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
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Non-cash stock-based compensation			$ 2,362	$ 3,083
Stock-based compensation	859	957	2,362	3,083
Non Cash
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Non-cash stock-based compensation	859	957	2,362	3,083
Non Cash | Stock options and employee stock purchase plan awards | Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Non-cash stock-based compensation	96	172	355	507
Non Cash | Stock options and employee stock purchase plan awards | Selling, General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Non-cash stock-based compensation	225	411	764	1,499
Non Cash | Unvested restricted common stock | Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Non-cash stock-based compensation	90	0	361	0
Non Cash | Unvested restricted common stock | Selling, General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Non-cash stock-based compensation	448	374	882	1,038
Non Cash | Warrants Issued | Selling, General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Non-cash stock-based compensation	0	0	0	39
Cash Based
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	0	0	0	0
Cash Based | Modified Stock Option Awards | Selling, General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	0	0	0	0
Cash Based | Purchase Of Interest | Selling, General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	$ 0	$ 0	$ 0	$ 0