Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	$ 15,293	$ 12,929	$ 10,762
Stock-based compensation expense for non-employee awards	58	268	(29)
Total stock-based compensation	15,351	13,197	10,733
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	8,271	6,864	5,954
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	$ 7,022	$ 6,065	$ 4,808