Income Taxes (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Effective income tax rates	22.50%	18.20%
Federal income tax rates	21.00%	21.00%
Net payable related to spin-off tax liabilities	$ 15.8		$ 15.6
Liability for income taxes associated with uncertain tax positions	13.4		13.3
Offsetting tax benefits related to uncertain tax positions	3.7		3.7
Uncertain tax positions, net	9.7		9.6
Accrued interest and penalties on uncertain tax positions	6.0		5.8
Other tax benefits related to interest and penalties of uncertain tax positions	$ 1.7		$ 1.6
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 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.