Stock Incentive Plans - Employee Stock Purchase Plan (Narrative) (Details) $ in Millions			12 Months Ended
	Jun. 21, 2016 shares	Jun. 20, 2016	Dec. 31, 2019 USD ($) offering_period shares	Dec. 31, 2018 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized and reserved for future issuance (in shares)			40,169,185	5,951,523
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of offering periods under the ESPP | offering_period			2
Term of each offering period		6 months
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		747,406
Number of shares of common stock outstanding (as a percent)	0.01
Number of shares authorized, increase (in shares)			224,717	223,432
Shares of common stock issued to employees under the ESPP (in shares)			17,205
Stock-based compensation expense | $			$ 0.1	$ 0.1