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
Jun. 30, 2020
Dec. 31, 2019
Jun. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value $ 190,651 $ 391,233 $ 300,910
Total liabilities measured at fair value 604 3,034 2,230
Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 168,396 304,558 143,840
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 22,255 86,675 157,070
Total liabilities measured at fair value 604 3,034 2,230
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 604 2,266 2,090
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 604 2,266 2,090
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   768 140
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   768 140
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 151,823    
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 151,823    
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    
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    
Cash Equivalents [Member] | US Treasury Securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   34,928  
Cash Equivalents [Member] | US Treasury Securities [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] | US Treasury Securities [Member] | Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   34,928  
Cash Equivalents [Member] | US Treasury 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  
Cash Equivalents [Member] | Commercial Paper [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   33,587  
Cash Equivalents [Member] | Commercial Paper [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] | Commercial Paper [Member] | Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   33,587  
Cash Equivalents [Member] | Commercial Paper [Member] | Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value   0  
Available-For-Sale Short-Term Investments [Member] | Repurchase Agreements [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value     136,721
Available-For-Sale Short-Term Investments [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
Available-For-Sale Short-Term Investments [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     136,721
Available-For-Sale Short-Term Investments [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
Cash and 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   288,926 130,097
Cash and 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   288,926 130,097
Cash and 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
Cash and 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
Short-term Investments [Member] | Money Market Funds [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 51    
Short-term Investments [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 51    
Short-term Investments [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    
Short-term Investments [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    
Short-term Investments [Member] | Mutual Fund [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 924 1,668 1,477
Short-term Investments [Member] | Mutual Fund [Member] | Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 924 1,668 1,477
Short-term Investments [Member] | Mutual Fund [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
Short-term Investments [Member] | Mutual Fund [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 15,480 14,001 13,573
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 15,480 14,001 13,573
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
Other Noncurrent Assets [Member] | Money Market Funds [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 4,173 1,792 1,312
Other Noncurrent Assets [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 4,173 1,792 1,312
Other Noncurrent Assets [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
Other Noncurrent Assets [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
Other Noncurrent Assets [Member] | Mutual Fund [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 11,425 12,172 10,954
Other Noncurrent Assets [Member] | Mutual Fund [Member] | Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Total assets measured at fair value 11,425 12,172 10,954
Other Noncurrent Assets [Member] | Mutual Fund [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
Other Noncurrent Assets [Member] | Mutual Fund [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 Noncurrent 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 6,775 4,159 6,776
Other Noncurrent 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 Noncurrent 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 6,775 4,159 6,776
Other Noncurrent 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