Summary of Significant Accounting Policies - Recorded Stock-Based Compensation Expense for Employee and Non-Employee Stock Options and Restricted Stock (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation expense	$ 3,030,000	$ 742,000	$ 371,000
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation expense	2,001,000	605,000	253,000
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation expense	$ 1,029,000	$ 137,000	$ 118,000