Share-Based Payments - Summary of Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	$ 602	$ 501	$ 1,266	$ 1,137
Research and development expense
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	219	144	498	499
General and administrative expense
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total stock-based expenses	$ 383	$ 357	$ 768	$ 638