Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	$ 886	$ 2,647	$ 2,860
Stock options and ESPP awards | Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	62	131	303
Stock options and ESPP awards | Selling, General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	321	401	837
Unvested restricted common stock | Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	116	576	487
Unvested restricted common stock | Selling, General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	143	1,467	$ 1,233
Restricted stock units | Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	28	10
Restricted stock units | Selling, General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	$ 216	$ 62