Income Taxes - Summary of Liabilities Related to Reserve for Uncertain Tax Positions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Reserve for uncertain tax positions, excluding interest and penalties	$ 173,429	$ 158,818	$ 155,318
Interest and penalties included in “Other liabilities”	18,431	13,702
Reserve for uncertain tax positions, including interest and penalties	$ 191,860	$ 172,520