Investments (Details) (USD $)																										3 Months Ended		6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Available-for-sale securities	Dec. 31, 2011 Available-for-sale securities	Jun. 30, 2012 Corporate bonds	Dec. 31, 2011 Corporate bonds	Jun. 30, 2012 Money market funds and deposit accounts	Dec. 31, 2011 Money market funds and deposit accounts	Jun. 30, 2012 Money market funds and deposit accounts Denominated in Euros	Jun. 30, 2012 Money market funds and deposit accounts Denominated in Canadian dollars	Jun. 30, 2012 Enhanced cash mutual fund	Jun. 30, 2012 Collateralized mortgage obligations	Dec. 31, 2011 Collateralized mortgage obligations	Jun. 30, 2012 Fixed rate municipal notes and bonds	Dec. 31, 2011 Fixed rate municipal notes and bonds	Jun. 30, 2012 U.S. Government agency securities	Dec. 31, 2011 U.S. Government agency securities	Jun. 30, 2012 U.S. Treasury securities	Dec. 31, 2011 U.S. Treasury securities	Jun. 30, 2012 Emerging markets debt mutual fund	Dec. 31, 2011 Emerging markets debt mutual fund	Jun. 30, 2012 Asset backed debt securities	Dec. 31, 2011 Asset backed debt securities	Jun. 30, 2012 Other	Dec. 31, 2011 Other	Jun. 30, 2012 Trading securities	Jul. 02, 2011 Trading securities	Jun. 30, 2012 Trading securities	Jul. 02, 2011 Trading securities	Jun. 30, 2012 High yield trading debt securities	Dec. 31, 2011 High yield trading debt securities	Jun. 30, 2012 Emerging markets trading debt mutual fund	Dec. 31, 2011 Emerging markets trading debt mutual fund	Jun. 30, 2012 Emerging markets trading debt securities	Dec. 31, 2011 Emerging markets trading debt securities	Jun. 30, 2012 Other trading debt securities	Dec. 31, 2011 Other trading debt securities
Investments
Unrealized (losses) gain related to trading securities																										$ (135,000)	$ (203,000)	$ 656,000	$ 1,366,000
Amortized Cost			411,142,000	297,916,000	134,965,000	88,589,000	101,011,000	139,420,000			50,000,000	24,859,000	14,915,000	23,553,000	17,718,000	22,424,000	9,720,000	20,458,000	4,848,000	17,693,000	17,693,000	15,499,000	3,533,000	680,000	1,480,000
Fair Value			412,207,000	297,443,000	136,258,000	89,146,000	101,011,000	139,420,000	5,214,000	6,106,000	50,072,000	24,944,000	15,011,000	23,592,000	17,788,000	22,572,000	9,757,000	20,526,000	4,905,000	17,035,000	16,399,000	15,514,000	3,533,000	683,000	1,484,000
Amortized Cost																														21,129,000	20,155,000	2,966,000	2,620,000	2,004,000	2,444,000	684,000	218,000
Fair Value																														22,084,000	20,750,000	2,919,000	2,487,000	2,073,000	2,355,000	754,000	221,000
Total short-term investments, amortized cost	437,925,000	323,353,000
Total short-term investments, fair value	440,037,000	323,256,000
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	44,983,000
Due after one year through three years	88,072,000
Due after three years	67,516,000
Total fixed rate securities	$ 200,571,000