Income Tax Matters, Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax provision	$ 16.1	$ 9.4	$ 36.8	$ 40.2
Effective tax rate (percent)	44.70%	38.70%	37.80%	37.50%
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount	$ 2.5		$ 2.5
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	7.10%		2.60%
Effective tax rate reconciliation, decrease due to recognition of excess tax benefits from stock-based compensation			$ (1.7)
Effective tax rate reconciliation, decrease due to recognition of excess tax benefits from stock-based compensation (percent)			(1.70%)
Effective tax rate reconciliation, decrease to the valuation allowance for certain state net operating losses			$ (0.5)
Effective tax rate reconciliation, decrease to the valuation allowance for certain state net operating losses (percent)			(0.60%)
Effective tax rate reconciliation, decrease related to unrecognized tax benefits , including interest and penalties			$ (0.2)
Effective tax rate reconciliation, decrease related to unrecognized tax benefits , including interest and penalties (percent)			(0.20%)
Gross unrecognized tax benefits	$ 1.5		$ 1.5		$ 1.8
Gross unrecognized tax benefits that would impact effective tax rate	$ 0.4		$ 0.4		$ 0.7