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, 2011
Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 653,788 $ 629,758
Gross Unrealized Gains 10,510 11,015
Gross Unrealized Losses (841) (790)
Fair Value 663,457 639,983
U.S. Treasury Securities And Obligations Of U.S. Government Corporations And Agencies [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 29,014 28,665
Gross Unrealized Gains 638 510
Gross Unrealized Losses (13) (140)
Fair Value 29,639 29,035
Corporate Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 186,018 197,577
Gross Unrealized Gains 3,762 3,124
Gross Unrealized Losses (751) (586)
Fair Value 189,029 200,115
Restricted Certificates Of Deposit [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 5,890 6,814
Gross Unrealized Gains      
Gross Unrealized Losses      
Fair Value 5,890 6,814
Restricted Cash Equivalents [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 13,775 8,814
Gross Unrealized Gains      
Gross Unrealized Losses      
Fair Value 13,775 8,814
Municipal Securities, General Obligation [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 126,806 109,866
Gross Unrealized Gains 2,828 3,601
Gross Unrealized Losses (26) (6)
Fair Value 129,608 113,461
Municipal Securities, Pre-Refunded [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 33,247 32,442
Gross Unrealized Gains 465 756
Gross Unrealized Losses      
Fair Value 33,712 33,198
Municipal Securities, Revenue [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 118,507 100,198
Gross Unrealized Gains 2,387 2,781
Gross Unrealized Losses (34) (15)
Fair Value 120,860 102,964
Municipal Securities, Variable Rate Demand Notes [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 64,658 106,540
Gross Unrealized Gains      
Gross Unrealized Losses      
Fair Value 64,658 106,540
Asset Backed Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 51,779 17,391
Gross Unrealized Gains 430 243
Gross Unrealized Losses (17) (43)
Fair Value 52,192 17,591
Cost And Equity Method Investments [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 9,395 7,060
Gross Unrealized Gains      
Gross Unrealized Losses      
Fair Value 9,395 7,060
Life Insurance Contracts [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 14,699 14,391
Gross Unrealized Gains      
Gross Unrealized Losses      
Fair Value $ 14,699 $ 14,391