Fair Value Measurements - Summary of Changes in Fair Value of Common Stock Warrant Liability and Derivative Liability Inputs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 2,848
Change in fair value	(1,703)	$ (2,155)	$ 1,789
Reclassification	4,551
Ending Balance		2,848
Significant Unobservable Inputs Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	2,848
Ending Balance		2,848
Significant Unobservable Inputs Level 3 [Member] | Derivative Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	133	126
Initial fair value of derivative			130
Change in fair value	17	7	(4)
Reclassification	(150)
Ending Balance		133	126
Common Stock Warrant Liability [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	2,848	693	2,482
Change in fair value	1,703	2,155	(1,789)
Reclassification	$ (4,551)
Ending Balance		$ 2,848	$ 693