Income Taxes - Summary of Variations Between the Effective and Statutory U.S. Federal Income Tax Rates (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal income tax provision at statutory tax rate		$ 48,733	$ 39,836	$ 36,000
State tax provision on income less applicable federal tax benefit		1,271	716	867
Foreign income taxed at different rates		(8,075)	(6,325)	(5,060)
Repatriation of foreign earnings		(1,054)	14	21
Unrecognized tax benefits		(47)	23	1,536
Domestic production activities deduction		(1,339)	(1,633)	(884)
Nontaxable foreign interest income		(2,073)	(2,030)	(2,106)
U.S. tax reform, net impact	[1]	14,807
Change in accounting method for depreciation		(893)
Stock based compensation, excess tax benefits	[2]	(2,254)	(1,878)
U.S. tax credits		(1,204)	(1,100)	(3,465)
Non-deductible expenses and other items, net	[3]	(182)	(5)	(90)
Total		$ 47,690	$ 27,618	$ 26,819
Percentage of Federal income tax provision at statutory tax rate		35.00%	35.00%	35.00%
Percentage of State tax provision on income less applicable federal tax benefit		0.90%	0.60%	0.80%
Percentage of Foreign income taxed at different rates		(5.80%)	(5.60%)	(4.90%)
Percentage of foreign earnings		(0.80%)
Percentage of Unrecognized tax benefits		0.00%		1.50%
Percentage of Domestic production activities deduction		(1.00%)	(1.40%)	(0.90%)
Percentage of Nontaxable foreign interest income		(1.50%)	(1.80%)	(2.00%)
Percentage of U.S. tax reform, net impact	[1]	10.70%
Percentage of Change in accounting method for depreciation		(0.60%)
Percentage of stock based compensation, excess tax benefits	[2]	(1.60%)	(1.70%)
Percentage of U.S. tax credits		(0.90%)	(1.00%)	(3.40%)
Percentage of Non-deductible expenses and other items, net	[3]	(0.10%)	0.20%
Percentage of Total income tax provision		34.30%	24.30%	26.10%

[1] Does not include state tax impacts, which are included in state tax provision on income less applicable federal tax benefit.

[2] Excess tax benefits related to employee share-based payment transactions recognized in 2017 and 2016 resulting from the adoption of ASU No. 2016-9. There is no effect for 2015 because the recognition of excess tax benefits in the tax provision is to be done only on a prospective basis, beginning with the year of adopting the new guidance, which was 2016.

[3] Certain 2016 and 2015 amounts have been reclassified to conform to the current year presentation.