Stockholders' Equity - Common stock awards (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	May 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation expense		$ 3.3	$ 0.2	$ 5.5	$ 5.4
Awards To Newly Hired Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, shares	11,625
Equity-based compensation expense	$ 0.2
Retention Program Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, shares	15,891
Equity-based compensation expense	$ 0.2