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, 2014
Dec. 31, 2013
Jun. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value $ 262,355 $ 367,420 $ 367,772
Total liabilities measured at fair value 1,743 1,247 722
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 179,400 220,930 216,156
Total liabilities measured at fair value 0 0 0
Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 82,955 146,490 151,616
Total liabilities measured at fair value 1,743 1,247 722
Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 0 0 0
Total liabilities measured at fair value 0 0 0
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 1,731 1,152 722
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 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 1,731 1,152 722
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 0
Other Long Term 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 12 95  
Other Long Term 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  
Other Long Term 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 12 95  
Other Long Term 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  
Cash Equivalents [Member] | Money Market Funds [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 147,953 175,624 186,245
Cash Equivalents [Member] | Money Market Funds [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 147,953 175,624 186,245
Cash Equivalents [Member] | Money Market Funds [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 0
Cash Equivalents [Member] | Money Market Funds [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 0
Cash Equivalents [Member] | Time Deposits [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 39,972 34,637 41,710
Cash Equivalents [Member] | Time Deposits [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 25,148 25,111 25,073
Cash Equivalents [Member] | Time Deposits [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 14,824 9,526 16,637
Cash Equivalents [Member] | Time Deposits [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 0
Cash Equivalents [Member] | Certificates of Deposit [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   735  
Cash Equivalents [Member] | Certificates of Deposit [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   0  
Cash Equivalents [Member] | Certificates of Deposit [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   735  
Cash Equivalents [Member] | Certificates of Deposit [Member] | Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   0  
Cash Equivalents [Member] | Repurchase Agreements [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 40,000 45,000  
Cash Equivalents [Member] | Repurchase Agreements [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  
Cash Equivalents [Member] | Repurchase Agreements [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 40,000 45,000  
Cash Equivalents [Member] | Repurchase Agreements [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  
Cash Equivalents [Member] | U.S. Government-Backed Municipal Bonds [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   9,898 40,741
Cash Equivalents [Member] | U.S. Government-Backed Municipal Bonds [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
Cash Equivalents [Member] | U.S. Government-Backed Municipal Bonds [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   9,898 40,741
Cash Equivalents [Member] | U.S. Government-Backed Municipal Bonds [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
Available-For-Sale Short-Term Investments [Member] | Short-term municipal bond funds [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   15,004 [1]  
Available-For-Sale Short-Term Investments [Member] | Short-term municipal bond funds [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   15,004 [1]  
Available-For-Sale Short-Term Investments [Member] | Short-term municipal bond funds [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   0 [1]  
Available-For-Sale Short-Term Investments [Member] | Short-term municipal bond funds [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]  
Available-For-Sale Short-Term Investments [Member] | Certificates of Deposit [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 3,429 [1] 9,546 [1] 4,905 [1]
Available-For-Sale Short-Term Investments [Member] | Certificates of Deposit [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] 0 [1] 0 [1]
Available-For-Sale Short-Term Investments [Member] | Certificates of Deposit [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 3,429 [1] 9,546 [1] 4,905 [1]
Available-For-Sale Short-Term Investments [Member] | Certificates of Deposit [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] 0 [1] 0 [1]
Available-For-Sale Short-Term Investments [Member] | Variable Rate Demand Obligation [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 18,675 [1] 52,105 [1] 56,615 [1]
Available-For-Sale Short-Term Investments [Member] | Variable Rate Demand Obligation [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] 0 [1]
Available-For-Sale Short-Term Investments [Member] | Variable Rate Demand Obligation [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 18,675 [1] 52,105 [1] 56,615 [1]
Available-For-Sale Short-Term Investments [Member] | Variable Rate Demand Obligation [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] 0 [1]
Available-For-Sale Short-Term Investments [Member] | U.S. Government-Backed Municipal Bonds [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 4,584 [1] 14,764 [1] 28,004 [1]
Available-For-Sale Short-Term Investments [Member] | U.S. Government-Backed Municipal Bonds [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] 0 [1] 0 [1]
Available-For-Sale Short-Term Investments [Member] | U.S. Government-Backed Municipal Bonds [Member] | Level 2 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 4,584 [1] 14,764 [1] 28,004 [1]
Available-For-Sale Short-Term Investments [Member] | U.S. Government-Backed Municipal Bonds [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] 0 [1] 0 [1]
Trading Securities [Member] | Mutual Fund Shares [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 550 336 657
Trading Securities [Member] | Mutual Fund Shares [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 550 336 657
Trading Securities [Member] | Mutual Fund Shares [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 0
Trading Securities [Member] | Mutual Fund Shares [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 0
Other 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 1,288 4,892 4,371
Other Current Assets [Member] | Derivative Financial Instruments, 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 0
Other 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 1,288 4,892 4,371
Other Current Assets [Member] | Derivative Financial Instruments, 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 0
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 155 24 343
Non Current Assets [Member] | Derivative Financial Instruments, 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   
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 155 24 343
Non Current Assets [Member] | Derivative Financial Instruments, 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   
Non Current Assets [Member] | Mutual Fund Shares [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 5,749 4,855 4,181
Non Current Assets [Member] | Mutual Fund Shares [Member] | Level 1 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 5,749 4,855 4,181
Non Current Assets [Member] | Mutual Fund Shares [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 0
Non Current Assets [Member] | Mutual Fund Shares [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 $ 0
[1] (1) Investments have remaining maturities greater than three months but less than two years and are available for use in current opera