Description of Business and Summary of Significant Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Leases	Leases In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, Leases (“ASC 842”), to enhance the transparency and comparability of financial reporting related to leasing arrangements. In November 2019, the FASB issued ASU 2019-10, Financial Instruments — Credit losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842), which provided a one-year deferral of the effective dates of ASC 842. The Company adopted ASC 842 on January 1, 2020, or the effective date, and used the effective date as its date of initial application. At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and lease liabilities. The Company has elected not to recognize on the balance sheet leases with terms of one year or less. Lease liabilities and corresponding right-of-use assets are recorded based on the present value of lease payments over the expected remaining lease term. However, certain adjustments to the right-of-use asset may be required for items such as prepaid and deferred rent. In calculating the present value of the lease payments, the Company has elected to apply the discount rate based on the remaining lease term as of the transition date, January 1, 2020. However, as the rate implicit in the lease is not readily determinable, the Company utilizes its incremental borrowing rates, which are the rates incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. The Company has elected to account for the lease and non-lease components of each of its operating leases as a single lease component. The operating right-of-use asset recorded on the balance sheet is amortized on a straight-line basis as lease expense.
Revenue Recognition for Contracts with Customers	Revenue Recognition for Contracts with Customers The Company’s revenues are generated primarily through collaborative research, license, development and commercialization agreements. Effective January 1, 2019, the Company adopted ASU No. 2014-09, Revenue: Revenue from Contracts with Customers (“ASC 606”), using the modified retrospective transition method. Under this method, results for reporting periods beginning on January 1, 2019 are presented under ASC 606, while prior period amounts are not adjusted and continue to be reported in accordance with ASC Topic 605, Revenue Recognition (“ASC 605”). The Company applied the modified retrospective transition method to contracts that were not completed as of January 1, 2019. ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company evaluates the performance obligations promised in the contract that are based on goods and services that will be transferred to the customer and determines whether those obligations are both (i) capable of being distinct and (ii) distinct in the context of the contract. Goods or services that meet these criteria are considered distinct performance obligations. If both these criteria are not met, the goods and services are combined into a single performance obligation. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, these options are considered performance obligations. The exercise of a material right is accounted for as a contract modification for accounting purposes. The Company recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied at a point in time or over time, and if over time this is based on the use of an output or input method. For the three months ended March 31, 2020, the Company reduced revenue recognition by $1.6 million for changes in total estimated time to be incurred in the future to satisfy the performance obligation. Amounts received prior to revenue recognition are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue within current liabilities in the accompanying condensed consolidated balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue – noncurrent. Amounts recognized as revenue, but not yet received or invoiced are generally recognized as contract assets in the Other current assets line item in the condensed consolidated balance sheets. Milestone Payments – If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price 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 Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. Royalties – For arrangements that include sales-based royalties, including milestone payments based on a level of sales, which are the result of a customer-vendor relationship and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied or partially satisfied. To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements. Significant Financing Component – In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company assessed each of its revenue arrangements in order to determine whether a significant financing component exists and concluded that a significant financing component does not exist in any of its arrangements. Collaborative Arrangements – The Company has entered into collaboration agreements, which are within the scope of ASC 606, to discover, develop, manufacture and commercialize product candidates. The terms of these agreements typically contain multiple promises or obligations, which may include: (1) licenses, or options to obtain licenses, to use the Company’s technology, (2) research and development activities to be performed on behalf of the collaboration partner, and (3) in certain cases, services in connection with the manufacturing of preclinical and clinical material. Payments the Company receives under these arrangements typically include one or more of the following: non-refundable, upfront license fees; option exercise fees; funding of research and/or development efforts; clinical and development, regulatory, and sales milestone payments; and royalties on future product sales. The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements (“ASC 808”) to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and, therefore, are within the scope of ASC 606. For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to ASC 606. For those elements of the arrangement that are accounted for pursuant to ASC 606, the Company applies the five-step model described above. For a complete discussion of accounting for collaboration revenues, see Note 8, “Collaboration and license agreements.”
Accounting Standards Updates	Accounting Standards Updates In February 2016, the FASB issued ASU 2016-02, Leases (“ASC 842”). In November 2019, the FASB issued ASU 2019-10, Financial Instruments — Credit losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842), which provided a one-year deferral of the effective dates of ASC 842. This standard was issued in order to improve comparability among organizations by recognizing lease assets and liabilities for all leases, with certain exceptions, on the balance sheet. The Company elected to early adopt ASC 842 on January 1, 2020, or the effective date, and used the effective date as its date of initial application. As such, the Company did not adjust prior period amounts. The Company also elected to adopt the package of practical expedients upon transition, which permits companies to not reassess lease identification, classification, and initial direct costs under ASC 842 for leases that commenced prior to the effective date. Upon adoption, the Company recorded lease liabilities of $11.6 million, right-of-use assets of $6.8 million, and a reduction of existing deferred rent balances of $4.8 million on the balance sheet as of January 1, 2020. In May 2014, the Financial Accounting Standards Board, or FASB, issued ASC 606, which superseded the revenue requirements in ASC 605. In 2015 and 2016, the FASB issued additional ASUs related to ASC 606 that delayed the effective date of the guidance and clarified various aspects of the new revenue guidance, including principal versus agent considerations, identifying performance obligations, and licensing, and they include other improvements and practical expedients. Effective January 1, 2019, the Company adopted ASC 606 using the modified retrospective transition method. As a result of adopting ASC 606, the Company recorded a $1.0 million transition adjustment in the first quarter of 2019 to reduce the opening balance of accumulated deficit as of January 1, 2019 primarily as a result of the treatment of the up-front consideration received from the Company’s collaboration agreements under prior revenue recognition guidance. During the three months ended March 31, 2020, the Company recognized $3.7 million in revenue that was included in the deferred revenue balance as of December 31, 2019. The most significant change to the Company’s revenue recognition as a result of the adoption of ASC 606 relates to the accounting for certain option fees and milestone payments in determining the transaction price (step (iii)), and the revenue recognition pattern (step (v)) related to the Company’s development and commercial license agreement with Servier. Under ASC 605, the option fees payable by the Company to exercise the 50/50 co-development and co-promotion option was accounted for as a reduction in the arrangement consideration, and certain development milestones that may be earned for early-stage pre-IND development milestones were included in the arrangement consideration as the early-stage pre-IND development milestones were deemed to be non-substantive. Under ASC 606, the option fees were not accounted for as a reduction in the transaction price as the option fees are contingent upon Servier’s exercise of its commercial (customer) options on licensed product candidates, and the milestone payments were excluded from the transaction price based on the assessment of the most likely amount and application of the variable consideration constraint, since the milestones relate to successful achievement of certain developmental goals, which may not be achieved. In addition, under ASC 605, the Company recognized revenue on a straight‑line basis over the period the Company expected to complete its obligations. Under ASC 606, the Company recognizes revenue based on the proportional performance of the services related to the performance obligation expected. In August 2018, the FASB issued ASU 2018-13, Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). ASU 2018-13 is intended to improve the effectiveness of disclosures in the notes to financial statements related to fair value measurements in Topic 820. This ASU will become effective for annual periods beginning after December 15, 2019, including interim periods within that period, and early adoption is permitted. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements and related disclosures. In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808)—Clarifying the Interaction between Topic 808 and ASC 606 (“ASU 2018-18”). The amendments in ASU 2018-18 make targeted improvements to GAAP for collaborative arrangements by clarifying that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all the guidance in ASC 606 should be applied, including recognition, measurement, presentation, and disclosure requirements. In addition, unit-of-account guidance in ASU 2018-18 was aligned with the guidance in ASC 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of ASC 606. ASU 2018-18 is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted, including adoption in any interim period. The amendments should be applied retrospectively to the date of initial application of ASC 606. The Company adopted this guidance effective January 1, 2019 with its initial application of ASC 606. The adoption of the standard did not have an impact on the Company’s condensed consolidated financial statements.

Description of Business and Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, Leases (“ASC 842”), to enhance the transparency and comparability of financial reporting related to leasing arrangements. In November 2019, the FASB issued ASU 2019-10, Financial Instruments — Credit losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842), which provided a one-year deferral of the effective dates of ASC 842. The Company adopted ASC 842 on January 1, 2020, or the effective date, and used the effective date as its date of initial application.

At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and lease liabilities. The Company has elected not to recognize on the balance sheet leases with terms of one year or less. Lease liabilities and corresponding right-of-use assets are recorded based on the present value of lease payments over the expected remaining lease term. However, certain adjustments to the right-of-use asset may be required for items such as prepaid and deferred rent. In calculating the present value of the lease payments, the Company has elected to apply the discount rate based on the remaining lease term as of the transition date, January 1, 2020. However, as the rate implicit in the lease is not readily determinable, the Company utilizes its incremental borrowing rates, which are the rates incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment.

The Company has elected to account for the lease and non-lease components of each of its operating leases as a single lease component. The operating right-of-use asset recorded on the balance sheet is amortized on a straight-line basis as lease expense.

Revenue Recognition for Contracts with Customers

The Company’s revenues are generated primarily through collaborative research, license, development and commercialization agreements.

Effective January 1, 2019, the Company adopted ASU No. 2014-09, Revenue: Revenue from Contracts with Customers (“ASC 606”), using the modified retrospective transition method. Under this method, results for reporting periods beginning on January 1, 2019 are presented under ASC 606, while prior period amounts are not adjusted and continue to be reported in accordance with ASC Topic 605, Revenue Recognition (“ASC 605”). The Company applied the modified retrospective transition method to contracts that were not completed as of January 1, 2019. ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation.

At contract inception, once the contract is determined to be within the scope of ASC 606, the Company evaluates the performance obligations promised in the contract that are based on goods and services that will be transferred to the customer and determines whether those obligations are both (i) capable of being distinct and (ii) distinct in the context of the contract. Goods or services that meet these criteria are considered distinct performance obligations. If both these criteria are not met, the goods and services are combined into a single performance obligation. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, these options are considered performance obligations. The exercise of a material right is accounted for as a contract modification for accounting purposes.

The Company recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied at a point in time or over time, and if over time this is based on the use of an output or input method. For the three months ended March 31, 2020, the Company reduced revenue recognition by $1.6 million for changes in total estimated time to be incurred in the future to satisfy the performance obligation.

Amounts received prior to revenue recognition are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue within current liabilities in the accompanying condensed consolidated balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue – noncurrent. Amounts recognized as revenue, but not yet received or invoiced are generally recognized as contract assets in the Other current assets line item in the condensed consolidated balance sheets.

Milestone Payments – If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price 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 Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received.

Royalties – For arrangements that include sales-based royalties, including milestone payments based on a level of sales, which are the result of a customer-vendor relationship and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied or partially satisfied. To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements.

Significant Financing Component – In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company assessed each of its revenue arrangements in order to determine whether a significant financing component exists and concluded that a significant financing component does not exist in any of its arrangements.

Collaborative Arrangements – The Company has entered into collaboration agreements, which are within the scope of ASC 606, to discover, develop, manufacture and commercialize product candidates. The terms of these agreements typically contain multiple promises or obligations, which may include: (1) licenses, or options to obtain licenses, to use the Company’s technology, (2) research and development activities to be performed on behalf of the collaboration partner, and (3) in certain cases, services in connection with the manufacturing of preclinical and clinical material. Payments the Company receives under these arrangements typically include one or more of the following: non-refundable, upfront license fees; option exercise fees; funding of research and/or development efforts; clinical and development, regulatory, and sales milestone payments; and royalties on future product sales.

The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements (“ASC 808”) to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and, therefore, are within the scope of ASC 606. For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to ASC 606. For those elements of the arrangement that are accounted for pursuant to ASC 606, the Company applies the five-step model described above.

For a complete discussion of accounting for collaboration revenues, see Note 8, “Collaboration and license agreements.”

Accounting Standards Updates

In February 2016, the FASB issued ASU 2016-02, Leases (“ASC 842”). In November 2019, the FASB issued ASU 2019-10, Financial Instruments — Credit losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842), which provided a one-year deferral of the effective dates of ASC 842. This standard was issued in order to improve comparability among organizations by recognizing lease assets and liabilities for all leases, with certain exceptions, on the balance sheet. The Company elected to early adopt ASC 842 on January 1, 2020, or the effective date, and used the effective date as its date of initial application. As such, the Company did not adjust prior period amounts. The Company also elected to adopt the package of practical expedients upon transition, which permits companies to not reassess lease identification, classification, and initial direct costs under ASC 842 for leases that commenced prior to the effective date. Upon adoption, the Company recorded lease liabilities of $11.6 million, right-of-use assets of $6.8 million, and a reduction of existing deferred rent balances of $4.8 million on the balance sheet as of January 1, 2020.

In May 2014, the Financial Accounting Standards Board, or FASB, issued ASC 606, which superseded the revenue requirements in ASC 605. In 2015 and 2016, the FASB issued additional ASUs related to ASC 606 that delayed the effective date of the guidance and clarified various aspects of the new revenue guidance, including principal versus agent considerations, identifying performance obligations, and licensing, and they include other improvements and practical expedients. Effective January 1, 2019, the Company adopted ASC 606 using the modified retrospective transition method.

As a result of adopting ASC 606, the Company recorded a $1.0 million transition adjustment in the first quarter of 2019 to reduce the opening balance of accumulated deficit as of January 1, 2019 primarily as a result of the treatment of the up-front consideration received from the Company’s collaboration agreements under prior revenue recognition guidance. During the three months ended March 31, 2020, the Company recognized $3.7 million in revenue that was included in the deferred revenue balance as of December 31, 2019.

The most significant change to the Company’s revenue recognition as a result of the adoption of ASC 606 relates to the accounting for certain option fees and milestone payments in determining the transaction price (step (iii)), and the revenue recognition pattern (step (v)) related to the Company’s development and commercial license agreement with Servier. Under ASC 605, the option fees payable by the Company to exercise the 50/50 co-development and co-promotion option was accounted for as a reduction in the arrangement consideration, and certain development milestones that may be earned for early-stage pre-IND development milestones were included in the arrangement consideration as the early-stage pre-IND development milestones were deemed to be non-substantive. Under ASC 606, the option fees were not accounted for as a reduction in the transaction price as the option fees are contingent upon Servier’s exercise of its commercial (customer) options on licensed product candidates, and the milestone payments were excluded from the transaction price based on the assessment of the most likely amount and application of the variable consideration constraint, since the milestones relate to successful achievement of certain developmental goals, which may not be achieved. In addition, under ASC 605, the Company recognized revenue on a straight‑line basis over the period the Company expected to complete its obligations. Under ASC 606, the Company recognizes revenue based on the proportional performance of the services related to the performance obligation expected.

In August 2018, the FASB issued ASU 2018-13, Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). ASU 2018-13 is intended to improve the effectiveness of disclosures in the notes to financial statements related to fair value measurements in Topic 820. This ASU will become effective for annual periods beginning after December 15, 2019, including interim periods within that period, and early adoption is permitted. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements and related disclosures.

In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808)—Clarifying the Interaction between Topic 808 and ASC 606 (“ASU 2018-18”). The amendments in ASU 2018-18 make targeted improvements to GAAP for collaborative arrangements by clarifying that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all the guidance in ASC 606 should be applied, including recognition, measurement, presentation, and disclosure requirements. In addition, unit-of-account guidance in ASU 2018-18 was aligned with the guidance in ASC 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of ASC 606. ASU 2018-18 is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted, including adoption in any interim period. The amendments should be applied retrospectively to the date of initial application of ASC 606. The Company adopted this guidance effective January 1, 2019 with its initial application of ASC 606. The adoption of the standard did not have an impact on the Company’s condensed consolidated financial statements.