Fair Value Measurements - Reconciliation of Liabilities Measured at Fair Value Using Level 3 Significant Unobservable Inputs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value Disclosures [Abstract]
Balance, beginning of period	$ 2,460	$ 2,773
Issuance of preferred stock warrants		868
Reclassification of stock award liability from additional paid-in capital upon modification		399
Reclassification of stock award liability to additional paid-in capital upon expiration		(292)
Change in fair value of stock award liability		(107)
Reclassification of preferred stock warrant liability to additional paid-in capital upon conversion to common stock	(521)
Change in fair value of preferred stock warrant liabilities	$ (1,939)	(1,181)	$ (272)
Balance, end of period		$ 2,460	$ 2,773