Stock-Based Compensation - Performance-based Awards (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	May 31, 2019	Jan. 31, 2019	Dec. 31, 2018	Jun. 30, 2017
Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved								425,000
Performance-based awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved							600,000
Stock-based compensation expense	$ 2.5		$ 2.5
Performance-based awards | Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved						200,000		200,000
Stock-based compensation expense	0.4	$ 0.1	0.6	$ 0.4
Restricted stock units | Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved						100,000
Stock-based compensation expense	0.3		0.5
Restricted stock units | Chief Financial Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved						100,000
Stock-based compensation expense			1.0
Restricted stock units | Chief Operating Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved						100,000
Restricted stock units | Chief Financial Officer and Chief Operating Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	0.7
Restricted stock units | Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares approved					188,099
Stock-based compensation expense	$ 0.9		$ 0.9