| Assets And Liabilities Measured At Fair Value On A Recurring Basis | 
 Assets and liabilities measured at fair value on a recurring basis as of September 30, 2020 were as follows: 
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| (in thousands) | 
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Level 1 | 
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Level 2 | 
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Level 3 | 
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Total | 
 
| Assets: | 
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| Cash equivalents: | 
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| Money market funds | 
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$ | 
56,337  | 
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$ | 
—  | 
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$ | 
—  | 
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$ | 
56,337  | 
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| Other short-term investments: | 
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| Money market funds | 
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70  | 
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—  | 
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—  | 
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 | 
70  | 
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| Mutual fund shares | 
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1,025  | 
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—  | 
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—  | 
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 | 
1,025  | 
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| Other current assets: | 
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| Derivative financial instruments | 
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—  | 
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6,940  | 
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—  | 
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 | 
6,940  | 
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| Other non-current assets: | 
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| Money market funds | 
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4,621  | 
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—  | 
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—  | 
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4,621  | 
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| Mutual fund shares | 
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11,974  | 
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—  | 
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—  | 
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11,974  | 
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| Derivative financial instruments | 
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—  | 
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 | 
3,454  | 
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—  | 
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 | 
3,454  | 
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| Total assets measured at fair value | 
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$ | 
74,027  | 
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$ | 
10,394  | 
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$ | 
—  | 
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$ | 
84,421  | 
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| Liabilities: | 
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| Accrued liabilities: | 
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| Derivative financial instruments | 
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$ | 
—  | 
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$ | 
2,415  | 
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$ | 
—  | 
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$ | 
2,415  | 
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| Other long-term liabilities: | 
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| Derivative financial instruments | 
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—  | 
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1,186  | 
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—  | 
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 | 
1,186  | 
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| Total liabilities measured at fair value | 
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$ | 
—  | 
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$ | 
3,601  | 
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$ | 
—  | 
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$ | 
3,601  | 
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Assets and liabilities measured at fair value on a recurring basis as of December 31, 2019 were as follows: 
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| (in thousands) | 
 | 
Level 1 | 
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Level 2 | 
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Level 3 | 
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Total | 
 
| Assets: | 
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| Cash equivalents: | 
 | 
 | 
 | 
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 | 
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| Money market funds | 
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$ | 
288,926  | 
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 | 
$ | 
—  | 
 | 
 | 
$ | 
—  | 
 | 
 | 
$ | 
288,926  | 
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| United States government treasury bills | 
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—  | 
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 | 
34,928  | 
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—  | 
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 | 
34,928  | 
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| Commercial paper | 
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—  | 
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 | 
33,587  | 
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—  | 
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33,587  | 
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| Other short-term investments: | 
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| Mutual fund shares | 
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1,668  | 
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—  | 
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—  | 
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 | 
1,668  | 
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| Other current assets: | 
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| Derivative financial instruments | 
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—  | 
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14,001  | 
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—  | 
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 | 
14,001  | 
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| Other non-current assets: | 
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| Money market funds | 
 | 
1,792  | 
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—  | 
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—  | 
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 | 
1,792  | 
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| Mutual fund shares | 
 | 
12,172  | 
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—  | 
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—  | 
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 | 
12,172  | 
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| Derivative financial instruments | 
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—  | 
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 | 
4,159  | 
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—  | 
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 | 
4,159  | 
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| Total assets measured at fair value | 
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$ | 
304,558  | 
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$ | 
86,675  | 
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$ | 
—  | 
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$ | 
391,233  | 
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| Liabilities: | 
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| Accrued liabilities: | 
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| Derivative financial instruments | 
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$ | 
—  | 
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$ | 
2,266  | 
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$ | 
—  | 
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$ | 
2,266  | 
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| Other long-term liabilities: | 
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 | 
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| Derivative financial instruments | 
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—  | 
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 | 
768  | 
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—  | 
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 | 
768  | 
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| Total liabilities measured at fair value | 
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$ | 
—  | 
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$ | 
3,034  | 
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$ | 
—  | 
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$ | 
3,034  | 
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Assets and liabilities measured at fair value on a recurring basis as of September 30, 2019 were as follows: 
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| (in thousands) | 
 | 
Level 1 | 
 | 
Level 2 | 
 | 
Level 3 | 
 | 
Total | 
 
| Assets: | 
 | 
 | 
 | 
 | 
 | 
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 | 
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| Cash equivalents: | 
 | 
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 | 
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| Money market funds | 
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$ | 
72,941  | 
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 | 
$ | 
—  | 
 | 
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$ | 
—  | 
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$ | 
72,941  | 
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| Other short-term investments: | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
| Mutual funds shares | 
 | 
1,477  | 
 | 
 | 
—  | 
 | 
 | 
—  | 
 | 
 | 
1,477  | 
 | 
 
| Other current assets: | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
| Derivative financial instruments | 
 | 
—  | 
 | 
 | 
18,460  | 
 | 
 | 
—  | 
 | 
 | 
18,460  | 
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| Other non-current assets: | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
| Money market funds | 
 | 
1,528  | 
 | 
 | 
—  | 
 | 
 | 
—  | 
 | 
 | 
1,528  | 
 | 
 
| Mutual fund shares  | 
 | 
11,362  | 
 | 
 | 
—  | 
 | 
 | 
—  | 
 | 
 | 
11,362  | 
 | 
 
| Derivative financial instruments | 
 | 
—  | 
 | 
 | 
4,830  | 
 | 
 | 
—  | 
 | 
 | 
4,830  | 
 | 
 
| Total assets measured at fair value | 
 | 
$ | 
87,308  | 
 | 
 | 
$ | 
23,290  | 
 | 
 | 
$ | 
—  | 
 | 
 | 
$ | 
110,598  | 
 | 
 
| Liabilities: | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
| Accrued liabilities: | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
| Derivative financial instruments | 
 | 
$ | 
—  | 
 | 
 | 
$ | 
521  | 
 | 
 | 
$ | 
—  | 
 | 
 | 
$ | 
521  | 
 | 
 
| Other long-term liabilities: | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
| Derivative financial instruments | 
 | 
—  | 
 | 
 | 
109  | 
 | 
 | 
—  | 
 | 
 | 
109  | 
 | 
 
| Total liabilities measured at fair value | 
 | 
$ | 
—  | 
 | 
 | 
$ | 
630  | 
 | 
 | 
$ | 
—  | 
 | 
 | 
$ | 
630  | 
 | 
 
  
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