Stock-based Compensation Details 9 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based Compensation Expense	$ 11.4	$ 7.7	$ 6.7
Performance-Based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Stock-based Compensation Expense	$ 2.7	$ 1.5	$ 1.0
Performance-Based Restricted Stock Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PercentageOfUnitsEarnedOfUnitsGranted	0.00%
Performance-Based Restricted Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PercentageOfUnitsEarnedOfUnitsGranted	200.00%
Executive Officer [Member] | Performance-Based Restricted Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PercentageOfUnitsEarnedOfUnitsGranted	100.00%