Short- and Long-Term Investments and Investments on Deposit for Licensure (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 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	$ 472,246	$ 352,114
Gross unrealized holding losses, less than twelve months	2,353	2,221
Total number of securities, less than twelve months	147	142
Fair value, twelve months or greater	20,540	21,293
Gross unrealized holding losses, twelve months or greater	1,011	1,357
Total number of securities, twelve months or greater	4	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	11,551	21,293
Gross unrealized holding losses, twelve months or greater	999	1,357
Total number of securities, twelve months or greater	3	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	149,074	19,495
Gross unrealized holding losses, less than twelve months	95	4
Total number of securities, less than twelve months	12	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	185,231	71,278
Gross unrealized holding losses, less than twelve months	1,498	186
Total number of securities, less than twelve months	98	37
Fair value, twelve months or greater	8,989	0
Gross unrealized holding losses, twelve months or greater	12	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	103,766	86,881
Gross unrealized holding losses, less than twelve months	100	465
Total number of securities, less than twelve months	28	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
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	17,021
Gross unrealized holding losses, less than twelve months	658
Total number of securities, less than twelve months	5
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
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	5,129	160,860
Gross unrealized holding losses, less than twelve months	1	1,562
Total number of securities, less than twelve months	1	64
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
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	9,564
Gross unrealized holding losses, less than twelve months	1	1
Total number of securities, less than twelve months	3	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