Short- and Long-Term Investments and Investments on Deposit for Licensure (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012 Securities	Dec. 31, 2011 Securities
Schedule of available-for-sale securities with unrealized losses not deemed to be other-than-temporarily impaired
Fair value, less than twelve months	$ 68,302	$ 472,246
Gross unrealized holding losses, less than twelve months	223	2,353
Total number of securities, less than twelve months	58	147
Fair value, twelve months or greater	2,556	20,540
Gross unrealized holding losses, twelve months or greater	269	1,011
Total number of securities, twelve months or greater	1	4
Commercial paper [Member]
Schedule of available-for-sale securities with unrealized losses not deemed to be other-than-temporarily impaired
Fair value, less than twelve months		149,074
Gross unrealized holding losses, less than twelve months		95
Total number of securities, less than twelve months		12
Fair value, twelve months or greater		0
Gross unrealized holding losses, twelve months or greater		0
Total number of securities, twelve months or greater		0
Corporate bonds [Member]
Schedule of available-for-sale securities with unrealized losses not deemed to be other-than-temporarily impaired
Fair value, less than twelve months	21,179	185,231
Gross unrealized holding losses, less than twelve months	27	1,498
Total number of securities, less than twelve months	35	98
Fair value, twelve months or greater	0	8,989
Gross unrealized holding losses, twelve months or greater	0	12
Total number of securities, twelve months or greater	0	1
Debt securities of government sponsored entities [Member]
Schedule of available-for-sale securities with unrealized losses not deemed to be other-than-temporarily impaired
Fair value, less than twelve months	5,625	103,766
Gross unrealized holding losses, less than twelve months	6	100
Total number of securities, less than twelve months	5	28
Fair value, twelve months or greater	0	0
Gross unrealized holding losses, twelve months or greater	0	0
Total number of securities, twelve months or greater	0	0
Equity index funds [Member]
Schedule of available-for-sale securities with unrealized losses not deemed to be other-than-temporarily impaired
Fair value, less than twelve months	4,646	17,021
Gross unrealized holding losses, less than twelve months	104	658
Total number of securities, less than twelve months	2	5
Fair value, twelve months or greater	0	0
Gross unrealized holding losses, twelve months or greater	0	0
Total number of securities, twelve months or greater	0	0
Municipal bonds [Member]
Schedule of available-for-sale securities with unrealized losses not deemed to be other-than-temporarily impaired
Fair value, less than twelve months	36,852	5,129
Gross unrealized holding losses, less than twelve months	86	1
Total number of securities, less than twelve months	16	1
Fair value, twelve months or greater	2,556	11,551
Gross unrealized holding losses, twelve months or greater	269	999
Total number of securities, twelve months or greater	1	3
U.S. Treasury securities [Member]
Schedule of available-for-sale securities with unrealized losses not deemed to be other-than-temporarily impaired
Fair value, less than twelve months		12,025
Gross unrealized holding losses, less than twelve months		1
Total number of securities, less than twelve months		3
Fair value, twelve months or greater		0
Gross unrealized holding losses, twelve months or greater		$ 0
Total number of securities, twelve months or greater		0