Income Tax Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Rate	Dec. 31, 2015 USD ($) Rate	Dec. 31, 2014 USD ($)	Aug. 01, 2016 USD ($)
Federal Income Tax Note
2020 UK Tax Rate | Rate	17.00%
2015 UK Tax Rate | Rate		20.00%
2017 UK Tax Rate | Rate		19.00%
2020 UK Tax Rate Prior to 2016 Enactment | Rate		18.00%
Income Tax Benefit from Enacted Tax Rate Changes	$ 4,500,000	$ 6,500,000
Excess of Financial Reporting Carrying Amount Over the Tax Basis of Investments in Foreign Subsidiaries, Provision Not Practicable	1,000,000,000
Tax Expense Not Recognized Due To Permanent Differences	200,000,000
Liability for unrecognized tax benefits			$ 10,400,000
Unrecognized Tax Benefits, Interest on Income Taxes Expense		(1,000,000)	200,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued			1,000,000
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority		(6,800,000)
Operating Loss Carryforwards	$ 1,300,000			$ 2,500,000
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax				$ 600,000
Net Operating Loss Benefit	1,200,000
Valuation Allowance on Deferred Tax Assets	$ 17,200,000	1,300,000
Deferred Tax Assets, State Taxes	18,700,000
Income Taxes Paid, Net	384,300,000	$ 189,100,000	$ 155,700,000
State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards	160,000,000
Valuation Allowance on Deferred Tax Assets	$ 16,300,000
Minimum
Federal Income Tax Note
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2023
Minimum | State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2017
Maximum
Federal Income Tax Note
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2035
Maximum | State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2036
Other Comprehensive Income (Loss) | State and Local Jurisdiction
Federal Income Tax Note
Valuation Allowance on Deferred Tax Assets	$ 1,500,000