Income Taxes - Schedule of Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Deferred Tax Liabilities, Unrealized Gains on Trading Securities	$ 0.0
Current:
Federal	39.4	$ 42.4	$ 40.5
State	11.3	12.3	8.2
Total current	50.7	54.7	48.7
Deferred:
Federal	3.7	(5.7)	3.7
State	1.3	(0.9)	1.7
Total deferred	5.0	(6.6)	5.4
Total income tax expense	55.7	48.1	54.1
Operating Loss Carryforwards [Line Items]
Benefit of stock-based compensation plans			(1.2)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount	0.8	0.0	$ 0.2
Common Stock Including Additional Paid in Capital [Member]
Operating Loss Carryforwards [Line Items]
Benefit of stock-based compensation plans	$ (0.5)	$ (0.4)