Income Taxes - Schedule of Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance, January 1 (excluding interest and penalties of $15,392, $13,083 and $13,004, respectively)	$ 78,396	$ 77,280	$ 68,224
Increases in gross unrecognized tax benefits relating to tax positions taken during prior years	1,598	5,891
Increases in gross unrecognized tax benefits relating to tax positions taken during current years	19,823	18,438	22,212
Decreases in gross unrecognized tax benefits relating to tax positions taken during prior years	(2,961)	(5,316)	(621)
Decreases in gross unrecognized tax benefits relating to settlements with tax authorities		(1,706)
Decreases in gross unrecognized tax benefits relating to lapse of the applicable statute of limitations	(18,182)	(16,191)	(12,535)
Balance, December 31 (excluding interest and penalties of $15,136, $15,392 and $13,083, respectively)	$ 78,674	$ 78,396	$ 77,280