Income Taxes - Summary of Reconciliation of the Income Tax Expense (Benefit) at the Statutory Income Tax Rate and the Effective Tax Rate for Income before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income before income tax	$ 1,019,404	$ 293,919	$ 219,107
Income tax at the U.S. statutory federal rate (21% in 2018 and 35% in 2017 and 2016)	214,075	102,872	76,687
Increase (decrease) resulting from:
Foreign rate differential	(2,643)	(2,326)	1,434
State income taxes, net of federal benefit	379		66
U.S. earnings not subject to federal income tax	(208,472)	(98,026)	(84,927)
Equity investments	(46)	3,293	4,297
Change in valuation allowance	(2,668)	(5,391)	(6,104)
Other items, net	302	2,259	1,717
Income tax expense (benefit)	$ 927	$ 2,681	$ (6,830)