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Collaboration and License Agreements and Supply Agreements - Additional Information (Details) | 1 Months Ended | 3 Months Ended | 6 Months Ended |  |
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Apr. 30, 2020 USD ($) | Mar. 31, 2020 USD ($) | Feb. 29, 2020 USD ($) | May 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Aug. 31, 2018 USD ($) Program | Jul. 31, 2018 Program | Sep. 30, 2017 USD ($) | Aug. 31, 2017 USD ($) Program | Jun. 30, 2016 USD ($) | Mar. 31, 2015 USD ($) | Sep. 30, 2014 USD ($) | May 31, 2014 USD ($) | Jun. 30, 2020 USD ($) | Mar. 31, 2020 USD ($) | Jun. 30, 2019 USD ($) | Jun. 30, 2020 USD ($) | Jun. 30, 2019 USD ($) | Dec. 31, 2019 USD ($) | Jan. 01, 2019 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent payments of embedded derivative and related liability |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000 |  |  | $ 100,000 |  | $ 100,000 |
EMD Serono |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Recognition of up front payment |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,000,000.0 |  |  | 20,000,000.0 |  |  |
Changes in deferred revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 600,000 |  |  |
The Leukemia & Lymphoma Society, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research development and commercialization agreement termination period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 years |  |  |
Research development and commercialization agreement termination description |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | The LLS Agreement terminates upon the earlier of (a) fulfillment of all payment obligations by both parties or (b) 12 years after the effective date. LLS may terminate the LLS Agreement at any time with 60 days’ prior written notice. Either the Company or LLS has the right to terminate the LLS Agreement based on the other party’s uncured material breach. |  |  |
First Cytokine-Derivative Program | Merck Sharp & Dohme Corp |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extended research term |  | 1 year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront payment received |  | $ 5,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue, remaining performance obligation, amount |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 |  |  |  |  |
Recognition of up front payment |  | 50,500,000 |  |  |  |  |  |  |  |  |  |  |  |  | 50,500,000 |  |  |  |  |
Transaction price |  | 65,000,000.0 | $ 60,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Constrained variable consideration |  |  | $ 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue reallocated property rights |  | 7,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Incremental revenue recognized reallocated target programs |  | $ 500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated service period |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Incremental revenue recognized |  | $ 1,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Adjustments to transaction price |  | 5,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative catch-up in revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000.0 |  |  |  |  |
Development and Manufacturing Services | Bristol-Myers Squibb Company ("BMS") |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront payment received | $ 2,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Celgene Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront, nonrefundable payment received |  |  |  |  |  |  |  |  |  |  |  | $ 83,100,000 |  |  |  |  |  |  |  |
Contingent payment received |  |  |  |  |  |  |  |  |  |  | $ 15,000,000.0 |  |  |  |  |  |  |  |  |
Milestone payment received |  |  |  |  |  |  |  |  |  | $ 25,000,000.0 |  |  |  |  |  |  |  |  |  |
Additional milestone payment received |  |  |  |  |  |  |  |  |  | $ 10,000,000.0 |  |  |  |  |  |  |  |  |  |
Option fee payment received |  |  |  |  |  |  |  |  | $ 12,500,000 |  |  |  |  |  |  |  |  |  |  |
Milestone revenue recognized |  |  |  |  | $ 10,000,000.0 |  |  | $ 10,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |
Contingent payments |  |  |  | $ 275,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Option maintenance fee |  |  |  |  |  |  |  |  | $ 12,500,000 |  |  |  |  |  |  |  |  |  |  |
Number of programs advancing through preclinical development | Program |  |  |  |  |  |  |  |  | 4 |  |  |  |  |  |  |  |  |  |  |
Deferred revenue |  |  |  |  |  |  |  |  | $ 8,200,000 |  |  |  |  | 3,300,000 |  |  | $ 3,300,000 |  | 3,000,000.0 |
Revenue, remaining performance obligation, amount |  |  |  |  |  |  |  |  | 20,700,000 |  |  |  |  |  |  |  |  |  |  |
Celgene Agreement | ASC 606 | Difference between Revenue Guidance in Effect before and after Topic 606 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (4,500,000)
Celgene Agreement | First Performance Obligation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue, remaining performance obligation, amount |  |  |  |  |  |  |  |  | 8,200,000 |  |  |  |  |  |  |  |  |  |  |
Celgene Agreement | Future Services on Collaboration Joint Steering Committee ("JSC") |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue, remaining performance obligation, amount |  |  |  |  |  |  |  |  | 200,000 |  |  |  |  |  |  |  |  |  |  |
Celgene Agreement | Third Performance Obligation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue, remaining performance obligation, amount |  |  |  |  |  |  |  |  | $ 12,300,000 |  |  |  |  |  |  |  |  |  |  |
Partially Unsatisfied Performance Obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,000,000.0 |  | $ 1,000,000.0 | 2,000,000.0 | $ 1,900,000 |  |
Partially Unsatisfied Performance Obligations | EMD Serono |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,000,000.0 |  | 2,300,000 |  |
Research and Development Services |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  |  |  |  |  |  |  |  |  |  |  | 300,000 |  | 100,000 | 400,000 | 300,000 |  |
Research and Development Services | EMD Serono |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  |  |  |  |  |  |  |  |  |  |  | 500,000 |  | 900,000 | 800,000 | 1,700,000 |  |
2018 Celgene Master Services Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other revenue-related parties |  |  |  |  |  |  |  |  |  |  |  |  |  | 300,000 |  | 500,000 | 1,200,000 | 1,000,000.0 |  |
2018 Merck Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront payment received |  |  |  |  |  | $ 60,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred revenue |  |  |  |  |  |  |  |  |  |  |  |  |  | 30,800,000 |  |  | 30,800,000 |  | 31,900,000 |
Number of research programs | Program |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue recognized performance obligation |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 47,100,000 |  |  |  |  |
Transaction price |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 60,000,000.0 |  |  |  |  |
2018 Merck Agreement | Celgene Corporation | ASC 606 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in deferred revenue due to adoption of new accounting policy |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 6,300,000
2018 Merck Agreement | Merck Sharp & Dohme Corp |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront payment received |  |  |  |  |  | $ 60,000,000.0 |  |  |  |  |  |  |  |  |  |  | 60,000,000.0 |  |  |
Number of research programs | Program |  |  |  |  |  |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue from first performance obligation |  |  |  |  |  | 7,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Recognition of up front payment |  |  |  |  |  | 47,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue recognized performance obligation |  |  |  |  |  | 700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extension option fee associated with contingent program |  |  |  |  |  | 4,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in revenue |  | (5,100,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Embedded interest associated with upfront payment |  |  |  |  |  |  |  |  |  |  |  |  |  | 500,000 |  | 800,000 | 1,100,000 | 1,700,000 |  |
FTE Funding Received |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,200,000 |  | 900,000 | 2,500,000 | 1,700,000 |  |
Revenue recognition aggregate milestone payments eligible to receive |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,600,000,000 |  |  |
Milestone method revenue recognition description |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | If one or more products from each of the target programs are developed for non-oncology or a single indication, the Company will be eligible for reduced aggregate milestone payments. In addition, the Company is eligible to receive tiered royalties ranging from mid-single digit to low teen percentages on the worldwide sales of any commercial products that may result from the collaboration. |  |  |
2018 Merck Agreement | Merck Sharp & Dohme Corp | First Target Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in revenue |  | (6,200,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2018 Merck Agreement | Merck Sharp & Dohme Corp | Second Target Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in revenue |  | $ 1,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2018 Merck Agreement | Merck Sharp & Dohme Corp | Partially Unsatisfied Performance Obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,200,000 |  | 3,700,000 | $ 6,100,000 | 6,700,000 |  |
2018 Merck Agreement | Merck Sharp & Dohme Corp | ASC 606 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total interest of unearned revenue |  |  |  |  |  |  |  |  |  |  |  |  |  | 7,400,000 |  |  | 7,400,000 |  |  |
Collaboration Agreement | EMD Serono |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Up-front, nonrefundable and non-creditable payment received |  |  |  |  |  |  |  |  |  |  |  |  | $ 10,000,000.0 |  |  |  |  |  |  |
MDA Agreement | EMD Serono |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred revenue |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 |  |  | 0 |  | $ 800,000 |
Up-front, nonrefundable and non-creditable payment received |  |  |  |  |  |  |  |  |  |  |  | $ 10,000,000.0 |  |  |  |  |  |  |  |
Maximum amount eligible to receive for each product developed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 52,500,000 |  |  |
Milestone Payment and Supply Agreement | EMD Serono |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  |  |  |  |  |  |  |  |  |  |  | 300,000 |  | 1,500,000 | 2,300,000 | 1,500,000 |  |
Supply Agreement | Vaxcyte, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000 |  | $ 0 | $ 100,000 | $ 300,000 |  |
Research Development and Commercialization Agreement | The Leukemia & Lymphoma Society, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Milestone payment received |  |  |  |  |  | 1,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum contribution in clinical development |  |  |  |  |  | 6,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Initial milestone payment |  |  |  |  |  | 500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum aggregate payment |  |  |  |  |  | $ 19,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |

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