Income Taxes - Reconciliation of Tax Expense at Effective Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Expense, Continuing Operations Income Tax Reconciliation [Abstract]
Tax expense at the statutory tax rate	$ 54.0	$ 52.0	$ 44.0
Increase (decrease) in tax resulting from:
Tax-exempt income	(8.4)	(2.8)	(2.1)
State income tax, net of federal income tax benefit	10.6	9.9	9.0
Deficiency (benefit) of stock-based compensation plans	0.2	(0.5)	(0.4)
Federal tax credits	(4.3)	(4.3)	(2.3)
Other, net	0.8	0.6	(0.1)
Total income tax expense	$ 54.9	$ 55.7	$ 48.1