Income Tax Matters, Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax provision	$ 7.3	$ 7.8	$ 17.1	$ 13.7
Effective tax rate (percent)	27.00%	28.00%	27.00%	23.00%
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount		$ (0.3)	$ (0.5)	$ (2.0)
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Percent		(1.00%)	(1.00%)	(3.00%)
Effective tax rate reconciliation, increase (decrease) to the valuation allowance for certain state net operating losses		$ 0.3	$ 0.8	$ (0.5)
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		$ 0.4
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	$ 0.9	$ 1.2
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent	2.00%	2.00%	2.00%	2.00%
Effective Tax Rate Reconciliation, Unrecognized Tax Benefit Amount	$ 0.2
Effective Income Tax Rate Reconciliation, Unrecognized Tax Benefit 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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