Summary of Significant Accounting Policies - Schedule of Impact of Adoption on Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration and license revenue	$ 9,546	$ 8,230
Loss from operations	(9,856)	(6,313)
Net loss	(9,417)	$ (5,996)
Scenario, Previously Reported [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration and license revenue	4,364
Loss from operations	(15,038)
Net loss	(14,599)
Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration and license revenue	5,182
Loss from operations	5,182
Net loss	$ 5,182