Income Taxes - Summary of Provision for Income Taxes and U.S. Federal Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Computed “expected” tax expense	$ 312,756	$ 225,022	$ 187,601
Change in valuation allowance	18,289	11,952	20,243
Foreign income tax differential	(38,695)	(25,533)	(23,718)
State taxes net of federal benefits	12,884	9,439	6,711
Foreign-sourced nontaxable income	(8,836)	(13,659)	(10,573)
IRC Section 199 deduction	(8,844)	(7,731)	(10,221)
Excess tax benefits related to stock-based compensation	(18,058)	(11,974)	0
Subpart F income/transition tax - federal only	195,779	0	0
Foreign tax credit/transition tax - federal only	(113,955)	0	0
Tax reform - federal rate reduction	(209,966)	0	0
Other	12,036	3,018	3,530
Total provision	$ 153,390	$ 190,534	$ 173,573
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Percent [Abstract]
Computed "expected" tax expense, rate	35.00%	35.00%	35.00%
Change in valuation allowance, rate	2.00%	1.90%	3.80%
Foreign income tax differential, rate	(4.30%)	(4.00%)	(4.40%)
State taxes net of federal benefits, rate	1.40%	1.50%	1.20%
Foreign-sourced nontaxable income, rate	(1.00%)	(1.20%)	(2.00%)
IRC Section 199 deduction, rate	(1.00%)	(1.20%)	(1.90%)
Excess tax benefits related to stock-based compensation, rate	(2.00%)	(1.90%)	0.00%
Subpart F income/transition tax - federal only, rate	21.90%	0.00%	0.00%
Foreign tax credit/transition tax - federal only, rate	(12.80%)	(0.00%)	(0.00%)
Tax reform - federal rate reduction, rate	(23.50%)	0.00%	0.00%
Other, rate	1.30%	(0.40%)	0.70%
Provision for income taxes, rate	17.20%	29.70%	32.40%