Fair Value Measurements - Summary of Changes in Fair Value of Financial Instruments (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2014 USD ($)
Conversion of preferred stock call option liability [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 21
Change in fair value recorded in other income (expense), net	9,560
Conversion of preferred stock into common stock and reclassification to permanent equity	(9,581)
Conversion of preferred stock warrant liability [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	474
Change in fair value recorded in other income (expense), net	2,278
Conversion of preferred stock into common stock and reclassification to permanent equity	$ (2,752)