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, 2021
Dec. 31, 2020
Jun. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure $ 191,745 $ 378,023 $ 190,651
Liabilities, Fair Value Disclosure 11,577 16,431 604
Fair Value, Inputs, Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 181,545 139,318 168,396
Liabilities, Fair Value Disclosure 0 0 0
Fair Value, Inputs, Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 10,200 238,705 22,255
Liabilities, Fair Value Disclosure 11,577 16,431 604
Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Liabilities, Fair Value Disclosure 0 0 0
Money Market Funds [Member] | Cash Equivalents [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 159,897 119,378 151,823
Money Market Funds [Member] | Short-term Investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 162 105 51
Money Market Funds [Member] | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 3,120 4,059 4,173
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 159,897 119,378 151,823
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 162 105 51
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 3,120 4,059 4,173
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Short-term Investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
US Treasury Securities [Member] | Cash Equivalents [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure   234,982  
US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure   0  
US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure   234,982  
US Treasury Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure   0  
Derivative Financial Instruments, Assets [Member] | Other Current Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 3,428 2,597 15,480
Derivative Financial Instruments, Assets [Member] | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 6,772 1,126 6,775
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 1 [Member] | Other Current Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 1 [Member] | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 2 [Member] | Other Current Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 3,428 2,597 15,480
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 2 [Member] | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 6,772 1,126 6,775
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Other Current Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Derivative Financial Instruments, Liabilities [Member] | Accrued Liabilities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities, Fair Value Disclosure 9,181 9,841 604
Derivative Financial Instruments, Liabilities [Member] | Other Noncurrent Liabilities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities, Fair Value Disclosure 2,396 6,590  
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 1 [Member] | Accrued Liabilities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities, Fair Value Disclosure 0 0 0
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 1 [Member] | Other Noncurrent Liabilities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities, Fair Value Disclosure 0 0  
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 2 [Member] | Accrued Liabilities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities, Fair Value Disclosure 9,181 9,841 604
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 2 [Member] | Other Noncurrent Liabilities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities, Fair Value Disclosure 2,396 6,590  
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member] | Accrued Liabilities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities, Fair Value Disclosure 0 0 0
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member] | Other Noncurrent Liabilities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities, Fair Value Disclosure 0 0  
Mutual Fund | Short-term Investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 976 1,119 924
Mutual Fund | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 17,390 14,657 11,425
Mutual Fund | Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 976 1,119 924
Mutual Fund | Fair Value, Inputs, Level 1 [Member] | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 17,390 14,657 11,425
Mutual Fund | Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Mutual Fund | Fair Value, Inputs, Level 2 [Member] | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Mutual Fund | Fair Value, Inputs, Level 3 [Member] | Short-term Investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 0 0 0
Mutual Fund | Fair Value, Inputs, Level 3 [Member] | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure $ 0 $ 0 $ 0