| Summary of Marketable Securities |
At April 30, 2017, marketable securities consisted of the following (in thousands): | | | | | | | | | | | | | | | | | | Amortized Cost | | Unrealized Gains | | Unrealized Losses | | Aggregate Fair Value | U.S. agency obligations | $ | 1,022,208 |
| | $ | 22 |
| | $ | (1,067 | ) | | $ | 1,021,163 |
| U.S. treasury securities | 254,523 |
| | 2 |
| | (103 | ) | | 254,422 |
| Corporate bonds | 320,798 |
| | 18 |
| | (367 | ) | | 320,449 |
| Commercial paper | 362,364 |
| | — |
| | — |
| | 362,364 |
| Money market funds | 57,308 |
| | — |
| | — |
| | 57,308 |
| | $ | 2,017,201 |
| | $ | 42 |
| | $ | (1,537 | ) | | $ | 2,015,706 |
| Included in cash and cash equivalents | $ | 398,936 |
| | $ | — |
| | $ | — |
| | $ | 398,936 |
| Included in marketable securities | $ | 1,618,265 |
| | $ | 42 |
| | $ | (1,537 | ) | | $ | 1,616,770 |
|
At January 31, 2017, marketable securities consisted of the following (in thousands): | | | | | | | | | | | | | | | | | | Amortized Cost | | Unrealized Gains | | Unrealized Losses | | Aggregate Fair Value | U.S. agency obligations | $ | 908,874 |
| | $ | 179 |
| | $ | (535 | ) | | $ | 908,518 |
| U.S. treasury securities | 192,028 |
| | 48 |
| | (25 | ) | | 192,051 |
| Corporate bonds | 290,272 |
| | 42 |
| | (429 | ) | | 289,885 |
| Commercial paper | 323,106 |
| | — |
| | — |
| | 323,106 |
| Money market funds | 24,425 |
| | — |
| | — |
| | 24,425 |
| | $ | 1,738,705 |
| | $ | 269 |
| | $ | (989 | ) | | $ | 1,737,985 |
| Included in cash and cash equivalents | $ | 281,163 |
| | $ | — |
| | $ | — |
| | $ | 281,163 |
| Included in marketable securities | $ | 1,457,542 |
| | $ | 269 |
| | $ | (989 | ) | | $ | 1,456,822 |
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