Share-Based Payments - Summary of Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	$ 629	$ 808	$ 1,895	$ 1,945
Research and development expense
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	272	449	770	948
General and administrative expense
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	$ 357	$ 359	$ 1,125	$ 997