Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Consolidated Statements of Comprehensive Income [Abstract]
Net Income	$ 21,070	$ 36,943	$ 34,031	$ 71,201
Other Comprehensive Income (Loss), net of tax:
Net change in unrealized gains (losses) on marketable securities	(5,054)	(3,140)	1,701	(5,791)
Reclassification adjustments for amounts included in net income	(181)	(236)	(179)	(395)
Foreign currency translation	(96)	369	58	456
Other Comprehensive Income (Loss), net of tax	(5,331)	(3,007)	1,580	(5,730)
Comprehensive Income, net of tax	$ 15,739	$ 33,936	$ 35,611	$ 65,471