Income Taxes - Schedule of Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 23.1	$ 24.3	$ 40.3
State	7.2	5.0	5.9
Total current	30.3	29.3	46.2
Deferred:
Federal	12.3	18.4	2.9
State	3.5	2.5	0.5
Total deferred	15.8	20.9	3.4
Total income tax expense	$ 46.1	$ 50.2	$ 49.6