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Fair Value Measurements (Schedule Of Fair Value Of Financial Assets Measured On A Recurring Basis) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets $ 409,966 $ 628,265
Money market funds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 24,813 76,050
Commercial paper [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 94,682 167,231
Corporate bonds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 240,072 221,949
U.S. Treasury and government sponsored enterprises [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 44,386 132,991
Municipal bonds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 6,013 30,044
Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 24,813 76,050
Level 1 [Member] | Money market funds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 24,813 76,050
Level 1 [Member] | Commercial paper [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 0 0
Level 1 [Member] | Corporate bonds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 0 0
Level 1 [Member] | U.S. Treasury and government sponsored enterprises [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 0 0
Level 1 [Member] | Municipal bonds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 0 0
Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 385,153 552,215
Level 2 [Member] | Money market funds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 0 0
Level 2 [Member] | Commercial paper [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 94,682 167,231
Level 2 [Member] | Corporate bonds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 240,072 221,949
Level 2 [Member] | U.S. Treasury and government sponsored enterprises [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets 44,386 132,991
Level 2 [Member] | Municipal bonds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fair value of financial assets $ 6,013 $ 30,044