Income Taxes - comprehensive tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		35.00%	35.00%	35.00%
Provisional net tax expenses		$ 3.6
One-time transition tax on unrepatriated earnings of foreign subsidiaries		0.2
Net expenses due to remeasurement of deferred tax assets		$ 3.4
Scenario, Forecast
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%