CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income, as reported	$ 820,678	$ 712,685	$ 546,733
Other comprehensive (loss) income:
Change in foreign currency translation adjustment, net of tax	7,238	(1,178)	(10,425)
Available-for-sale investments:
Change in net unrealized losses	(648)	(193)
Net change in available-for-sale investments	(648)	(193)
Other comprehensive (loss) income	6,590	(1,371)	(10,425)
Comprehensive income	$ 827,268	$ 711,314	$ 536,308