Share-Based Payments - Summary of Stock-based Compensation Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	$ 808	$ 326	$ 1,945	$ 755
Research and Development Expense [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	449	307	948	715
General and Administrative Expense [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	$ 359	$ 19	$ 997	$ 40