| Assets And Liabilities Measured At Fair Value On A Recurring Basis | 
 
Assets and liabilities measured at fair value on a recurring basis as of June 30, 2019 were as follows:
 
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(in thousands)  | 
   | 
Level 1  | 
   | 
Level 2  | 
   | 
Level 3  | 
   | 
Total  | 
 
Assets:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Cash equivalents:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Money market funds  | 
   | 
$  | 
130,097  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
130,097  | 
 
  | 
 
Available-for-sale short-term investments (1):
  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
U.S. Government treasury bills  | 
   | 
—  | 
 
  | 
   | 
136,721  | 
 
  | 
   | 
—  | 
 
  | 
   | 
136,721  | 
 
  | 
 
Other short-term investments:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Mutual fund shares  | 
   | 
1,477  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
1,477  | 
 
  | 
 
Other current assets:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Derivative financial instruments (Note 15)  | 
   | 
—  | 
 
  | 
   | 
13,573  | 
 
  | 
   | 
—  | 
 
  | 
   | 
13,573  | 
 
  | 
 
Other non-current assets:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Money market funds  | 
   | 
1,312  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
1,312  | 
 
  | 
 
Mutual fund shares  | 
   | 
10,954  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
10,954  | 
 
  | 
 
Derivative financial instruments (Note 15)  | 
   | 
—  | 
 
  | 
   | 
6,776  | 
 
  | 
   | 
—  | 
 
  | 
   | 
6,776  | 
 
  | 
 
Total assets measured at fair value  | 
   | 
$  | 
143,840  | 
 
  | 
   | 
$  | 
157,070  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
300,910  | 
 
  | 
 
Liabilities:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Accrued liabilities:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Derivative financial instruments (Note 15)  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
2,090  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
2,090  | 
 
  | 
 
Other long-term liabilities:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Derivative financial instruments (Note 15)  | 
   | 
—  | 
 
  | 
   | 
140  | 
 
  | 
   | 
—  | 
 
  | 
   | 
140  | 
 
  | 
 
Total liabilities measured at fair value  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
2,230  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
2,230  | 
 
  | 
 
  
(1)     Investments have remaining maturities of less than one year.
 
Assets and liabilities measured at fair value on a recurring basis as of December 31, 2018 were as follows:
 
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 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
(in thousands)  | 
   | 
Level 1  | 
   | 
Level 2  | 
   | 
Level 3  | 
   | 
Total  | 
 
Assets:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Cash equivalents:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Money market funds  | 
   | 
$  | 
122,237  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
122,237  | 
 
  | 
 
U.S. Government treasury bills  | 
   | 
—  | 
 
  | 
   | 
39,952  | 
 
  | 
   | 
—  | 
 
  | 
   | 
39,952  | 
 
  | 
 
Available-for-sale short-term investments (1)
  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
U.S. Government treasury bills  | 
   | 
—  | 
 
  | 
   | 
261,602  | 
 
  | 
   | 
—  | 
 
  | 
   | 
261,602  | 
 
  | 
 
Other short-term investments:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Mutual fund shares  | 
   | 
1,200  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
1,200  | 
 
  | 
 
Other current assets:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Derivative financial instruments (Note 15)  | 
   | 
—  | 
 
  | 
   | 
13,615  | 
 
  | 
   | 
—  | 
 
  | 
   | 
13,615  | 
 
  | 
 
Other non-current assets:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Money market funds  | 
   | 
869  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
869  | 
 
  | 
 
Mutual fund shares  | 
   | 
8,606  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
8,606  | 
 
  | 
 
Derivative financial instruments (Note 15)  | 
   | 
—  | 
 
  | 
   | 
9,922  | 
 
  | 
   | 
—  | 
 
  | 
   | 
9,922  | 
 
  | 
 
Total assets measured at fair value  | 
   | 
$  | 
132,912  | 
 
  | 
   | 
$  | 
325,091  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
458,003  | 
 
  | 
 
Liabilities:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Accrued liabilities:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Derivative financial instruments (Note 15)  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
1,017  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
1,017  | 
 
  | 
 
Other long-term liabilities:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Derivative financial instruments (Note 15)  | 
   | 
—  | 
 
  | 
   | 
1  | 
 
  | 
   | 
—  | 
 
  | 
   | 
1  | 
 
  | 
 
Total liabilities measured at fair value  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
1,018  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
1,018  | 
 
  | 
 
  
(1)     Investments have remaining maturities of less than one year.
 
Assets and liabilities measured at fair value on a recurring basis as of June 30, 2018 were as follows:
 
 |  
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 | 
 
(in thousands)  | 
   | 
Level 1  | 
   | 
Level 2  | 
   | 
Level 3  | 
   | 
Total  | 
 
Assets:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Cash equivalents:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Money market funds  | 
   | 
$  | 
144,729  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
144,729  | 
 
  | 
 
Time deposits  | 
   | 
61,563  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
61,563  | 
 
  | 
 
U.S. Government treasury bills  | 
   | 
—  | 
 
  | 
   | 
121,352  | 
 
  | 
   | 
—  | 
 
  | 
   | 
121,352  | 
 
  | 
 
Available-for-sale short-term investments (1):
  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
U.S. Government treasury bills  | 
   | 
—  | 
 
  | 
   | 
225,247  | 
 
  | 
   | 
—  | 
 
  | 
   | 
225,247  | 
 
  | 
 
U.S. Government-backed municipal bonds  | 
   | 
—  | 
 
  | 
   | 
37,335  | 
 
  | 
   | 
—  | 
 
  | 
   | 
37,335  | 
 
  | 
 
Other short-term investments:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Mutual funds shares  | 
   | 
1,432  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
1,432  | 
 
  | 
 
Other current assets:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Derivative financial instruments (Note 15)  | 
   | 
—  | 
 
  | 
   | 
7,163  | 
 
  | 
   | 
—  | 
 
  | 
   | 
7,163  | 
 
  | 
 
Other non-current assets:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Mutual fund shares   | 
   | 
9,332  | 
 
  | 
   | 
—  | 
 
  | 
   | 
—  | 
 
  | 
   | 
9,332  | 
 
  | 
 
Derivative financial instruments (Note 15)  | 
   | 
—  | 
 
  | 
   | 
10,516  | 
 
  | 
   | 
—  | 
 
  | 
   | 
10,516  | 
 
  | 
 
Total assets measured at fair value  | 
   | 
$  | 
217,056  | 
 
  | 
   | 
$  | 
401,613  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
618,669  | 
 
  | 
 
Liabilities:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Accrued liabilities:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Derivative financial instruments (Note 15)  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
2,895  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
2,895  | 
 
  | 
 
Other long-term liabilities:  | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
   | 
 
Derivative financial instruments (Note 15)  | 
   | 
—  | 
 
  | 
   | 
327  | 
 
  | 
   | 
—  | 
 
  | 
   | 
327  | 
 
  | 
 
Total liabilities measured at fair value  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
3,222  | 
 
  | 
   | 
$  | 
—  | 
 
  | 
   | 
$  | 
3,222  | 
 
  | 
 
  
 
 
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