Income Taxes - Components of Income before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
United States	$ 813,078	$ 934,476	$ 1,004,919
Foreign	196,190	139,864	118,762
Income before income taxes	$ 1,009,268	$ 1,074,340	$ 1,123,681	$ 1,117,739	$ 1,044,304