Fair Value of Financial Instruments - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 46,362	$ 54,059	$ 35,943	$ 7,942
Total	46,362	54,059
Warrant liability	33	3,219
Total	33	3,219
Active markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	46,362	54,059
Total	46,362	54,059
Fair value, inputs, level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability	33	3,219
Total	$ 33	$ 3,219