Income Taxes - Effective Income Tax Rate Reconciliation, Amount (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Statutory U.S. federal income tax	$ 41.0	$ 37.9	$ 40.3
State income taxes, net of federal benefit	11.9	9.1	10.9
Reserve adjustments	0.1	1.2	3.9
Nondeductible compensation	1.6	3.4	1.0
Tax credits and special deductions	0.6	(4.6)	(2.7)
Convertible debt	(3.4)	0.0	0.0
Stock-based compensation excess tax benefits	(1.0)	(4.4)	(2.3)
Other	0.5	(0.1)	(0.2)
Income tax provision	$ 51.3	$ 42.5	$ 50.9