Equity Incentive Plans - Summary of Stock-Based Compensation Expense Related to Equity Incentive Rewards (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation cost	$ 4,343	$ 3,190	$ 11,432	$ 9,015
Common Stock Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation cost			512	483
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation cost	3,386	$ 3,190	9,963	$ 8,532
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation cost	2		2
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation cost	$ 955		$ 955