Collaboration Agreements - Additional Information (Details)		3 Months Ended								12 Months Ended
	Feb. 10, 2017 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) Milestone	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jul. 17, 2020 USD ($)
Collaboration Agreements:
Collaboration revenue		$ 1,037,000	$ 34,611,000	$ 39,376,000	$ 4,081,000	$ 4,767,000	$ 4,231,000	$ 3,080,000	$ 3,885,000	$ 79,105,000	$ 15,963,000	$ 14,804,000
Contract with customer, liability, current						6,411,000					6,411,000
Contract with customer, liability, noncurrent		8,987,000				30,637,000				8,987,000	30,637,000
Contract liability/deferred revenue		8,987,000				37,048,000				8,987,000	37,048,000	40,660,000
Accounts receivable from collaboration		1,230,000				3,374,000				1,230,000	3,374,000
Research and development expense										106,823,000	85,757,000	72,741,000
Allergan
Collaboration Agreements:
Agreed to share maximum amount development cost	$ 75,000,000.0
Premium percentage on agreed contribution development cost amount	25.00%
Allergan Agreement
Collaboration Agreements:
Deferred revenue, cumulative catch up revenue recognized										36,000,000.0
Collaborative Arrangement
Collaboration Agreements:
Collaboration revenue	$ 50,000,000.0									12,500,000
Cost of reimbursable expenses										48,100,000	16,000,000.0	$ 14,800,000
Contract with customer, liability, current						6,400,000					6,400,000
Contract with customer, liability, noncurrent						30,600,000					30,600,000
Contract liability/deferred revenue		0								0
Accounts receivable from collaboration		1,000,000.0				$ 3,400,000				1,000,000.0	$ 3,400,000
Collaborative Arrangement | Milestone Scenario One
Collaboration Agreements:
Potential milestone payments										$ 631,000,000.0
Number of milestones | Milestone										7
Collaborative Arrangement | Milestone Scenario Two
Collaboration Agreements:
Potential milestone payments										$ 2,140,000,000
Number of milestones | Milestone										12
BeiGene Agreement
Collaboration Agreements:
Collaboration revenue										$ 31,000,000.0
Contract with customer, liability, noncurrent		$ 9,000,000.0								9,000,000.0
Agreed to pay maximum amount development and regulatory costs										45,000,000.0
Upfront cash payment received										40,000,000.0
Research and development expense										0
Incremental costs										3,500,000
BeiGene Agreement | Other Assets
Collaboration Agreements:
Incremental costs										800,000
BeiGene Agreement | General and Administrative
Collaboration Agreements:
Incremental costs										2,700,000
BeiGene Agreement | Maximum
Collaboration Agreements:
Potential milestone payments										500,000,000.0
BeiGene Agreement | Development and Regulatory | Maximum
Collaboration Agreements:
Potential milestone payments										113,800,000
BeiGene Agreement | Sales Milestone Payments | Maximum
Collaboration Agreements:
Potential milestone payments										385,000,000.0
Bei Gene Limited
Collaboration Agreements:
Contract liability/deferred revenue													$ 40,000,000.0
Arbutus Agreement
Collaboration Agreements:
Research and development expense										$ 200,000