Investments (Details) (USD $) In Thousands, unless otherwise specified																								3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Available-for-sale securities	Dec. 31, 2011 Available-for-sale securities	Mar. 31, 2012 Corporate bonds	Dec. 31, 2011 Corporate bonds	Mar. 31, 2012 Money market funds	Dec. 31, 2011 Money market funds	Mar. 31, 2012 Money market funds Denominated in Euros	Mar. 31, 2012 U.S. Treasury securities	Dec. 31, 2011 U.S. Treasury securities	Mar. 31, 2012 Collateralized mortgage obligations	Dec. 31, 2011 Collateralized mortgage obligations	Mar. 31, 2012 Fixed rate municipal notes and bonds	Dec. 31, 2011 Fixed rate municipal notes and bonds	Mar. 31, 2012 U.S. Government agency securities	Dec. 31, 2011 U.S. Government agency securities	Mar. 31, 2012 Emerging markets debt mutual fund	Dec. 31, 2011 Emerging markets debt mutual fund	Mar. 31, 2012 Asset backed debt securities	Dec. 31, 2011 Asset backed debt securities	Mar. 31, 2012 Other	Dec. 31, 2011 Other	Mar. 31, 2012 Trading securities	Apr. 02, 2011 Trading securities	Mar. 31, 2012 High yield trading debt securities	Dec. 31, 2011 High yield trading debt securities	Mar. 31, 2012 Emerging markets trading debt mutual fund	Dec. 31, 2011 Emerging markets trading debt mutual fund	Mar. 31, 2012 Emerging markets trading debt securities	Dec. 31, 2011 Emerging markets trading debt securities	Mar. 31, 2012 Other trading debt securities	Dec. 31, 2011 Other trading debt securities
Investments
Unrealized (losses) gain related to trading securities																								$ 828	$ 330
Amortized Cost			330,892	297,916	132,726	88,589	69,867	139,420		36,110	4,848	22,677	14,915	21,275	17,718	18,534	9,720	17,693	17,693	10,530	3,533	1,480	1,480
Fair Value			332,315	297,443	133,989	89,146	69,867	139,420	19,419	36,095	4,905	22,720	15,011	21,335	17,788	18,603	9,757	17,687	16,399	10,536	3,533	1,483	1,484
Amortized Cost																										21,217	20,155	2,651	2,620	2,099	2,444	217	218
Fair Value																										22,349	20,750	2,686	2,487	2,246	2,355	238	221
Total short-term investments, amortized cost	357,076	323,353
Total short-term investments, fair value	359,834	323,256
Estimated fair value of fixed rate securities designated as available-for-sale, classified by the contractual maturity date of the security
Due within one year	53,083
Due after one year through three years	90,771
Due after three years	66,844
Total fixed rate securities	$ 210,698