Collaborative and Licensing Agreements - Revenue Recognition (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded	$ 13,089,000	$ 19,485,000	$ 45,474,000	$ 131,424,000
Deferred revenue	44,700,000	48,800,000	44,700,000	48,800,000
Current portion of deferred revenue	44,685,000	45,500,000	44,685,000	45,500,000	$ 45,205,000
Non Current portion of deferred revenue		3,300,000		3,300,000	$ 1,926,000
Research collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded	1,500,000	14,400,000	2,400,000	14,700,000
Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded	300,000	4,000,000.0	12,800,000	4,000,000.0
Licensing
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded	7,500,000		23,100,000	111,600,000
Royalty
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded	3,800,000	1,100,000	7,200,000	1,100,000
Aimmune
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded			9,600,000
Alexion
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded	3,800,000	5,100,000	7,200,000	5,100,000
Astellas
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded	700,000	13,800,000	900,000	13,800,000
Genentech
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded	800,000	$ 600,000	1,500,000	$ 112,500,000
Gilead
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded	7,500,000		13,500,000
MorphoSys
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded			12,500,000
VIR Biotechnology
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded	300,000		$ 300,000
Novartis
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of performance obligations			2
Collaboration and License Agreement | MorphoSys
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue	0		$ 0
Collaboration and License Agreement | Novartis
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 40,100,000		$ 40,100,000
Minimum | Genentech
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Term of revenue recognized			1 year
Maximum | Genentech
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Term of revenue recognized				1 year