Fair Value Measurements - Roll-Forward of Fair Value of Preferred Stock Warrant Liabilities Categorized as Level 3 (Details) - 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]
Remeasurement of convertible preferred stock warrants	$ 559	$ 703	$ (398)
Convertible Preferred Stock Warrants
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	2,865	3,568	3,170
Remeasurement of convertible preferred stock warrants	(559)	(703)	398
Exercise of preferred stock warrants	(1,801)
Conversion of preferred stock warrants into common stock warrants at initial public offering	$ (505)
Ending balance		$ 2,865	$ 3,568