Short- and Long-Term Investments and Investments on Deposit for Licensure (Details 3) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Schedule of available-for-sale securities with unrealized losses not deemed to be other-than-temporarily impaired
Fair value, less than twelve months	$ 184,614	$ 352,114
Gross unrealized holding losses, less than twelve months	602	2,221
Total number of securities, less than twelve months	54	142
Fair value, twelve months or greater	26,567	21,293
Gross unrealized holding losses, twelve months or greater	1,186	1,357
Total number of securities, twelve months or greater	6	6
Auction Rate 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	0	0
Gross unrealized holding losses, less than twelve months	0	0
Total number of securities, less than twelve months	0	0
Fair value, twelve months or greater	15,672	21,293
Gross unrealized holding losses, twelve months or greater	1,078	1,357
Total number of securities, twelve months or greater	4	6
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	17,985	19,495
Gross unrealized holding losses, less than twelve months	6	4
Total number of securities, less than twelve months	1	8
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
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	50,231	71,278
Gross unrealized holding losses, less than twelve months	70	186
Total number of securities, less than twelve months	22	37
Fair value, twelve months or greater	8,983	0
Gross unrealized holding losses, twelve months or greater	5	0
Total number of securities, twelve months or greater	1	0
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	71,396	86,881
Gross unrealized holding losses, less than twelve months	198	465
Total number of securities, less than twelve months	18	29
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
Federally insured 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		4,036
Gross unrealized holding losses, less than twelve months		3
Total number of securities, less than twelve months		1
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
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	45,002	160,860
Gross unrealized holding losses, less than twelve months	328	1,562
Total number of securities, less than twelve months	13	64
Fair value, twelve months or greater	1,912	0
Gross unrealized holding losses, twelve months or greater	103	0
Total number of securities, twelve months or greater	1	0
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		9,564
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