Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense for employee awards	$ 10,762	$ 6,744	$ 6,472
Stock-based compensation expense for non-employee awards	(29)	145	480
Total stock-based compensation expense	10,733	6,889	6,952
Research and Development Expense [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense for employee awards	5,954	4,234	3,597
General and Administrative Expense [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense for employee awards	$ 4,808	$ 2,510	$ 2,875