Income Taxes - Valuation allowance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Valuation Allowance
Valuation allowance, Balance at beginning of period	$ 35.5	$ 30.8
Valuation allowance, Balance at end of period	26.6	35.5	$ 30.8
Deferred tax assets related primarily to state net operating loss carryforwards
Valuation Allowance
Valuation allowance, Balance at beginning of period	35.5	30.8	26.5
Additions charged to income tax expense and other accounts	0.3	6.6	4.3
Deductions from reserves	(9.2)	(1.9)
Valuation allowance, Balance at end of period	$ 26.6	$ 35.5	$ 30.8