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 |