Collaboration and License Agreements - Schedule of Effect of Adopting ASC 606 by Performance Obligation (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	$ 26,401,000	$ 11,346,000	$ 33,746,000	$ 21,854,000
Reduction of research and development expenses	0	2,489,000	0	5,265,000
Under Topic 605
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	25,982,000		35,959,000
Effect of Change | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	419,000		(2,213,000)
Licenses
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	15,000,000		15,000,000
Licenses | Under Topic 605 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	15,000,000		15,000,000
Licenses | Effect of Change | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	0		0
Research and development services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	9,830,000		16,194,000
Research and development services | Under Topic 605 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	9,367,000		18,320,000
Research and development services | Effect of Change | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	463,000		(2,126,000)
Committee participations
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	0		0
Committee participations | Under Topic 605 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	44,000		87,000
Committee participations | Effect of Change | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue - related party	(44,000)		(87,000)
Development services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reduction of research and development expenses	0	$ 2,500,000	0	$ 5,300,000
Development services | Under Topic 605 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reduction of research and development expenses	1,652,000		2,063,000
Development services | Effect of Change | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reduction of research and development expenses	$ (1,652,000)		$ (2,063,000)