Annual report pursuant to Section 13 and 15(d)

Short-Term And Long-Term Investments And Restricted Deposits (Short-Term And Long-Term Investments And Restricted Deposits By Investment Type) (Details)

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Short-Term And Long-Term Investments And Restricted Deposits (Short-Term And Long-Term Investments And Restricted Deposits By Investment Type) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost $ 779,645 $ 653,788
Gross Unrealized Gains 9,481 10,510
Gross Unrealized Losses (492) (841)
Fair Value 788,634 663,457
U.S. Treasury Securities And Obligations Of U.S. Government Corporations And Agencies [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 117,434 29,014
Gross Unrealized Gains 594 638
Gross Unrealized Losses (221) (13)
Fair Value 117,807 29,639
Corporate Securities [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 315,807 186,018
Gross Unrealized Gains 5,101 3,762
Gross Unrealized Losses (198) (751)
Fair Value 320,710 189,029
Restricted Certificates Of Deposit [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 5,890 5,890
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 5,890 5,890
Restricted Cash Equivalents [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 14,460 13,775
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 14,460 13,775
Municipal Securities, General Obligation [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 88,690 126,806
Gross Unrealized Gains 1,173 2,828
Gross Unrealized Losses (26) (26)
Fair Value 89,837 129,608
Municipal Securities, Pre-Refunded [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 5,337 33,247
Gross Unrealized Gains 85 465
Gross Unrealized Losses 0 0
Fair Value 5,422 33,712
Municipal Securities, Revenue [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 84,726 118,507
Gross Unrealized Gains 1,331 2,387
Gross Unrealized Losses (30) (34)
Fair Value 86,027 120,860
Municipal Securities, Variable Rate Demand Notes [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 37,685 64,658
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 37,685 64,658
Asset Backed Securities [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 83,295 51,779
Gross Unrealized Gains 1,197 430
Gross Unrealized Losses (17) (17)
Fair Value 84,475 52,192
Cost And Equity Method Investments [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 11,298 9,395
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 11,298 9,395
Life Insurance Contracts [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 15,023 14,699
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value $ 15,023 $ 14,699