Fair Value Measures (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands | Mar. 31, 2020 | Dec. 31, 2019 | Mar. 31, 2019 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | $ 256,206 | $ 391,233 | $ 433,933 |
Total liabilities measured at fair value | 1,209 | 3,034 | 498 |
Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 142,287 | 304,558 | 137,957 |
Total liabilities measured at fair value | 0 | 0 | 0 |
Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 113,919 | 86,675 | 295,976 |
Total liabilities measured at fair value | 1,209 | 3,034 | 498 |
Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | 0 |
Total liabilities measured at fair value | 0 | 0 | 0 |
Accrued Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total liabilities measured at fair value | 1,209 | 2,266 | 498 |
Accrued Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total liabilities measured at fair value | 0 | 0 | 0 |
Accrued Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total liabilities measured at fair value | 1,209 | 2,266 | 498 |
Accrued Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total liabilities measured at fair value | 0 | 0 | 0 |
Other Long Term Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total liabilities measured at fair value | | 768 | |
Other Long Term Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total liabilities measured at fair value | | 0 | |
Other Long Term Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total liabilities measured at fair value | | 768 | |
Other Long Term Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total liabilities measured at fair value | | 0 | |
Cash Equivalents [Member] | Money Market Funds [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 128,488 | | |
Cash Equivalents [Member] | Money Market Funds [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 128,488 | | |
Cash Equivalents [Member] | Money Market Funds [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | | |
Cash Equivalents [Member] | Money Market Funds [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | | |
Cash Equivalents [Member] | US Treasury Securities [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 44,973 | 34,928 | |
Cash Equivalents [Member] | US Treasury Securities [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | |
Cash Equivalents [Member] | US Treasury Securities [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 44,973 | 34,928 | |
Cash Equivalents [Member] | US Treasury Securities [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | |
Cash Equivalents [Member] | Commercial Paper [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | 33,587 | |
Cash Equivalents [Member] | Commercial Paper [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | 0 | |
Cash Equivalents [Member] | Commercial Paper [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | 33,587 | |
Cash Equivalents [Member] | Commercial Paper [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | 0 | |
Available-For-Sale Short-Term Investments [Member] | Repurchase Agreements [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | | 270,625 |
Available-For-Sale Short-Term Investments [Member] | Repurchase Agreements [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | | 0 |
Available-For-Sale Short-Term Investments [Member] | Repurchase Agreements [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | | 270,625 |
Available-For-Sale Short-Term Investments [Member] | Repurchase Agreements [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | | 0 |
Available-For-Sale Short-Term Investments [Member] | US Treasury Securities [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 35,032 | | |
Available-For-Sale Short-Term Investments [Member] | US Treasury Securities [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | | |
Available-For-Sale Short-Term Investments [Member] | US Treasury Securities [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 35,032 | | |
Available-For-Sale Short-Term Investments [Member] | US Treasury Securities [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | | |
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | 288,926 | 125,073 |
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | 288,926 | 125,073 |
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | 0 | 0 |
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | | 0 | 0 |
Short-term Investments [Member] | Money Market Funds [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 14 | | |
Short-term Investments [Member] | Money Market Funds [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 14 | | |
Short-term Investments [Member] | Money Market Funds [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | | |
Short-term Investments [Member] | Money Market Funds [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | | |
Short-term Investments [Member] | Mutual Fund [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 782 | 1,668 | 1,978 |
Short-term Investments [Member] | Mutual Fund [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 782 | 1,668 | 1,978 |
Short-term Investments [Member] | Mutual Fund [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | 0 |
Short-term Investments [Member] | Mutual Fund [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | 0 |
Other Current Assets [Member] | Derivative Financial Instruments, Assets [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 23,394 | 14,001 | 15,337 |
Other Current Assets [Member] | Derivative Financial Instruments, Assets [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | 0 |
Other Current Assets [Member] | Derivative Financial Instruments, Assets [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 23,394 | 14,001 | 15,337 |
Other Current Assets [Member] | Derivative Financial Instruments, Assets [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | 0 |
Other Noncurrent Assets [Member] | Money Market Funds [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 3,674 | 1,792 | 1,331 |
Other Noncurrent Assets [Member] | Money Market Funds [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 3,674 | 1,792 | 1,331 |
Other Noncurrent Assets [Member] | Money Market Funds [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | 0 |
Other Noncurrent Assets [Member] | Money Market Funds [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | 0 |
Other Noncurrent Assets [Member] | Mutual Fund [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 9,329 | 12,172 | 9,575 |
Other Noncurrent Assets [Member] | Mutual Fund [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 9,329 | 12,172 | 9,575 |
Other Noncurrent Assets [Member] | Mutual Fund [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | 0 |
Other Noncurrent Assets [Member] | Mutual Fund [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | 0 |
Other Noncurrent Assets [Member] | Derivative Financial Instruments, Assets [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 10,520 | 4,159 | 10,014 |
Other Noncurrent Assets [Member] | Derivative Financial Instruments, Assets [Member] | Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 0 | 0 | 0 |
Other Noncurrent Assets [Member] | Derivative Financial Instruments, Assets [Member] | Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | 10,520 | 4,159 | 10,014 |
Other Noncurrent Assets [Member] | Derivative Financial Instruments, Assets [Member] | Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets measured at fair value | $ 0 | $ 0 | $ 0 |