Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measures (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details)

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Fair Value Measures (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $)
In Thousands, unless otherwise specified
 6 Months Ended
Jun. 30, 2013
Dec. 31, 2012
Jun. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value $ 367,772 $ 184,139 $ 173,513
Total liabilities measured at fair value 722 1,322 1,900
Investments, remaining maturity, minimum 3 months    
Investments, remaining maturity, maximum 2 years    
Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 216,156 99,972 98,951
Total liabilities measured at fair value 0   0
Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 151,616 84,167 74,562
Total liabilities measured at fair value 722 1,322 1,900
Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0   0
Total liabilities measured at fair value 0   0
Money Market Funds [Member] | Cash Equivalents [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 186,245 70,857 85,373
Money Market Funds [Member] | Cash Equivalents [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 186,245 70,857 85,373
Money Market Funds [Member] | Cash Equivalents [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0   0
Money Market Funds [Member] | Cash Equivalents [Member] | Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0   0
Time Deposits [Member] | Cash Equivalents [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 41,710 25,035 10,012
Time Deposits [Member] | Cash Equivalents [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 25,073 25,035 10,012
Time Deposits [Member] | Cash Equivalents [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 16,637    
Time Deposits [Member] | Cash Equivalents [Member] | Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0    
Time Deposits [Member] | Available-For-Sale Short-Term Investments [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value     2,109 [1]
Time Deposits [Member] | Available-For-Sale Short-Term Investments [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value     0 [1]
Time Deposits [Member] | Available-For-Sale Short-Term Investments [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value     2,109 [1]
Time Deposits [Member] | Available-For-Sale Short-Term Investments [Member] | Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value     0 [1]
Variable Rate Demand Obligation [Member] | Available-For-Sale Short-Term Investments [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 56,615 [1] 22,640 [1] 9,870 [1]
Variable Rate Demand Obligation [Member] | Available-For-Sale Short-Term Investments [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 56,615 [1] 22,640 [1] 9,870 [1]
Certificates of Deposit [Member] | Cash Equivalents [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   2,450 3,294
Certificates of Deposit [Member] | Cash Equivalents [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   0 0
Certificates of Deposit [Member] | Cash Equivalents [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   2,450 3,294
Certificates of Deposit [Member] | Cash Equivalents [Member] | Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   0 0
Certificates of Deposit [Member] | Available-For-Sale Short-Term Investments [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 4,905 [1] 7,596 [1] 4,598 [1]
Certificates of Deposit [Member] | Available-For-Sale Short-Term Investments [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 4,905 [1] 7,596 [1] 4,598 [1]
U.S. Government-Backed Municipal Bonds [Member] | Cash Equivalents [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 40,741 5,348 28,456
U.S. Government-Backed Municipal Bonds [Member] | Cash Equivalents [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0    
U.S. Government-Backed Municipal Bonds [Member] | Cash Equivalents [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 40,741 5,348 28,456
U.S. Government-Backed Municipal Bonds [Member] | Cash Equivalents [Member] | Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0    
U.S. Government-Backed Municipal Bonds [Member] | Available-For-Sale Short-Term Investments [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 28,004 [1] 14,425 [1] 18,689 [1]
U.S. Government-Backed Municipal Bonds [Member] | Available-For-Sale Short-Term Investments [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 28,004 [1] 14,425 [1] 18,689 [1]
Repurchase Agreements [Member] | Cash Equivalents [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   25,000  
Repurchase Agreements [Member] | Cash Equivalents [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   0  
Repurchase Agreements [Member] | Cash Equivalents [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   25,000  
Derivative Financial Instruments, Liabilities [Member] | Accrued Liabilities [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total liabilities measured at fair value 722 1,322 1,900
Derivative Financial Instruments, Liabilities [Member] | Accrued Liabilities [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total liabilities measured at fair value 0   0
Derivative Financial Instruments, Liabilities [Member] | Accrued Liabilities [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total liabilities measured at fair value 722 1,322 1,900
Derivative Financial Instruments, Liabilities [Member] | Accrued Liabilities [Member] | Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total liabilities measured at fair value 0   0
Mutual Fund Shares [Member] | Trading Securities [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 657    
Mutual Fund Shares [Member] | Trading Securities [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 657    
Mutual Fund Shares [Member] | Trading Securities [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0    
Mutual Fund Shares [Member] | Trading Securities [Member] | Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0    
Mutual Fund Shares [Member] | Non Current Assets [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 4,181 4,080 3,566
Mutual Fund Shares [Member] | Non Current Assets [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 4,181 4,080 3,566
Mutual Fund Shares [Member] | Non Current Assets [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0   0
Mutual Fund Shares [Member] | Non Current Assets [Member] | Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0   0
Derivative Financial Instruments, Assets [Member] | Other Current Assets [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 4,371 6,219 7,546
Derivative Financial Instruments, Assets [Member] | Other Current Assets [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0   0
Derivative Financial Instruments, Assets [Member] | Other Current Assets [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 4,371 6,219 7,546
Derivative Financial Instruments, Assets [Member] | Other Current Assets [Member] | Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0   0
Derivative Financial Instruments, Assets [Member] | Non Current Assets [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   489  
Derivative Financial Instruments, Assets [Member] | Non Current Assets [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   489  
Non Current Assets [Member] | Derivative Financial Instruments, Assets [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 343    
Non Current Assets [Member] | Derivative Financial Instruments, Assets [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value $ 343    
[1] Investments have remaining maturities greater than three months but less than two years and are available for use in current operations.