Deferred Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred Costs [Abstract]
Deferred Costs	$ 18.5	$ 21.2
Amortization of Deferred Charges	$ 5.9	$ 4.8	$ 3.0