Income Tax Matters, Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax provision	$ 8.7	$ 8.2	$ 25.8	$ 21.9
Effective tax rate (percent)	26.00%	27.00%	26.00%	24.00%
Effective Income Tax Rate Reconciliation, Tax Expense (Benefit), Share-based Payment Arrangement, Amount			$ (0.6)	$ (2.0)
Effective Income Tax Rate Reconciliation, Tax Expense (Benefit), Share-based Payment Arrangement, Percent			(1.00%)	(2.00%)
Effective tax rate reconciliation, increase (decrease) to the valuation allowance for certain state net operating losses		$ (0.4)	$ 0.6	$ (0.9)
Effective tax rate reconciliation, increase (decrease) to the valuation allowance for certain state net operating losses (percent)		(1.00%)	1.00%	(1.00%)
Effective Income Tax Rate Reconciliation Sequestration of AMT Credits Amount		$ 0.2		$ 0.6
Effective Income Tax Rate Reconciliation Sequestration of AMT Credits Percent		1.00%		1.00%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount	$ 0.5	$ 0.6	$ 1.5	$ 1.7
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent	2.00%	2.00%	2.00%	2.00%
Effective Income Tax Rate Reconciliation Advance Pricing Agreement, Amount		$ 0.3
Effective Income Tax Rate Reconciliation Advance Pricing Agreement, Percent		1.00%
Gross unrecognized tax benefits	$ 1.7		$ 1.7		$ 1.5
Gross unrecognized tax benefits that would impact effective tax rate	$ 0.6		$ 0.6		$ 0.4

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