Comprehensive Income (Schedule of Comprehensive Income) (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net income	$ 47,921	$ 38,123	$ 98,538	$ 79,001
Foreign currency translation adjustments	1,782	(3,094)	4,388	(4,880)
Change in unrealized gain (loss) on investments, net	1,580	3,980	2,677	3,989
Income tax expense related to unrealized gain (loss) on investments, net	(605)	(1,542)	(1,025)	(1,545)
Other comprehensive income (loss)	2,757	(656)	6,040	(2,436)
Comprehensive income	$ 50,678	$ 37,467	$ 104,578	$ 76,565