Fair Value Measurements - Roll-Forward of Fair Value of Preferred Stock Warrant Liabilities Categorized as Level 3 (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Remeasurement of convertible preferred stock warrants	$ 91	$ 71
Convertible Preferred Stock Warrants
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	2,865
Remeasurement of convertible preferred stock warrants	(91)
Exercise of preferred stock warrants	(63)
Ending balance	$ 2,711