Fair Value Measures (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020 | Mar. 31, 2020 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Assets, Fair Value Disclosure | $ 420,205 | $ 378,023 | $ 256,206 |
Liabilities, Fair Value Disclosure | 9,038 | 16,431 | 1,209 |
Fair Value, Inputs, Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Assets, Fair Value Disclosure | 364,849 | 139,318 | 142,287 |
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 | 55,356 | 238,705 | 113,919 |
Liabilities, Fair Value Disclosure | 9,038 | 16,431 | 1,209 |
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 | 344,886 | 119,378 | 128,488 |
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 | 99 | 105 | 14 |
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 | 3,667 | 4,059 | 3,674 |
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 | 344,886 | 119,378 | 128,488 |
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 | 99 | 105 | 14 |
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 | 3,667 | 4,059 | 3,674 |
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 | 45,000 | 234,982 | 44,973 |
US Treasury Securities [Member] | Available-for-sale Securities [Member] | Short-term Investments [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Assets, Fair Value Disclosure | | | 35,032 |
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 | 0 | 0 |
US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Available-for-sale Securities [Member] | Short-term Investments [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 | 45,000 | 234,982 | 44,973 |
US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Available-for-sale Securities [Member] | Short-term Investments [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Assets, Fair Value Disclosure | | | 35,032 |
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 | 0 | 0 |
US Treasury Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Available-for-sale Securities [Member] | Short-term Investments [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 | 4,197 | 2,597 | 23,394 |
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 | 6,159 | 1,126 | 10,520 |
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 | 4,197 | 2,597 | 23,394 |
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 | 6,159 | 1,126 | 10,520 |
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 | 6,701 | 9,841 | 1,209 |
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 | 2,337 | 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 | 6,701 | 9,841 | 1,209 |
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 | 2,337 | 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 | 821 | 1,119 | 782 |
Mutual Fund | Other Noncurrent Assets [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Assets, Fair Value Disclosure | 15,376 | 14,657 | 9,329 |
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 | 821 | 1,119 | 782 |
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 | 15,376 | 14,657 | 9,329 |
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 |