Income Taxes - Narrative (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Tax Credit Carryforward [Line Items]
Impact of Tax Cuts and Jobs Act	$ (4,800,000)	$ (53,100,000)	$ 0
Provision for income taxes	401,400,000	434,900,000	484,600,000
Benefit attributable to implementation of the Tax Cuts and Jobs Act	(16,800,000)	150,000,000
Impact related to federal deferred taxes	12,700,000	(210,000,000)
Unrecognized tax benefit	21,900,000	27,700,000	$ 17,200,000
Increase in net income from recognition of unrecognized tax benefits	19,800,000	21,700,000
Increase (decrease) in unrecognized tax benefits	(5,800,000)	10,500,000
Interest and penalties, net of tax, included in the provision (benefit) for income taxes	300,000	100,000
Income tax examination, penalties and interest accrued	9,200,000	10,300,000
Valuation allowance	300,000	1,100,000
Tax Year 2013 through 2016
Tax Credit Carryforward [Line Items]
Provision for income taxes		(17,600,000)
State and Local Jurisdiction
Tax Credit Carryforward [Line Items]
Net operating loss carryforwards	300,000	1,100,000
Valuation allowance	$ 0	$ 0