Collaboration and License Agreements and Supply Agreements - Additional Information (Details)	1 Months Ended															3 Months Ended		12 Months Ended
	Oct. 31, 2020 USD ($)	Aug. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)	Feb. 29, 2020 USD ($)	Sep. 30, 2019 USD ($)	May 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Aug. 31, 2018 USD ($)	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 ($)	May 31, 2014 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments of embedded derivative and related liability																$ 100,000		$ 200,000
2019 EMD Serono Supply Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue																1,000,000.0		1,000,000.0
Total revenue																$ 100,000	$ 2,000,000.0
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.
BMS Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of programs advancing through preclinical development | Program											4
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
Deferred revenue											8,200,000					$ 0		0
Revenue, remaining performance obligation, amount											20,700,000
BMS Agreement | First Performance Obligation
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue, remaining performance obligation, amount											8,200,000
BMS Agreement | Future Services on Collaboration Joint Steering Committee ("JSC")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue, remaining performance obligation, amount											200,000
BMS 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																0	1,000,000.0
Research and Development Services
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenue																300,000	100,000
Research and Development Services | EMD Serono
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenue																200,000	300,000
Research and Development Services | Vaxcyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Pass-through costs from CMOs																		200,000
2018 BMS Master Services Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue																2,500,000		1,200,000
Other revenue-related parties																900,000	900,000
2018 Merck Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue																9,400,000		18,500,000
2018 Merck Agreement | Merck Sharp & Dohme Corp
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of research programs | Program									3
Upfront payment received								$ 60,000,000.0								60,000,000.0
Revenue from first performance obligation								7,300,000
Recognition of up front payment								47,100,000
Revenue performance obligation amounts recognized in revenues								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																200,000	600,000
FTE Funding Received																1,200,000	1,300,000
Revenue recognition aggregate contingent payments eligible to receive																$ 500,000,000
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																$ 9,100,000	900,000
2018 Merck Agreement | Merck Sharp & Dohme Corp | Accounting Standards Update 2014-09
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total interest of unearned revenue																7,300,000
First Cytokine-Derivative Program | Merck Sharp & Dohme Corp
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received			5,000,000.0
Recognition of up front payment			$ 50,500,000														50,500,000
Extended research term			1 year
Transaction price			$ 65,000,000.0	$ 60,000,000.0
Constrained variable consideration				$ 5,000,000.0
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
2020 Merck Master Services Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenue																1,400,000
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]
Contingent payment received					$ 1,500,000
Milestone payment received	$ 1,000,000.0
Milestone revenue recognized		$ 1,000,000.0
Deferred revenue																0		$ 0
Up-front, nonrefundable and non-creditable payment received														$ 10,000,000.0
Maximum amount eligible to receive for each product developed																52,500,000
Supply Agreement | Vaxcyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenue																$ 1,300,000	$ 36,000
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