Stock-based Compensation - Vested Stock Options and RSUs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total grant date fair value of stock options and RSUs vested during the period	$ 1,369	$ 662	$ 4,861	$ 3,804
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total grant date fair value of stock options and RSUs vested during the period	794	554	3,287	3,071
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total grant date fair value of stock options and RSUs vested during the period	$ 575	$ 108	$ 1,574	$ 733