Fair Value of Financial Instruments - Summary of Financial Instruments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Series A Warrant Liability [Member]
Liabilities
Warrant liability	$ 558	$ 1,213
Series C Warrant Liability [Member]
Liabilities
Warrant liability	219	462
Fair Value, Measurements, Recurring [Member]
Liabilities
Warrant liability	777	2,540
Fair Value, Measurements, Recurring [Member] | Convertible preferred stock warrant liability [Member] | Series A Warrant Liability [Member]
Liabilities
Warrant liability	558	1,213
Fair Value, Measurements, Recurring [Member] | Convertible preferred stock warrant liability [Member] | Series B Warrant Liability [Member]
Liabilities
Warrant liability		865
Fair Value, Measurements, Recurring [Member] | Convertible preferred stock warrant liability [Member] | Series C Warrant Liability [Member]
Liabilities
Warrant liability	219	462
Fair Value, Measurements, Recurring [Member] | Money market fund [Member]
Assets
Cash and cash equivalents	3,975	3,804
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Liabilities
Warrant liability	558	1,213
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Convertible preferred stock warrant liability [Member] | Series A Warrant Liability [Member]
Liabilities
Warrant liability	558	1,213
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Money market fund [Member]
Assets
Cash and cash equivalents	3,975	3,804
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Liabilities
Warrant liability	219	1,327
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Convertible preferred stock warrant liability [Member] | Series B Warrant Liability [Member]
Liabilities
Warrant liability		865
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Convertible preferred stock warrant liability [Member] | Series C Warrant Liability [Member]
Liabilities
Warrant liability	$ 219	$ 462