Short- and Long-Term Investments and Investments on Deposit for Licensure (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 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	$ 153,188	$ 472,246
Gross unrealized holding losses, less than twelve months	684	2,353
Total number of securities, less than twelve months	120	147
Fair value, twelve months or greater	12,605	20,540
Gross unrealized holding losses, twelve months or greater	546	1,011
Total number of securities, twelve months or greater	5	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	68,680	185,231
Gross unrealized holding losses, less than twelve months	123	1,498
Total number of securities, less than twelve months	68	98
Fair value, twelve months or greater	6,861	8,989
Gross unrealized holding losses, twelve months or greater	40	12
Total number of securities, twelve months or greater	3	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	19,719	103,766
Gross unrealized holding losses, less than twelve months	80	100
Total number of securities, less than twelve months	11	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	11,353	17,021
Gross unrealized holding losses, less than twelve months	394	658
Total number of securities, less than twelve months	6	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	39,325	5,129
Gross unrealized holding losses, less than twelve months	85	1
Total number of securities, less than twelve months	30	1
Fair value, twelve months or greater	5,744	11,551
Gross unrealized holding losses, twelve months or greater	506	999
Total number of securities, twelve months or greater	2	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	14,111	12,025
Gross unrealized holding losses, less than twelve months	2	1
Total number of securities, less than twelve months	5	3
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