Revenue Recognition - Schedule of Revenue Affected by Adopting ASC 606 (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Research and development revenues	$ 8,726		$ 16,991
License Revenues [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License revenues	1,915	$ 318	5,133	$ 6,706
Calculated Under Revenue Guidance in Effect Before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Research and development revenues	(872)		(2,206)
Calculated Under Revenue Guidance in Effect Before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | License Revenues [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License revenues	4,954		12,901
Difference Between Revenue Guidance in Effect Before and After Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Research and development revenues	9,598		19,197
Difference Between Revenue Guidance in Effect Before and After Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | License Revenues [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License revenues	$ (3,039)		$ (7,768)