Stockholders' Equity (Details 2) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Comprehensive Income
Net income	$ 36,943	$ 27,751	$ 71,201	$ 45,945
Net change in unrealized gains and losses related to marketable securities, net of deferred tax benefit of $2,029 and $3,404 for the three months ended June 30, 2011 and 2010, respectively, and $2,702 and $631 for the six months ended June 30, 2011 and 2010, respectively	(3,140)	(5,678)	(5,791)	(1,056)
Reclassification adjustment for amounts included in net income, net of deferred tax benefit of $146 and $96 for the three months ended June 30, 2011 and 2010, respectively, and $186 and $127 for the six months ended June 30, 2011 and 2010, respectively	(236)	(160)	(395)	(212)
Foreign currency translation adjustment	369	(770)	456	(602)
Total comprehensive income	$ 33,936	$ 21,143	$ 65,471	$ 44,075