Share-Based Payments - Summary of Stock-based Compensation Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	$ 501	$ 390	$ 1,137	$ 429
Research and Development Expense [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	144	375	499	408
General and Administrative Expense [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	$ 357	$ 15	$ 638	$ 21