Stock Incentive Plans - Employee Stock Purchase Plan (Narrative) (Details) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 21, 2016 shares	Jun. 30, 2020 USD ($) shares	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) offering_period shares	Jun. 30, 2019 USD ($) shares	Dec. 31, 2019 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized and reserved for future issuance (in shares)		27,757,227		27,757,227		40,169,185
Stock-based compensation expense | $		$ 1,481	$ 1,251	$ 2,890	$ 2,431
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of offering periods under the ESPP | offering_period				2
Eligible compensation withheld for use (up to) (as a percent)	25.00%
Purchase price of shares (not less than) (as a percent)	85.00%
Common stock authorized and reserved for future issuance (in shares)	173,076	1,532,077		1,532,077
Number of shares of common stock outstanding (as a percent)	0.01
Number of shares authorized, increase (in shares)				863,254	224,717
Shares of common stock issued to employees under the ESPP (in shares)				78,583
Stock-based compensation expense | $				$ 100	$ 100