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, 2013
Dec. 31, 2012
Cash and Cash Equivalents $ 741,281 $ 843,952
U.S. Treasury securities and obligations of U.S. government corporations and agencies 228,751 103,364
Corporate securities 329,548 320,710
Municipal securities, General obligation 61,476 89,837
Municipal securities, Pre-refunded 14,492 5,422
Municipal securities, Revenue 76,749 86,027
Municipal securities, Variable rate demand notes 65,955 37,685
Asset backed securities 128,743 84,475
Total investments 905,714 727,520
Cash and cash equivalents 22,608 14,460
Certificates of deposit 5,891 5,890
U.S. Treasury securities and obligations of U.S. government corporations and agencies 12,412 14,443
Total restricted deposits 40,911 34,793
Interest rate swap contract 10,596 16,304
Total assets at fair value 1,698,502 1,622,569
Level I [Member]
   
Cash and Cash Equivalents 741,281 843,952
U.S. Treasury securities and obligations of U.S. government corporations and agencies 213,772 57,114
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 213,772 57,114
Cash and cash equivalents 22,608 14,460
Certificates of deposit 5,891 5,890
U.S. Treasury securities and obligations of U.S. government corporations and agencies 12,412 14,443
Total restricted deposits 40,911 34,793
Interest rate swap contract 0 0
Total assets at fair value 995,964 935,859
Level II [Member]
   
Cash and Cash Equivalents 0 0
U.S. Treasury securities and obligations of U.S. government corporations and agencies 14,979 46,250
Corporate securities 329,548 320,710
Municipal securities, General obligation 61,476 89,837
Municipal securities, Pre-refunded 14,492 5,422
Municipal securities, Revenue 76,749 86,027
Municipal securities, Variable rate demand notes 65,955 37,685
Asset backed securities 128,743 84,475
Total investments 691,942 670,406
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 10,596 16,304
Total assets at fair value 702,538 686,710
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