Research and Development Collaborations - Narrative (Details)		1 Months Ended		3 Months Ended		12 Months Ended
	Jan. 06, 2020 USD ($)	Sep. 30, 2016 USD ($) program shares	Jun. 30, 2003 USD ($)	Mar. 31, 2020 USD ($) product term program	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2015 USD ($) shares	Feb. 29, 2020 patient	Dec. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues, net				$ 2,709,000	$ 1,767,000
Cost of royalties				125,000	108,000
Accounts receivable				2,507,000					$ 3,244,000
Value of common stock issued				$ 366,000					$ 332,000
Number of program licensed | program		4		4
Collaboration agreement, number of optional additional terms | term				3
Collaboration agreement, optional additional term				1 year
Option fees				$ 7,500,000
Number of payments | payment											2
Exclusivity payment				2,000,000		$ 10,000,000
Research and Development, Net
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenues				0	0
Royalties
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues, net				2,515,000	2,137,000
Genentech, Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development collaboration expense					0
Genentech, Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Amount received for specified clinical development and regulatory objectives				59,000,000
Percentage of royalty rate decrease			2.00%
Cost of royalties				100,000	100,000
Accounts receivable				$ 2,500,000						$ 3,200,000
Royalty rate, percentage of sales (percent)				5.00%
Genentech, Inc. | Royalties
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues, net				$ 2,500,000	2,100,000
Genentech, Inc. | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Eligible to receive contingent cash payment for specified clinical development and regulatory objectives (up to)			$ 115,000,000
Percentage of royalty on net sales			7.50%
Genentech, Inc. | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of royalty on net sales			5.00%
Aurigene
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development collaboration expense				$ 0	$ 0
Issued shares of common stock (in shares) | shares							3,424,026.2
Value of common stock issued							$ 24,300,000
Shares issued of common stock in exchange for waived payment (in shares) | shares		2,041,666
Waived payment of milestone and other payments (up to)		$ 24,500,000
Number of patients in trial | patient								240
Collaboration agreement, number of products required to commercialize (at least) | product				1
Collaboration agreement period				2 years
Milestone payments waived to date				$ 19,500,000
Aurigene | Programs three and four
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Agreement to provide additional funding, if options are exercised (up to)		$ 2,000,000
Payments made under collaboration arrangements				14,500,000
Aurigene | IRAK4, PD1/VISTA,PD1/TIM3 Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Waived payment of milestone and other payments (up to)				$ 42,500,000
ImmuNext
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment due	$ 1,300,000
Option exercise fee	$ 20,000,000
Expiration period (years)	10 years
Semi-annual maintenance fee payments	$ 400,000
Maximum reimbursable expenses	300,000
ImmuNext | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Development milestone payments	4,600,000
Regulatory approval milestone payments	84,300,000
Sales milestone payments	$ 125,000,000.0
Asia | Aurigene | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalty rate, percentage of sales (percent)								10.00%