Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Fair Value Measurements By Level For Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details)

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Fair Value Measurements (Fair Value Measurements By Level For Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Cash and cash equivalents $ 796,621 $ 573,698
U.S. Treasury securities and obligations of U.S. government corporations and agencies 46,463 22,486
Corporate securities 262,999 189,029
Municipal securities, General obligation 92,908 129,608
Municipal securities, Pre-refunded 16,659 33,712
Municipal securities, Revenue 87,060 120,860
Municipal securities, Variable rate demand notes 92,225 64,658
Asset backed securities 75,420 52,192
Total investments 673,734 612,545
Cash and cash equivalents 13,150 13,775
Certificates of deposit 5,891 5,890
U.S. Treasury securities and obligations of U.S. government corporations and agencies 14,468 7,153
Total restricted deposits 33,509 26,818
Interest rate swap contract 17,196 11,431
Total assets at fair value 1,521,060 1,224,492
Level I [Member]
   
Cash and cash equivalents 796,621 573,698
U.S. Treasury securities and obligations of U.S. government corporations and agencies 34,409 17,091
Corporate securities 0 0
Municipal securities, General obligation 0 0
Municipal securities, Pre-refunded 0 0
Municipal securities, Revenue 0 0
Municipal securities, Variable rate demand notes 0 0
Asset backed securities 0 0
Total investments 34,409 17,091
Cash and cash equivalents 13,150 13,775
Certificates of deposit 5,891 5,890
U.S. Treasury securities and obligations of U.S. government corporations and agencies 13,958 7,153
Total restricted deposits 32,999 26,818
Interest rate swap contract 0 0
Total assets at fair value 864,029 617,607
Level II [Member]
   
Cash and cash equivalents 0 0
U.S. Treasury securities and obligations of U.S. government corporations and agencies 12,054 5,395
Corporate securities 262,999 189,029
Municipal securities, General obligation 92,908 129,608
Municipal securities, Pre-refunded 16,659 33,712
Municipal securities, Revenue 87,060 120,860
Municipal securities, Variable rate demand notes 92,225 64,658
Asset backed securities 75,420 52,192
Total investments 639,325 595,454
Cash and cash equivalents 0 0
Certificates of deposit 0 0
U.S. Treasury securities and obligations of U.S. government corporations and agencies 510 0
Total restricted deposits 510 0
Interest rate swap contract 17,196 11,431
Total assets at fair value 657,031 606,885
Level III [Member]
   
Cash and cash equivalents 0 0
U.S. Treasury securities and obligations of U.S. government corporations and agencies 0 0
Corporate securities 0 0
Municipal securities, General obligation 0 0
Municipal securities, Pre-refunded 0 0
Municipal securities, Revenue 0 0
Municipal securities, Variable rate demand notes 0 0
Asset backed securities 0 0
Total investments 0 0
Cash and cash equivalents 0 0
Certificates of deposit 0 0
U.S. Treasury securities and obligations of U.S. government corporations and agencies 0 0
Total restricted deposits 0 0
Interest rate swap contract 0 0
Total assets at fair value $ 0 $ 0