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, 2012
Dec. 31, 2011
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost $ 721,699 $ 653,788
Gross Unrealized Gains 11,481 10,510
Gross Unrealized Losses (37) (841)
Fair Value 733,143 663,457
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 60,177 29,014
Gross Unrealized Gains 760 638
Gross Unrealized Losses (6) (13)
Fair Value 60,931 29,639
Corporate Securities [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 257,161 186,018
Gross Unrealized Gains 5,844 3,762
Gross Unrealized Losses (6) (751)
Fair Value 262,999 189,029
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 13,150 13,775
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 13,150 13,775
Municipal Securities, General Obligation [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 91,259 126,806
Gross Unrealized Gains 1,649 2,828
Gross Unrealized Losses 0 (26)
Fair Value 92,908 129,608
Municipal Securities, Pre-Refunded [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 16,529 33,247
Gross Unrealized Gains 130 465
Gross Unrealized Losses 0 0
Fair Value 16,659 33,712
Municipal Securities, Revenue [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 85,281 118,507
Gross Unrealized Gains 1,804 2,387
Gross Unrealized Losses (25) (34)
Fair Value 87,060 120,860
Municipal Securities, Variable Rate Demand Notes [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 92,225 64,658
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 92,225 64,658
Asset Backed Securities [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 74,126 51,779
Gross Unrealized Gains 1,294 430
Gross Unrealized Losses 0 (17)
Fair Value 75,420 52,192
Cost And Equity Method Investments [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 10,958 9,395
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 10,958 9,395
Life Insurance Contracts [Member]
   
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 14,942 14,699
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value $ 14,942 $ 14,699