Income Taxes Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Valuation Allowance [Line Items]
Interest Related to Uncertain Tax Positions	$ 0.0	$ 4.1	$ 0.7
Reduction In General And Administrative Expense Due To Uncertain Tax Positions Realized		$ 2.5
Federal statutory income tax rate	21.00%	21.00%	21.00%	35.00%
Operating Loss Carryforwards, Valuation Allowance	$ 101.9	$ 98.8
Alternative Minimum Tax Credit Refund Received	170.7	73.9
Alternative minimum tax		126.0
Unrecognized Tax Benefits	0.0	$ 0.0	$ 19.0
AMT Credit Refunds Receivable	61.6
Other Current Assets [Member]
Valuation Allowance [Line Items]
AMT Credit Refunds Receivable	30.7
Other Noncurrent Assets [Member]
Valuation Allowance [Line Items]
AMT Credit Refunds Receivable	$ 30.9