Income Taxes - 2017 Tax Act (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
2017 Tax Act
Statutory Corporate tax rate (as a percent)	21.00%	21.00%	21.00%	35.00%
Income tax net benefit	$ 1.1		$ 5.4
Income tax additional tax expense			6.6	$ 55.0
Income tax estimated liability and state income and foreign withholding taxes			$ 12.0	12.5
Deferred tax liability and reduction				$ 1.4
Total toll charge liability	35.4
Total toll charge liability, paid	$ 8.5