Income Taxes (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Effective income tax rates	(17.90%)	35.70%	29.70%	33.70%
Statutory federal tax rate			35.00%
Reduction in income tax expense	$ 0.1		$ 2.8
Net payable related to spin-off tax liabilities	13.0		13.0		$ 16.3
Liability for income taxes associated with uncertain tax positions	12.8		12.8		18.1
Offsetting tax benefits related to uncertain tax positions	5.4		5.4		5.7
Uncertain tax positions, net	7.4		7.4		12.4
Accrued interest and penalties on uncertain tax positions	$ 4.5		4.5		4.1
Other tax benefits related to interest and penalties of uncertain tax positions			$ 2.0		$ 1.8
Unrecognized tax positions increase decrease, months			It is reasonably possible that the amount of the unrecognized benefit with respect to certain of the Company’s unrecognized tax positions may significantly increase or decrease within the next 12 months. Any such change may be the result of ongoing audits or the expiration of federal and state statutes of limitations for the assessment of taxes.