Fair Value Measurements - Summary of Changes in Fair Value of Common Stock Warrant Liability and Derivative Liability Inputs (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in fair value		$ (1,703)
Reclassification		$ 4,551
Significant Unobservable Inputs Level 3 [Member] | Derivative Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 133
Change in fair value	17
Reclassification	(150)
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
Change in fair value	1,703
Reclassification	$ (4,551)