Quarterly report pursuant to Section 13 or 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
Sep. 30, 2013
Dec. 31, 2012
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost $ 982,941 $ 779,645
Gross Unrealized Gains 5,321 9,481
Gross Unrealized Losses (7,810) (492)
Fair Value 980,452 788,634
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 247,051 117,434
Gross Unrealized Gains 308 594
Gross Unrealized Losses (6,196) (221)
Fair Value 241,163 117,807
Corporate Securities [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 327,083 315,807
Gross Unrealized Gains 3,115 5,101
Gross Unrealized Losses (650) (198)
Fair Value 329,548 320,710
Restricted Certificates Of Deposit [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 5,891 5,890
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 5,891 5,890
Restricted Cash Equivalents [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 22,608 14,460
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 22,608 14,460
Municipal Securities, General Obligation [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 61,101 88,690
Gross Unrealized Gains 544 1,173
Gross Unrealized Losses (169) (26)
Fair Value 61,476 89,837
Municipal Securities, Pre-Refunded [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 14,329 5,337
Gross Unrealized Gains 164 85
Gross Unrealized Losses (1) 0
Fair Value 14,492 5,422
Municipal Securities, Revenue [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 76,753 84,726
Gross Unrealized Gains 534 1,331
Gross Unrealized Losses (538) (30)
Fair Value 76,749 86,027
Municipal Securities, Variable Rate Demand Notes [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 65,955 37,685
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 65,955 37,685
Asset Backed Securities [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 128,343 83,295
Gross Unrealized Gains 656 1,197
Gross Unrealized Losses (256) (17)
Fair Value 128,743 84,475
Cost And Equity Method Investments [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 18,538 11,298
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 18,538 11,298
Life Insurance Contracts [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 15,289 15,023
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value $ 15,289 $ 15,023