Income Taxes - Summary of Effective Income Tax Rate Differs from Amount Computed by Applying U.S. Federal Statutory Income Tax Rate to Income Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Income Tax Disclosure [Abstract]
Expected tax expense	$ 12,678	$ 29,762		$ 29,361
Change in valuation allowance	0	(21)		22
Impact of tax holiday	(5,448)	(4,396)		(4,027)
Foreign tax rate differential	5,014	(2,616)		(2,716)
Deferred tax (benefit)/provision	(3,915)	(1,887)		(878)
Unrecognized tax benefits and interest	(88)	(3,905)		495
State taxes, net of Federal taxes	2,200	339		202
Non-deductible expenses	3,066	825		144
US Tax Reform Act impact	176	29,185		0
Excess tax benefit on stock-based compensation	(7,227)	(9,797)		0
Research & Development credit	(1,500)	(844)		(890)
Other	(1,559)	(499)		438
Income tax expense	$ 3,397	$ 36,146	[1]	$ 22,151	[1]

[1] Adjusted pursuant to adoption of ASU No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Post-retirement Benefit Cost. Refer to Note 21 and Note 27 to the consolidated financial statements.