Income Taxes Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Taxes [Line Items]
Income tax expense (benefit)	$ 45,357			$ 69,829	$ 155,871	$ 190,470
Effective income tax rate reconciliation, percent	21.80%			36.70%	26.10%	37.10%
Tax Cuts and Jobs Act - Provisional
Income Taxes [Line Items]
Income tax expense (benefit)							$ (39,000)
Base Erosion and Anti-Abuse Tax
Income Taxes [Line Items]
Income tax expense (benefit)	$ (2,000)	$ 2,000
Transition Tax For Accumulated Foreign Earnings Provisional
Income Taxes [Line Items]
Income tax expense (benefit)	(800)		$ 1,800
Tax Cuts and Jobs Act
Income Taxes [Line Items]
Tax credits from withholding taxes paid on repatriated foreign earnings	(7,000)
State and Local Jurisdiction
Income Taxes [Line Items]
State income tax refund	$ (4,000)
UNITED STATES
Income Taxes [Line Items]
Effective income tax rate reconciliation, at Federal statutory income tax rate, percent					21.00%	35.00%