Income Tax Matters, Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Income tax provision	$ 5.9	$ 18.5
Effective tax rate (percent)	18.60%	34.00%
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount	$ (1.8)	$ (1.6)
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Percent	(5.60%)	(2.90%)
Effective tax rate reconciliation, decrease to the valuation allowance for certain state net operating losses	$ 0.8	$ 0.4
Effective tax rate reconciliation, decrease to the valuation allowance for certain state net operating losses (percent)	2.70%	0.80%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount	$ 0.6
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent	1.90%
Gross unrecognized tax benefits	$ 1.5
Gross unrecognized tax benefits that would impact effective tax rate	$ 0.4