Income Taxes - U.S. Tax Reform Effects (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax benefit related to net operating loss, CARES Act			$ 7.9
Net tax benefit				$ 11.6
Decrease in tax expense	$ 0.2	$ (1.2)
Deferred tax assets that will not be realized		$ 1.0