Income Taxes Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Taxes [Line Items]
Income Tax Expense (Benefit)	$ 48,958		$ 65,055	$ 110,514	$ 120,641
Effective Income Tax Rate Reconciliation, Percent	25.80%		37.40%	28.50%	37.40%
Tax Cuts and Jobs Act - Provisional
Income Taxes [Line Items]
Income Tax Expense (Benefit)						$ (39,000)
Transition Tax For Accumulated Foreign Earnings
Income Taxes [Line Items]
Income Tax Expense (Benefit)		$ 1,800
Base Erosion and Anti-Abuse Tax
Income Taxes [Line Items]
Income Tax Expense (Benefit)	$ 2,000
UNITED STATES
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				21.00%	35.00%