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
 3 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Mar. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value $ 288,214 $ 184,139 $ 96,736
Total liabilities measured at fair value 803 1,322 488
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 160,361 99,972 73,405
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 127,853 84,167 23,331
Total liabilities measured at fair value 803 1,322 488
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 130,794 70,857 59,853
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 130,794 70,857 59,853
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 26,854 25,035 15,295
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 25,054 25,035 10,000
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 1,800   5,295
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     2,438 [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     2,438 [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 31,500 [1] 22,640 [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 31,500 [1] 22,640 [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  
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  
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  
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  
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 7,599 [1] 7,596 [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 7,599 [1] 7,596 [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   5,348  
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   5,348  
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 31,889 [1] 14,425 [1] 9,590 [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 31,889 [1] 14,425 [1] 9,590 [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 50,000 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 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 50,000 25,000  
Repurchase Agreements [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    
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 4,513 4,080 3,552
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 4,513 4,080 3,552
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 5,065 6,219 5,443
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 5,065 6,219 5,443
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   489 565
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   489 565
Accrued Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total liabilities measured at fair value 803 1,322 488
Accrued Liabilities [Member] | Derivative Financial Instruments, 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
Accrued Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total liabilities measured at fair value 803 1,322 488
Accrued Liabilities [Member] | Derivative Financial Instruments, 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
[1] Investments have remaining maturities greater than three months but less than two years and are available for use in current operations.