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 |