Income Tax Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 01, 2016
Federal Income Tax Note
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Deferred Tax Liability, Provisional Income Tax Benefit	$ 97.9
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Transition Tax for Accumulated Foreign Earnings, Provisional Income Tax Expense	$ 66.4
Tax Cuts and Jobs Act of 2017, Accounting Complete	false
Income Tax Benefit from Enacted Tax Rate Changes		$ 4.5	$ 6.5
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Undistributed Accumulated Earnings of Foreign Subsidiary for which Unrecognized Deferred Tax Liabilities Have not Been Recorded	$ 700.0
Unrecognized Tax Benefits, Interest on Income Taxes Expense			1.0
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority			6.8
Operating Loss Carryforwards	0.0	1.3		$ 2.5
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	0.0	0.6		$ 0.6
Valuation Allowance on Deferred Tax Assets	20.3	17.2
Deferred Tax Assets, State Taxes	22.0	18.7
Income Taxes Paid, Net	377.0	384.3	$ 189.1
State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards	160.0
Valuation Allowance on Deferred Tax Assets	$ 19.3	$ 16.3
Minimum | State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2018
Maximum | State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037
Capital Loss Carryforward
Federal Income Tax Note
Tax Credit Carryforward, Amount	$ 0.7
Tax Credit Carryforward, Expiration Date	Dec. 31, 2022