comprising or containing such PDCs (“Discovery Licensed Products”).

Under the Discovery Agreement, the Company received an upfront payment of $10.0 million in April 2016 and may receive an additional payment upon the selection by AbbVie of the second target and the satisfaction of certain success criteria under the CD71 Agreement. AbbVie has not selected the second target, but the success criteria under the CD71 Agreement were met in September 2016. The Company is also eligible to receive up to $275.0 million in target nomination, development, regulatory and commercial milestone payments and royalties in the high single to low teens from commercial sales of any resulting PDCs.

The Company has determined that the CD71 and Discovery Agreements with AbbVie should be combined and evaluated as a single arrangement in determining revenue recognition, because both agreements were concurrently negotiated and executed.

The Company identified the following performance obligations at the inception of the AbbVie Agreements: (1) the research, development and commercialization license for CD71 Probody therapeutic, (2) the research services related to CD71 Probody therapeutic, (3) the obligation to participate in the CD71 Agreement joint research committee, (4) the research services related to the first discovery target (5) the research, development and commercialization license for the first discovery target, and (6) the obligation to participate in the Discovery Agreement joint research committee. The Company concluded that, at the inception of the agreement, AbbVie’s option for the second discovery target is not a material right and is therefore not a performance obligation.

The Company determined that the research, development and commercialization licenses for CD71 and discovery targets are not distinct from the Company’s respective research services and expertise. The Company considered factors such as novelty of the Probody therapeutic and PDC technology and lack of other parties’ expertise in this space, the Company’s rights to technology relating to a proprietary platform to enable the Probody therapeutic development and AbbVie’s contractual obligation to use the Company’s research services. The Company determined that the CD71 Agreement research, development and commercialization license, related research service and participation in the joint research committee were a combined performance obligation and were distinct from the Discovery Agreement research, development and commercialization license, related research service and participation in the joint research committee. Therefore, the Company concluded that there are two distinct performance obligations: CD71 Agreement performance obligation consisting of the CD71 Agreement research, development and commercialization license, related research service and participation in the joint research committee, and the Discovery Agreement performance obligation consisting of the Discovery Agreement research, development and commercialization license, related research service and participation in the joint research committee.

The transaction price consists of $30.0 million in upfront payments, $14.0 million milestone payment received (net of the associated sublicense fee of $1.0 million) less $4.2 million of estimated sublicense fees. The upfront payments under the AbbVie Agreements are allocated between the two performance obligations based on the estimated relative standalone selling prices. The $30.0 million of upfront payments is allocated $20.0 million to the CD71 Agreement, with the remaining $10.0 million allocated to the Discovery Agreement. The $14.0 million milestone payment received (net of the associated sublicense fee of $1.0 million) and estimated sublicense fees are allocated to the CD71 Agreement performance obligation as they are directly related to the development of the CD71 Probody therapeutic. The Company determined that the remaining potential milestone payments are probable of significant revenue reversal as their achievement is highly dependent on factors outside the Company’s control. Therefore, these payments have been fully constrained and are not included in the transaction price as of March 31, 2018. The Company recognizes the transaction price of $29.8 million allocated to the CD71 Agreement performance obligation using a cost-based input measure. In applying the cost-based input method of revenue recognition, the Company uses actual costs incurred relative to budgeted costs expected to be incurred for the combined performance obligation. These costs consist primarily of internal full-time employee (“FTE”) effort and third-party contract costs. Revenue is recognized based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligation over the five-year service period. As the Discovery Agreement performance obligation represents an obligation to continuously make the Company’s Probody therapeutic technology platform available to AbbVie, the initial transaction price of $10.0 million allocated to this performance obligation is recognized over the common measure of progress for the entire performance obligation over the estimated research service period of five years. The Company recognized revenue of $2.7 million and $1.4 million for the three months ended March 31, 2018 and 2017, respectively, related to the AbbVie Agreements. As of March 31, 2018 and December 31, 2017, deferred revenue related to the CD71 Agreement performance obligation was $17.0 million and $11.2 million, respectively, and deferred revenue related to the Discovery Agreement performance obligation was $6.2 million and $6.8 million, respectively. As of March 31, 2018, no amount was due from AbbVie under the AbbVie Agreement.

Amgen, Inc.

On September 29, 2017, the Company and Amgen, Inc. (“Amgen”) entered into a Collaboration and License Agreement (the “Amgen Agreement”). Pursuant to the Amgen Agreement, the Company received an upfront payment of $40.0 million in October 2017. Concurrent with the entry into the Amgen Agreement, the Company and Amgen entered into a Share Purchase Agreement (the “Purchase Agreement”) pursuant to which Amgen agreed to purchase 1,156,069 shares of the Company’s common stock, par value $0.00001 per share, at a price of $17.30 per share (calculated based on a 20-day volume-weighted average price), for total proceeds of $20.0 million, which the Company received on October 6, 2017, the closing date of the transaction. On the closing date, the Registration Rights Agreement (the “Registration Rights Agreement”) between the Company and Amgen went into effect. Pursuant to the Registration Rights Agreement, Amgen agreed not to dispose of any of the shares purchased during the six-month period following the closing date (the “lock-up period”) without the prior approval of a majority of the Company’s Board of Directors. The Company estimated a premium on the stock sold to Amgen of $0.5 million, which takes into account a discount due to the lack of marketability resulting from the six-month lockup period.

Under the terms of the Amgen Agreement, the Company and Amgen will co-develop a Probody T-cell engaging bi-specific therapeutic targeting EGFR (“EGFR Products”). The Company will be responsible for early-stage development of EGFR Products and all related costs (up to certain pre-set costs and certain limits based on clinical study size). Amgen will be responsible for late-stage development, commercialization, and all related costs of EGFR Products. Following early-stage development, the Company will have the right to elect to participate financially in the global co-development of EGFR Products with Amgen, during which the Company would bear certain of the worldwide development costs for EGFR Products and Amgen would bear the rest of such costs (the “EGFR Co-Development Option”). If the Company exercises its EGFR Co-Development Option, the Company will share in somewhat less than 50% of the profit and losses from sales of such EGFR Products in the U.S., subject to certain caps, offsets, and deferrals. If the Company chooses not to exercise its EGFR Co-Development Option, the Company will not bear any costs of later stage development. The Company is eligible to receive up to $455.0 million in development, regulatory, and commercial milestone payments for EGFR Products, and royalties in the low-double-digit to mid-teen percentage of worldwide commercial sales, provided that if the Company exercises its EGFR Co-Development option, it shall only receive royalties in the low-double-digit to mid-teen percentage of commercial sales outside of the United States.

Amgen also has the right to select a total of up to three targets, including the two additional targets discussed below. The Company and Amgen will collaborate in the research and development of Probody T-cell engaging bi-specifics products directed against such targets. Amgen has selected one such target (the “Amgen Other Product”). If Amgen exercises its option within a specified period of time, it can select two such additional targets (the “Amgen Option Products” and, together with the Amgen Other Product, the “Amgen Products”). Except with respect to preclinical activities to be conducted by CytomX, Amgen will be responsible, at its expense, for the development, manufacture, and commercialization of all Amgen Products. If Amgen exercises all of its options and advances all three of the Amgen Products, CytomX is eligible to receive up to $950.0 million in upfront, development, regulatory, and commercial milestones and tiered high single-digit to low-teen percentage royalties. The Company concluded that, at the inception of the agreement, Amgen’s option to select the two additional targets is not a material right and does not represent a performance obligation of the agreement.

At the initiation of the collaboration, CytomX had the option to select, from programs specified in the Amgen Agreement, an existing pre-clinical stage T-cell engaging bispecific product from the Amgen pre-clinical pipeline. In March 2018, CytomX selected the program. CytomX will be responsible, at its expense, for converting this program to a Probody T-cell engaging bispecific product, and thereafter, be responsible for development, manufacturing, and commercialization of the product (“CytomX Product”). Amgen is eligible to receive up to $203.0 million in development, regulatory, and commercial milestone payments for the CytomX Product, and tiered mid-single digit to low double-digit percentage royalties.

The Company considered the criteria for combining contracts in ASC 606 and determined that the Amgen Agreement and the Purchase Agreement should be combined into one contract. The Company accounted for the Amgen Agreement based on the fair values of the assets and services exchanged. The Company identified the following performance obligations at the inception of the Amgen Agreement: (1) the research, development and commercialization license, (2) the research and development services for the EGFR Products and the Amgen Other Product, and (3) the obligation to participate in the joint steering committee (“JSC”) and the joint research committee (“JRC”). The Company determined that research, development and commercialization license and the participation in the JSC and JRC are not distinct from the research and development services and therefore those performance obligations were combined into one combined performance obligation. The Amgen Other Products will be accounted for as a separate performance obligation from the EGFR Products as the nature of the services being performed is not the same and the value that Amgen can derive from one program is not dependent on the success of the other.

Concurrent with the execution of the Amgen Agreement, the Company entered into a sublicense agreement whereby the Company granted Amgen a sublicense of its rights to one patent family that it co-owns with the Regents of the University of California, acting through its Santa Barbara campus (“UCSB”), that is exclusively licensed to us under the UCSB Agreement covering Probody antibodies and other pro-proteins in the fields of therapeutics, in vivo diagnostics and prophylactics. This sublicense was incremental to the patents, patent applications and know-how covering T-cell engaging bispecific Probody molecules that were developed and owned by the Company and licensed to Amgen. Under the UCSB Agreement, the Company is obligated to make a royalty payment to UCSB equal to 15% of certain sublicense revenue payments owed to or received by the Company. The Company determined that the calculation of the sublicense fee is not specifically addressed in the sublicense agreement when the Company simultaneously licenses the UCSB technology along with the technology the Company has developed internally. As of December 31, 2017, the Company recorded a liability of $2.1 million, which represents the Company’s best estimate of the amount to be remitted to UCSB. As of March 31, 2018, the Company determined that the estimated liability of $2.1 million is still appropriate.

The total transaction price of $51.2 million, consisting of the $40.0 million upfront payment, an estimated fair value of $10.7 million for the CytomX Product and $0.5 million of premium on the sale of the Company’s equity, was allocated between two performance obligations based on the relative standalone selling price of each performance obligation. To determine the standalone selling price, the Company used the discounted cash flow method by calculating risk-adjusted net present values of estimated cash flows. The Company determined that the remaining potential milestone payments are probable of significant revenue reversal as their achievement is highly dependent on factors outside the Company’s control. Therefore, these payments have been fully constrained and are not included in the transaction price as of March 31, 2018. The Company recognizes the transaction price of $45.8 million allocated to the EGFR Products performance obligation using a cost-based input measure. In applying the cost-based input method of revenue recognition, the Company uses actual costs incurred relative to budgeted costs expected to be incurred for the combined performance obligation. These costs consist primarily of internal FTE effort and third-party contract costs. Revenue is recognized based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligation over the six-year service period. As the Amgen Other Product performance obligation represents an obligation to continuously make the Probody therapeutic technology platform available to Amgen, the initial transaction price of $4.7 million allocated to this performance obligation is recognized over the common measure of progress for the entire performance obligation over the estimated research service period of six years.

The Company recognized revenue of $1.3 million for the three months ended March 31, 2018, related to the Amgen Agreement. As of March 31, 2018 and December 31, 2017, deferred revenue related to the EGFR Products performance obligation was $43.7 million and $45.3 million, respectively. As of March 31, 2018 and December 31, 2017, deferred revenue related to the Amgen Other Products performance obligation was $4.4 million and $4.6 million, respectively. As of March 31, 2018, no amount was due from Amgen under the Amgen Agreement.

Bristol-Myers Squibb Company

On May 23, 2014, the Company and Bristol-Myers Squibb Company (“BMS”) entered into a Collaboration and License Agreement (the “BMS Agreement”) to discover and develop compounds for use in human therapeutics aimed at multiple immuno-oncology targets using the Company’s Probody therapeutic technology. The effective date of the BMS Agreement was July 7, 2014.

Under the terms of the BMS Agreement, the Company granted BMS exclusive worldwide rights to develop and commercialize Probody therapeutics for up to four oncology targets. BMS had additional rights to substitute up to two collaboration targets within three years of the effective date of the BMS Agreement. These rights expired in May 2017. Each collaboration target has a two-year research term and the two additional targets must be nominated by BMS within five years of the effective date of the BMS Agreement. The research term for each collaboration target can be extended in one-year increments up to three times.

Pursuant to the BMS Agreement, the financial consideration from BMS was comprised of an upfront payment of $50.0 million and was initially entitled to receive contingent payments of up to an aggregate of $1,217.0 million as follows: (i) up to $25.0 million for additional targets; (ii) up to $114.0 million in development milestone payments per research target program or up to $456.0 million if the maximum of four research targets are selected; (iii) up to $124.0 million in milestone payments for the first commercial sale in various territories for up to three indications per research target program or up to $496.0 million if the maximum of four research targets are selected, and (iv) up to $60.0 million in sales milestones payments per research target program or up to $240.0 million if maximum of four research targets are selected. The Company is entitled to royalty payments in the mid-single digits to low double-digit percentages from potential future sales. The Company will also receive research and development service fees based on a prescribed FTE rate that is capped.

The Company identified the following performance obligations at the inception of the BMS Agreement: (1) the exclusive research, development and commercialization license, (2) the research and development services and (3) the obligation to participate in the joint research committee. The Company determined that the license, the Company’s research services and expertise related to the development of the product candidates should be combined with the research services and participation in the joint research committee as one combined performance obligation. The Company concluded that, at the inception of the agreement, BMS’ options for the third and fourth targets were not material rights and not performance obligations. As such, each option was accounted for as a separate arrangement upon exercise. Additionally, the Company considered whether the services performed for each target should be considered separate performance obligations and concluded that all targets should be accounted for as one combined performance obligation.

The Company received an upfront payment of $50.0 million from BMS in July 2014. In January and December 2016, BMS selected the third and fourth targets, respectively, and paid the Company $10.0 million and $15.0 million, respectively, pursuant to the terms of the BMS Agreement. In December 2016, BMS selected a clinical candidate pursuant to the BMS Agreement, which triggered a $2.0 million pre-clinical milestone payment to the Company. In November 2017, the Company recognized a $10.0 million milestone payment from BMS upon approval of the investigational new drug application for the CTLA-4-directed Probody therapeutic.

On March 17, 2017, the Company and BMS entered into Amendment Number 1 to Extend Collaboration and License Agreement (the “Amendment”). The Amendment grants BMS exclusive worldwide rights to develop and commercialize Probody therapeutics for up to six additional oncology targets and two non-oncology targets. The effective date of the Amendment was April 25, 2017 (“Amendment Effective Date”).

Under the terms of the Amendment, the Company will continue to collaborate with BMS to discover and conduct preclinical development of Probody therapeutics against targets selected by BMS under the terms of the Amendment.

Pursuant to the Amendment, the financial consideration from BMS was comprised of an upfront payment of $200.0 million and the Company will be eligible to receive up to an aggregate of $3,586.0 million as follows: (i) up to $116.0 million in development milestone payments per target or up to $928.0 million if the maximum of eight targets are selected for the first product modality; (ii) up to $124.0 million in milestone payments for the first commercial sale in various territories for up to three indications per target program or up to $992.0 million if the maximum of eight targets are selected for the first product modality; (iii) up to $60.0 million in sales milestone payments per target or up to $480.0 million if maximum of eight targets are selected for the first product modality; and (iv) up to $56.3 million in development milestone payments or up to $450.0 million if the maximum of eight targets are selected for the second product modality; (v) up to $62.0 million in milestone payments for the first commercial sale in various territories for up to three indications per target program or up to $496.0 million if the maximum of eight targets are selected for the second product modality; (iii) up to $30.0 million in sales milestone payments per target or up to $240.0 million if maximum of eight targets are selected for the second product modality. The Company is also entitled to tiered mid-single to low double-digit percentage royalties from potential future sales. The Amendment does not change the term of the BMS’ royalty obligation under the BMS Agreement. BMS’ royalty obligation continues on a licensed product-by licensed-product basis until the later of (i) the expiration of the last claim of the licensed patents covering the licensed products in the country, (ii) the twelfth anniversary of the first commercial sale of a licensed product in a country, or (iii) the expiration of any applicable regulatory, pediatric, orphan drug or data exclusivity with respect to such product.

The initial transaction price is $272.8 million consisting of the upfront fees of $250.0 million, research and development service fees of $10.8 million and milestone payments received to date of $12.0 million. The Company determined that the remaining potential milestone payments are probable of significant revenue reversal as their achievement is highly dependent on factors outside the Company’s control. Therefore, these payments have been fully constrained and are not included in the transaction price as of March 31, 2018. The BMS Agreement represents an obligation to continuously make the Probody therapeutic technology platform available to BMS. Therefore, the initial transaction price is recognized over the estimated research service period which ends on April 25, 2023.

The Company recognized revenue of $8.2 million and $3.3 million for the three months ended March 31, 2018 and 2017, respectively. As of March 31, 2018 and December 31, 2017, deferred revenue relating to the BMS Agreement was $230.0 million and $235.0 million, respectively. The amount due from BMS under the BMS Agreement was $67,000 and $10.1 million as of March 31, 2018 and December 31, 2017, respectively.

ImmunoGen, Inc.

In January 2014, the Company and ImmunoGen, Inc. (“ImmunoGen”) entered into the Research Collaboration Agreement (the “ImmunoGen Agreement”). The ImmunoGen Agreement provides the Company with the right to use ImmunoGen’s Antibody Drug Conjugate (“ADC”) technology in combination with the Company’s Probody therapeutic technology to create a PDC directed at one specified target under a research license, and to subsequently obtain an exclusive, worldwide development and commercialization license to use ImmunoGen’s ADC technology to develop and commercialize such PDCs. The Company made no upfront cash payment in connection with the execution of the agreement. Instead, the Company provided ImmunoGen with the rights to CytomX’s Probody therapeutic technology to create PDCs directed at two targets under the research license and to subsequently obtain exclusive, worldwide development and commercialization licenses to develop and commercialize such PDCs. In February 2017, ImmunoGen exercised its option to obtain a development and commercialization license for one of the two targets. ImmunoGen discontinued one of the two programs being developed under the ImmunoGen Agreement in July 2017 and substitution rights for this program terminated in February 2017. The Company recognized the remaining deferred revenue related to the discontinued program upon the termination of the program. ImmunoGen continues research work on the second collaboration target.

Under the terms of the agreement, both the Company and ImmunoGen are required to perform research activities on behalf of the other party for no monetary consideration. The research activities for a particular target will last until January 2018 unless they are terminated by one of the parties or when a development and commercialization license is obtained with respect to that target. This arrangement was extended to June 2018, as discussed below. Each party is solely responsible for the development, manufacturing and commercialization of any products resulting from the exclusive development and commercialization license obtained by such party under the agreement. Each party may be liable to pay annual maintenance fees to the other party if the licensed product candidate covered under each development and commercialization license has not progressed to the clinical stage of development within six years of the exercise of the development and commercialization license.

In consideration for the exclusive development and commercialization license that may be obtained by ImmunoGen, the Company is entitled to receive up to $30.0 million in development and regulatory milestone payments per the research program target, up to $50.0 million in sales milestone payments per target and royalties in the mid-single digits on the commercial sales of any resulting product. For the development and commercialization license that may be obtained by the Company, ImmunoGen is entitled to receive up to $60.0 million in development and regulatory milestone payments, up to $100.0 million in sales milestone payments and royalties in the mid to high single digits on the commercial sales of any resulting product. In August 2017, the Company made a milestone payment of $1.0 million to ImmunoGen for the first patient dosing with CX-2009.

The Company accounted for the ImmunoGen Agreement based on the fair value of the assets and services exchanged. The Company identified the following performance obligations at the inception of the ImmunoGen Agreement: (1) the research license, (2) the research services, (3) the obligation to participate in the joint research committee, (4) the exclusive research, development and commercialization license and (5) the obligation to provide future technology improvements, when available. The Company determined that the research license, participation in the joint steering committee, the research services, and the technology improvements are not distinct from the development and commercialization license and therefore those performance obligations were combined into one combined performance obligation. The Company considered factors such the limited economic benefits to ImmunoGen if the development and commercialization license is not obtained and the lack of sublicensing rights in the research license.

The estimated total fair value of the consideration of $13.2 million was recorded as deferred revenue at the inception of the agreement. In December 2017, the Company entered into a license agreement with ImmunoGen (the “ImmunoGen Amendment”) pursuant to ImmunoGen’s exercise of its option to obtain a development and commercialization license for the second research program target under the ImmunoGen Agreement. The ImmunoGen Amendment extended the Company’s obligation to provide research services from January 8, 2018 to June 30, 2018. The fair value of the consideration for the combined performance obligation is being recognized as revenue over the research period ending on June 30, 2018.

The estimated fair value of assets and services received was also $13.2 million, of which $12.7 million was allocated to the licenses received and was charged to research and development expense, with the remaining amount of $0.5 million was allocated to the research services, joint research committee participation and technology improvements, which will be expensed over the period of services to be provided.

The Company recognized revenue of $0.7 million and $6.5 million for this target for the three months ended March 31, 2018 and 2017, respectively. As of March 31, 2018 and December 31, 2017, deferred revenue relating to the ImmunoGen Agreement was $0.7 million and $0.7 million, respectively. As of both March 31, 2018 and December 31, 2017, no amount was due from ImmunoGen under the ImmunoGen Agreement.

MD Anderson

In November 2015, the Company entered into a research collaboration agreement with MD Anderson to research Probody-enabled chimeric antigen receptor killer (CAR-NK) cell therapies, known as ProCAR-NK cell therapies. Under this collaboration, MD Anderson will use the Company’s Probody technology to conduct research of ProCAR-NK cell therapies against certain targets selected by the Company in cancer immunotherapy. Under the research collaboration agreement, the Company has the right to exercise an option, during the option period expiring on November 2, 2019 and upon payment of an option exercise fee, to negotiate and acquire a worldwide, exclusive, sublicensable license from MD Anderson for development and commercialization of products directed against any of the selected targets. The research collaboration agreement will continue in effect until the earlier of (i) the date that the Company exercises the option to acquire the license from MD Anderson and (ii) the expiration of the option period. The expenses related to this agreement was not material for the financial statements for the three months ended March 31, 2018 and 2017.

Pfizer Inc.

In May 2013, the Company and Pfizer Inc. (“Pfizer”) entered into a Research Collaboration, Option and License Agreement (the “Pfizer Agreement”) to collaborate on the discovery and preclinical research activities related to Probody therapeutics, and PDCs for research project targets nominated by Pfizer. Pfizer nominated two research targets in 2013 and, pursuant to the Pfizer Agreement, had the option of nominating two additional research targets. In December 2014, Pfizer selected an additional research target and paid the Company $1.5 million. The option to select a fourth target lapsed in May 2016. Pfizer has discontinued the epidermal growth factor receptor (“EGFR”) program and decided to terminate the remaining two targets in February and March 2018. On March 6, 2018, Pfizer notified the Company that it was terminating the Pfizer Agreement. As such, the Company had no further performance obligations under this agreement following March 6, 2018 and recognized the remaining deferred revenue of $1.1 million.

Pursuant to the Pfizer Agreement, the Company received an upfront payment of $6.0 million and research and development service fees based on a prescribed FTE rate per year that is capped. The Company identified the following performance obligations at the inception of the Pfizer Agreement: (1) the research license, (2) the research services and (3) the obligation to participate in the joint research committee. The Company determined that the research license was not distinct from the research services and participation in the joint research committee due to the specialized nature of the research services to be provided by the Company, and accordingly, this deliverable was combined with the research services and participation in the joint research committee as a combined performance obligation. The Company concluded that, at the inception of the agreement, Pfizer’s options to obtain an exclusive development and commercialization license for each research project target do not represent a material right and are not performance obligations.

As the combined performance obligation represented an obligation to continuously make the Probody therapeutic technology platform available to Pfizer, the initial transaction price was recognized over the common measure of progress for the entire performance obligation over the estimated research service period of five and a half years.

The Company recognized revenue of $1.4 million and $0.5 million for the three months ended March 31, 2018 and 2017, respectively. As of March 31, 2018 and December 31, 2017, deferred revenue relating to the Pfizer Agreement was $0 and $1.6 million, respectively. As of March 31, 2018 and December 31, 2017, the amount due from Pfizer under the Pfizer Agreement was $14,000 and $13,000, respectively.

Contract Liabilities

The following table presents changes in the Company’s total contract assets and liabilities during the three months ended March 31, 2018 (in thousands):

Balance at

Beginning of

Period

Additions

Deductions

Balance at

End

of Period

Contract liabilities:

Deferred revenue

305,263

10,912

(14,134

)

302,041

Additions of $10.9 million represent the ASC 606 adoption adjustment. Deductions of $14.1 million represents revenue recognized in the three months ended March 31, 2018 that was included in the contract liability balance at the beginning of the period.

The Company estimates that the $302.0 million of deferred revenue related to the following contracts as of March 31, 2018 to be recognized as revenue as set forth below. However, the timing of revenue recognition could differ from the estimates depending on facts and circumstances impacting the various contracts, including progress of research and development, resources assigned to the contracts by the Company or its collaboration partners or other factors outside of the Company’s control.

•

The $17.0 million of deferred revenue related to the AbbVie CD71 Agreement as of March 31, 2018 is expected to be recognized based on actual FTE effort over the next three years until April 2021.

•

The $6.2 million of deferred revenue related to the Discovery Agreement as of March 31, 2018 is expected to be recognized ratably over the next three years until April 2021.

•

The $43.7 million of deferred revenue related to the Amgen EGFR Products as of March 31, 2018 is expected to be recognized based on actual FTE effort over the next five years until September 2023.

•

The $4.4 million of deferred revenue related to the Amgen Other Products as of March 31, 2018 is expected to be recognized ratably over the next five years until September 2023.

•

The $230.0 million of deferred revenue related to the BMS Agreement is expected to be recognized ratably over the next seven years until April 2025.

•

The $0.7 million of deferred revenue related to the ImmunoGen Agreement is expected to be recognized ratably over next three months until June 2018.

License Agreement	3 Months Ended
License Agreement	Mar. 31, 2018
Research And Development [Abstract]
License Agreement	6. License Agreement The Company has an exclusive, worldwide license agreement (the “UCSB Agreement”) with UCSB, relating to the use of certain patents and technology relating to its core technology, including its therapeutic antibodies, and to certain patent rights the Company co-owns with UCSB covering Probody antibodies and other pro-proteins. Pursuant to the UCSB Agreement, the Company is obligated to (i) make royalty payments to UCSB on net sales of its products covered under the agreement, subject to annual minimum amounts, (ii) make milestone payments to UCSB upon the occurrence of certain events, (iii) make a milestone payment to UCSB upon occurrence of an IPO or change of control, and (iv) reimburse UCSB for prosecution and maintenance of the licensed patents. If the Company sublicenses its rights under the UCSB Agreement, it is obligated to pay UCSB a percentage of the total sublicense revenue received, which total amount would be first reduced by the aggregate amount of certain research and development related expenses incurred by the Company and other permitted deductions. In 2013, the Company amended the UCSB Agreement to reduce certain amounts due to UCSB upon receipt by the Company of upfront payments, milestone payments and royalties from sublicensees. In exchange for this amendment, the Company issued to UCSB 157,332 shares of common stock. The UCSB Agreement, as amended, will remain in effect until the expiration or abandonment of the last to expire of the licensed patents. During the three months ended March 31, 2018 and 2017, the Company incurred expenses of $11,000 and $0.2 million, respectively, to UCSB under the provisions of the UCSB Agreement. Royalty obligations The Company has annual minimum royalty obligations of $150,000 under the terms of certain exclusive licensed patent rights. The royalty obligations are cancellable any time by giving notice to the licensor, with the termination being effective 60 days after giving notice.

Stock-Based Compensation

3 Months Ended

Mar. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

7. Stock-Based Compensation

Stock Options

Activities under the Company’s stock option plans for the three months ended March 31, 2018 were as follows:

	Options Outstanding
	Number of Options			Weighted- Average Exercise Price Per Share
Balances at December 31, 2017		6,503,458		$	8.157
Options granted		1,261,400			26.215
Options exercised		(425,139	)		6.122
Option forfeited/expired		(33,764	)		15.491
Balances at March 31, 2018		7,305,955		$	11.360
Options exercisable at March 31, 2018		3,600,751		$	5.957

Stock-based Compensation

Total stock-based compensation recorded related to options granted to employees and non-employees and employee stock purchase plan was as follows (in thousands):

	Three Months Ended
	March 31,
	2018		2017
Stock-based compensation expense:
Research and development	$	1,808	$	1,227
General and administrative		1,880		1,520
Total stock-based compensation expense	$	3,688	$	2,747

Net Loss Per Share

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Net Loss Per Share

8. Net Loss Per Share

The following weighted-average outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented, because including them would have been anti-dilutive:

	Three Months Ended
	March 31,
	2018		2017
Options to purchase common stock		7,199,679		7,055,207
Total		7,199,679		7,055,207

Income Tax Expense	3 Months Ended
Income Tax Expense	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Tax Expense	9. Income Tax Expense The Company recorded a provision for income taxes of $1.1 million during the three months ended March 31, 2018. The income tax expense was generated as a result of a timing difference in the recognition of revenue between tax and U.S. GAAP purposes, primarily related to the upfront payment received from the BMS Agreement. The recognition of this revenue for tax purposes resulted in taxable income and therefore, tax expense. The Company’s effective tax rate was -7.63% and 0.0% for the three months ended March 31, 2018 and 2017, respectively. Income tax expense for the three months ended March 31, 2018 was accrued based on the newly-enacted statutory federal tax rate of 21%, which was effective for tax years starting January 1, 2018. The Company maintains a full valuation allowance against its net deferred tax assets due to the Company’s history of losses as of March 31, 2018. On December 22, 2017, the Tax Cuts and Jobs Act (“Tax Act”) of 2017 was signed into law making significant changes to the Internal Revenue Code. The Tax Act contains significant changes to corporate income tax, including among other things, a reduction to the corporate income tax rate from a top marginal rate of 35% to a flat rate of 21%. Since further guidance, interpretations and rulings are expected in the 12 months following enactment, the Company has made certain provisional estimates, as permitted by SAB 118 and continues to analyze the impact of the Tax Act. As of March 31, 2018, the Company has not completed its accounting for all of the effects of the Tax Act due to pending guidance, interpretations and rulings to be issued. The Company did not make any adjustments during the three months ended March 31, 2018 to the tax amounts recorded during the year ended December 31, 2017. As the Company collects and prepares the necessary data and obtains further guidance or interpretation of the Tax Act, it may make adjustments to the provisional amounts that it has recorded that may materially impact the provision for income taxes in the period in which the adjustments are made. The Company will complete its accounting analysis when the interpretations, guidance and rulings are finalized by the various tax and standard-setting bodies, which is expected by the end of December 2018.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Basis of Presentation

Unaudited Interim Financial Information

Use of Estimates

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents.

Restricted Cash

	As of March 31, 2018		As of December 31, 2017		As of March 31, 2017		As of December 31, 2016
Cash and cash equivalents	$	142,155	$	177,548	$	85,662	$	104,645
Restricted cash - non-current assets		917		917		917		917
Total	$	143,072	$	178,465	$	86,579	$	105,562

Restricted cash represents a standby letter of credit issued pursuant to an office lease entered in December 2015.

Comprehensive Income (Loss)

The Company’s unrealized gains and losses on short-term investments represent the only component of other comprehensive income (loss) that is excluded from the reported net loss.

Revenue Recognition

Contract Balances

Adopted Accounting Pronouncements and Recent Accounting Pronouncements

Adopted Accounting Pronouncements

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed balance sheet line items (in thousands):

	As of March 31, 2018
	Balances Without the Adoption of ASC 606			Adjustments			As Reported
Liabilities
Income tax payable	$	1,154		$	(119	)	$	1,035
Deferred revenue - current		44,879			2,109			46,988
Deferred revenue - long-term		247,282			7,771			255,053
Stockholders' Equity
Accumulated deficit		(236,109	)		(9,761	)		(245,870	)

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed statement of operations line items (in thousands, except per share data):

	Three Months Ended March 31, 2018
	Balances Without the Adoption of ASC 606			Adjustments			As Reported
Revenue	$	12,626		$	1,558		$	14,184
Loss from Operations		(17,188	)		1,558			(15,630	)
Loss before provision for income taxes		(15,953	)		1,558			(14,395	)
Provision for income taxes		1,217			(119	)		1,098
Net loss		(17,170	)		1,677			(15,493	)
Net loss per share, basic and diluted		(0.44	)		0.04			(0.40	)

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed statement of cash flows line items (in thousands):

	Three Months Ended March 31, 2018
	Balances Without the Adoption of ASC 606			Adjustments			As Reported
Cash flows from operating activities:
Net loss	$	(17,170	)	$	1,677		$	(15,493	)
Changes in operating assets and liabilities:
Accrued liabilities, income tax payable and other long-term liabilities		1,264			(119	)		1,145
Deferred revenue		(12,576	)		(1,558	)		(14,134	)

Recent Accounting Pronouncements

Basis of Presentation and Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2018

Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash

	As of March 31, 2018		As of December 31, 2017		As of March 31, 2017		As of December 31, 2016
Cash and cash equivalents	$	142,155	$	177,548	$	85,662	$	104,645
Restricted cash - non-current assets		917		917		917		917
Total	$	143,072	$	178,465	$	86,579	$	105,562

ASC 606

Summary Impact of Adopting ASC 606 on Select Unaudited Financial Statement Line Items

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed balance sheet line items (in thousands):

	As of March 31, 2018
	Balances Without the Adoption of ASC 606			Adjustments			As Reported
Liabilities
Income tax payable	$	1,154		$	(119	)	$	1,035
Deferred revenue - current		44,879			2,109			46,988
Deferred revenue - long-term		247,282			7,771			255,053
Stockholders' Equity
Accumulated deficit		(236,109	)		(9,761	)		(245,870	)

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed statement of operations line items (in thousands, except per share data):

	Three Months Ended March 31, 2018
	Balances Without the Adoption of ASC 606			Adjustments			As Reported
Revenue	$	12,626		$	1,558		$	14,184
Loss from Operations		(17,188	)		1,558			(15,630	)
Loss before provision for income taxes		(15,953	)		1,558			(14,395	)
Provision for income taxes		1,217			(119	)		1,098
Net loss		(17,170	)		1,677			(15,493	)
Net loss per share, basic and diluted		(0.44	)		0.04			(0.40	)

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed statement of cash flows line items (in thousands):

	Three Months Ended March 31, 2018
	Balances Without the Adoption of ASC 606			Adjustments			As Reported
Cash flows from operating activities:
Net loss	$	(17,170	)	$	1,677		$	(15,493	)
Changes in operating assets and liabilities:
Accrued liabilities, income tax payable and other long-term liabilities		1,264			(119	)		1,145
Deferred revenue		(12,576	)		(1,558	)		(14,134	)

Fair Value Measurements and Short-Term Investments (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of Short-Term Investments Subject to Fair Value Measurements on a Recurring Basis

		March 31, 2018
	Valuation Hierarchy	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Aggregate Fair Value
Assets
Money market funds	Level I	$	130,882	$	—	$	—		$	130,882
Restricted cash (money market funds)	Level I		917		—		—			917
U.S. Government bonds	Level I		219,524		—		(203	)		219,321
Total		$	351,323	$	—	$	(203	)	$	351,120

		December 31, 2017
	Valuation Hierarchy	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Aggregate Fair Value
Assets
Money market funds	Level I	$	164,440	$	—	$	—		$	164,440
Restricted cash (money market funds)	Level I		917		—		—			917
U.S. Government bonds	Level I		196,629		—		(67	)		196,562
Total		$	361,986	$	—	$	(67	)	$	361,919

Accrued Liabilities (Tables)

3 Months Ended

Mar. 31, 2018

Accrued Liabilities Current [Abstract]

Schedule of Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	March 31,		December 31,
	2018		2017
Research and clinical expenses	$	12,381	$	10,068
Payroll and related expenses		2,140		4,526
Legal and professional expenses		1,558		1,523
Other accrued expenses		256		265
Total	$	16,335	$	16,382

Research and Collaboration Agreements (Tables)

3 Months Ended

Mar. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Summary of Contracts Assets and Liabilities

The following table presents changes in the Company’s total contract assets and liabilities during the three months ended March 31, 2018 (in thousands):

Balance at

Beginning of

Period

Additions

Deductions

Balance at

End

of Period

Contract liabilities:

Deferred revenue

305,263

10,912

(14,134

)

302,041

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Activities Under Company's Stock Option Plans

Activities under the Company’s stock option plans for the three months ended March 31, 2018 were as follows:

	Options Outstanding
	Number of Options			Weighted- Average Exercise Price Per Share
Balances at December 31, 2017		6,503,458		$	8.157
Options granted		1,261,400			26.215
Options exercised		(425,139	)		6.122
Option forfeited/expired		(33,764	)		15.491
Balances at March 31, 2018		7,305,955		$	11.360
Options exercisable at March 31, 2018		3,600,751		$	5.957

Total Stock-based Compensation Recognized

Total stock-based compensation recorded related to options granted to employees and non-employees and employee stock purchase plan was as follows (in thousands):

	Three Months Ended
	March 31,
	2018		2017
Stock-based compensation expense:
Research and development	$	1,808	$	1,227
General and administrative		1,880		1,520
Total stock-based compensation expense	$	3,688	$	2,747

Net Loss Per Share (Tables)

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share

	Three Months Ended
	March 31,
	2018		2017
Options to purchase common stock		7,199,679		7,055,207
Total		7,199,679		7,055,207

Basis of Presentation and Summary of Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($)
$ in Thousands

Mar. 31, 2018

Dec. 31, 2017

Mar. 31, 2017

Dec. 31, 2016

Cash And Cash Equivalents [Abstract]

Cash and cash equivalents

$ 142,155

$ 177,548

^[1]

$ 85,662

$ 104,645

Restricted cash

917

^[1]

917

Total

$ 143,072

$ 178,465

$ 86,579

$ 105,562

[1]	The condensed balance sheet as of December 31, 2017 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017.

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)
$ in Thousands

Mar. 31, 2018

Jan. 01, 2018

Dec. 31, 2017

^[1]

Summary Of Significant Accounting Policies [Line Items]

Increase in accumulated deficit balance

$ (245,870)

$ (219,465)

Adjustments | ASC 606

Summary Of Significant Accounting Policies [Line Items]

Increase in accumulated deficit balance

$ (9,761)

$ (10,900)

[1]	The condensed balance sheet as of December 31, 2017 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017.

Basis of Presentation and Summary of Significant Accounting Policies - Summary Impact of Adopting ASC 606 on Select Unaudited Condensed Balance Sheet Line Items (Details) - USD ($)
$ in Thousands

Mar. 31, 2018

Jan. 01, 2018

Dec. 31, 2017

^[1]

Liabilities

$ 1,035

$ 1

46,988

40,559

255,053

264,704

Stockholders' Equity

ASC 606 | Balances Without the Adoption of ASC 606

(245,870)

$ (219,465)

Liabilities

1,154

44,879

247,282

Stockholders' Equity

(236,109)

ASC 606 | Adjustments

Liabilities

(119)

2,109

7,771

Stockholders' Equity

Accrued Liabilities Current [Abstract]

$ (9,761)

$ (10,900)

[1]	The condensed balance sheet as of December 31, 2017 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017.

- Definition

The carrying amount of consideration received or receivable as of the balance sheet date on potential earnings that were not recognized as revenue in conformity with GAAP, and which are expected to be recognized as such within one year or the normal operating cycle, if longer, including sales, license fees, and royalties, but excluding interest income.

+ References + Details

- Definition

The noncurrent portion of deferred revenue amount as of balance sheet date. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized, and is not expected to be recognized in the next twelve months. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

+ References + Details

Basis of Presentation and Summary of Significant Accounting Policies - Summary Impact of Adopting ASC 606 on Select Unaudited Condensed Statement of Operations Line Items (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ 14,184	$ 11,653
Loss from Operations	(15,630)	(8,614)
Loss before provision for income taxes	(14,395)	(8,258)
Provision for income taxes	1,098	(1)
Net loss	$ (15,493)	$ (8,257)
Net loss per share, basic and diluted	$ (0.40)	$ (0.23)
ASC 606 \| Balances Without the Adoption of ASC 606
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ 12,626
Loss from Operations	(17,188)
Loss before provision for income taxes	(15,953)
Provision for income taxes	1,217
Net loss	$ (17,170)
Net loss per share, basic and diluted	$ (0.44)
ASC 606 \| Adjustments
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ 1,558
Loss from Operations	1,558
Loss before provision for income taxes	1,558
Provision for income taxes	(119)
Net loss	$ 1,677
Net loss per share, basic and diluted	$ 0.04

Basis of Presentation and Summary of Significant Accounting Policies - Summary Impact of Adopting ASC 606 on Select Unaudited Condensed Statement of Cash Flows Line Items (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (15,493)	$ (8,257)
Changes in operating assets and liabilities
Accrued liabilities, income tax payable and other long-term liabilities	1,145	(1,809)
Deferred revenue	(14,134)	$ (11,583)
ASC 606 \| Balances Without the Adoption of ASC 606
Cash flows from operating activities:
Net loss	(17,170)
Changes in operating assets and liabilities
Accrued liabilities, income tax payable and other long-term liabilities	1,264
Deferred revenue	(12,576)
ASC 606 \| Adjustments
Cash flows from operating activities:
Net loss	1,677
Changes in operating assets and liabilities
Accrued liabilities, income tax payable and other long-term liabilities	(119)
Deferred revenue	$ (1,558)

Fair Value Measurements and Investments - Schedule of Short-Term Investments Subject to Fair Value Measurements on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 351,323	$ 361,986
Gross Unrealized Holding Losses	(203)	(67)
Aggregate Fair Value	351,120	361,919
Level I \| Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	130,882	164,440
Aggregate Fair Value	130,882	164,440
Level I \| Restricted cash (money market funds)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	917	917
Aggregate Fair Value	917	917
Level I \| U. S. Government bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	219,524	196,629
Gross Unrealized Holding Losses	(203)	(67)
Aggregate Fair Value	$ 219,321	$ 196,562

Fair Value Measurements and Investments - Additional Information (Details)	Mar. 31, 2018 USD ($)
Fair Value Disclosures [Abstract]
Contractual maturities of longer than one year	$ 0

Accrued Liabilities - Summary of Accrued Liabilities (Details) - USD ($)
$ in Thousands

Mar. 31, 2018

Dec. 31, 2017

Research and clinical expenses

$ 12,381

$ 10,068

Payroll and related expenses

2,140

4,526

Legal and professional expenses

1,558

1,523

Other accrued expenses

256

265

Total

$ 16,335

$ 16,382

^[1]

[1]	The condensed balance sheet as of December 31, 2017 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017.

Research and Collaboration Agreements - AbbVie Ireland Unlimited Company - Additional Information (Details)	1 Months Ended		3 Months Ended
	Jul. 31, 2017 USD ($)	Apr. 30, 2016 USD ($) Agreement Target AccountingUnit	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($) Target	Dec. 31, 2017 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue			$ 302,041,000		$ 305,263,000
AbbVie Ireland Unlimited Company
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment received		$ 14,000,000
Sublicense fees paid		1,000,000
Total transaction price		30,000,000
Estimated sublicense fees		$ 4,200,000
Number of accounting units \| AccountingUnit		2,000,000
Revenue recognized from collaborative arrangement			2,700,000	$ 1,400,000
AbbVie Ireland Unlimited Company \| Collaborative Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of collaboration agreements \| Agreement		2
Percentage of net profits or net losses related to development costs		35.00%
Number of targets selected \| Target				1
Amount due from agreement			$ 0
AbbVie Ireland Unlimited Company \| Collaborative Arrangement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targets \| Target		2
AbbVie Ireland Unlimited Company \| CD71 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment received	$ 14,000,000
Sublicense fees paid	$ 1,000,000	$ 1,000,000
Total transaction price		29,800,000
Milestone payment received		14,000,000
Revenue recognition upon performance obligation, service period			5 years
Deferred revenue			$ 17,000,000		11,200,000
AbbVie Ireland Unlimited Company \| CD71 Agreement \| Up Front Payment Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received		20,000,000
AbbVie Ireland Unlimited Company \| CD71 Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments receivable upon achieving development, regulatory and commercial milestones		470,000,000
AbbVie Ireland Unlimited Company \| Discovery Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognition upon performance obligation		10,000,000
Estimated research service period			5 years
Deferred revenue			$ 6,200,000		$ 6,800,000
AbbVie Ireland Unlimited Company \| Discovery Agreement \| Up Front Payment Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received		10,000,000
AbbVie Ireland Unlimited Company \| Discovery Agreement \| Maximum \| Development, Regulatory and Commercial Milestone Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent milestone payments receivable		$ 275,000,000

Research and Collaboration Agreements - Amgen, Inc - Additional Information (Details)

1 Months Ended

3 Months Ended

Sep. 29, 2017

USD ($)

Target

Oct. 31, 2017

USD ($)

$ / shares

Mar. 31, 2018

USD ($)

$ / shares

Dec. 31, 2017

USD ($)

$ / shares

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Common stock, par value | $ / shares

$ 0.00001

Accrued liabilities

$ 16,335,000

$ 16,382,000

^[1]

Amgen Inc | EGFR Products

302,041,000

305,263,000

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Amgen Inc | Amgen Other Products

43,700,000

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration and License Agreement

4,400,000

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Revenue recognized from collaborative arrangement

1,300,000

Amount due from agreement

Collaboration and License Agreement | EGFR Products

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration and License Agreement | Amgen Other Products

43,700,000

45,300,000

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]