Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 333,817	$ 331,655	$ 318,713
Other comprehensive loss, net of tax:
Foreign currency translation adjustments	(12,131)	(14,900)	(10,189)
Unrealized holding (loss) gain on investments:
Unrealized holding (losses) gains during the period, net of income taxes of $457, $822 and $(592)	(918)	(1,659)	441
Less: reclassification adjustment for losses (gains) realized in net income, net of income taxes of $(201), $(76) and $319	384	164	(634)
Total other comprehensive loss, net of taxes	(12,665)	(16,395)	(10,382)
Comprehensive income	$ 321,152	$ 315,260	$ 308,331