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
Sep. 30, 2021
Dec. 31, 2020
Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure $ 40,606 $ 378,023 $ 84,421
Liabilities, Fair Value Disclosure 2,881 16,431 3,601
Fair Value, Inputs, Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 24,641 139,318 74,027
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 15,965 238,705 10,394
Liabilities, Fair Value Disclosure 2,881 16,431 3,601
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 2,903 119,378 56,337
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 67 105 70
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 3,397 4,059 4,621
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 2,903 119,378 56,337
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 67 105 70
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 3,397 4,059 4,621
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 7,133 2,597 6,940
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 8,832 1,126 3,454
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 7,133 2,597 6,940
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 8,832 1,126 3,454
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 2,415 9,841 2,415
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 466 6,590 1,186
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 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 2,415 9,841 2,415
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 466 6,590 1,186
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 0
Mutual Fund | Short-term Investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 1,065 1,119 1,025
Mutual Fund | Other Noncurrent Assets [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure 17,209 14,657 11,974
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 1,065 1,119 1,025
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 17,209 14,657 11,974
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