Annual report pursuant to Section 13 and 15(d)

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

v2.4.0.6
Fair Value Measurements (Fair Value Measurements By Level For Assets Measured At Fair Value On A Recurring Basis) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Cash and cash equivalents $ 843,952 $ 573,698
U.S. Treasury securities and obligations of U.S. government corporations and agencies 103,364 22,486
Corporate securities 320,710 189,029
Municipal securities, General obligation 89,837 129,608
Municipal securities, Pre-refunded 5,422 33,712
Municipal securities, Revenue 86,027 120,860
Municipal securities, Variable rate demand notes 37,685 64,658
Asset backed securities 84,475 52,192
Total investments 727,520 612,545
Cash and cash equivalents 14,460 13,775
Certificates of deposit 5,890 5,890
U.S. Treasury securities and obligations of U.S. government corporations and agencies 14,443 7,153
Total restricted deposits 34,793 26,818
Interest rate swap contract 16,304 11,431
Total assets at fair value 1,622,569 1,224,492
Level I [Member]
    
Cash and cash equivalents 843,952 573,698
U.S. Treasury securities and obligations of U.S. government corporations and agencies 57,114 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 57,114 17,091
Cash and cash equivalents 14,460 13,775
Certificates of deposit 5,890 5,890
U.S. Treasury securities and obligations of U.S. government corporations and agencies 14,443 7,153
Total restricted deposits 34,793 26,818
Interest rate swap contract 0 0
Total assets at fair value 935,859 617,607
Level II [Member]
    
Cash and cash equivalents 0 0
U.S. Treasury securities and obligations of U.S. government corporations and agencies 46,250 5,395
Corporate securities 320,710 189,029
Municipal securities, General obligation 89,837 129,608
Municipal securities, Pre-refunded 5,422 33,712
Municipal securities, Revenue 86,027 120,860
Municipal securities, Variable rate demand notes 37,685 64,658
Asset backed securities 84,475 52,192
Total investments 670,406 595,454
Cash and cash equivalents 0 0
Certificates of deposit 0 0
U.S. Treasury securities and obligations of U.S. government corporations and agencies 0 0
Total restricted deposits 0 0
Interest rate swap contract 16,304 11,431
Total assets at fair value 686,710 606,885
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