Commitments and Contingencies - Schedule of Additional Information Related to Operating Leases (Details)	3 Months Ended
	Mar. 31, 2021 ft²
Lessee Lease Description [Line Items]
Expiration Dates, Beginning	2024-04
Expiration Dates, Ending	2030-04
Seattle, WA
Lessee Lease Description [Line Items]
Approximate Square Footage	48,086
Commencement Dates, Beginning	2019-03
Commencement Dates, Ending	2020-09
Expiration Dates, Beginning	2026-12
Expiration Dates, Ending	2028-04
Cambridge, MA
Lessee Lease Description [Line Items]
Approximate Square Footage	56,859
Commencement Dates, Beginning	2019-03
Commencement Dates, Ending	2020-05
Expiration Dates, Beginning	2025-11
Expiration Dates, Ending	2028-02
South San Francisco, CA
Lessee Lease Description [Line Items]
Approximate Square Footage	66,075
Commencement Dates, Beginning	2019-12
Commencement Dates, Ending	2020-10
Expiration Dates, Beginning	2024-04
Expiration Dates, Ending	2030-04