Income Taxes - Schedule Reconciles Difference between U.S. Federal Income Taxes at U.S. Statutory Rate and Our Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Statutory federal income tax rate, Amount									$ 44,499	$ 55,684	$ 48,810
State income tax expense, net of federal income tax benefit									6,767	2,808	3,368
Audits and adjustments, net									2,659	(313)	(1,039)
Change in valuation allowances									60	2,472	3,742
Foreign income taxed at different rates									2,639	(6,057)	(6,611)
U.S. mandatory deemed repatriation									(1,396)	5,625
Adjustment of net deferred tax assets for enacted U.S. federal tax reform									(4,198)	7,738
Research and development credits									(4,132)
Change in U.S. tax law applicable to certain foreign entities											2,577
Non-deductible compensation									1,399	571	518
Other, net									(72)	(113)	3,403
Income tax expense	$ 7,671	$ 11,060	$ 17,977	$ 11,517	$ 26,106	$ 13,025	$ 24,376	$ 4,908	$ 48,225	$ 68,415	$ 54,768
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate									21.00%	35.00%	35.00%
State income tax expense, net of federal income tax benefit, Rate									3.20%	1.80%	2.40%
Audits and adjustments, net, Rate									1.30%	(0.20%)	(0.70%)
Change in valuation allowances, Rate										1.50%	2.70%
Foreign income taxed at different rates, Rate									1.20%	(3.80%)	(4.70%)
U.S. mandatory deemed repatriation, Rate									(0.70%)	3.50%
Adjustment of net deferred tax assets for enacted U.S. federal tax reform, Rate									(2.00%)	4.90%
Research and development credits, Rate									(1.90%)
Change in U.S. tax law applicable to certain foreign entities, Rate											1.80%
Non-deductible compensation, Rate									0.70%	0.40%	0.40%
Other, net, Rate										(0.10%)	2.40%
Effective tax rate									22.80%	43.00%	39.30%