| Information about Assets that are Measured at Fair Value on a Recurring Basis |
The following table presents information about our assets and liabilities that are measured at fair value on a recurring basis and their assigned levels within the valuation hierarchy as of April 30, 2017 (in thousands): | | | | | | | | | | | | | | | | | Description | Level 1 | | Level 2 | | Level 3 | | Total | U.S. agency obligations | $ | — |
| | $ | 1,021,163 |
| | $ | — |
| | $ | 1,021,163 |
| U.S. treasury securities | 254,422 |
| | — |
| | — |
| | 254,422 |
| Corporate bonds | — |
| | 320,449 |
| | — |
| | 320,449 |
| Commercial paper | — |
| | 362,364 |
| | — |
| | 362,364 |
| Money market funds | 57,308 |
| | — |
| | — |
| | 57,308 |
| Foreign currency derivative assets | — |
| | 6,934 |
| | — |
| | 6,934 |
| Total assets | $ | 311,730 |
| | $ | 1,710,910 |
| | $ | — |
| | $ | 2,022,640 |
| Foreign currency derivative liabilities | $ | — |
| | $ | 4,229 |
| | $ | — |
| | $ | 4,229 |
| Total liabilities | $ | — |
| | $ | 4,229 |
| | $ | — |
| | $ | 4,229 |
|
The following table presents information about our assets and liabilities that are measured at fair value on a recurring basis and their assigned levels within the valuation hierarchy as of January 31, 2017 (in thousands): | | | | | | | | | | | | | | | | | Description | Level 1 | | Level 2 | | Level 3 | | Total | U.S. agency obligations | $ | — |
| | $ | 908,518 |
| | $ | — |
| | $ | 908,518 |
| U.S. treasury securities | 192,051 |
| | — |
| | — |
| | 192,051 |
| Corporate bonds | — |
| | 289,885 |
| | — |
| | 289,885 |
| Commercial paper | — |
| | 323,106 |
| | — |
| | 323,106 |
| Money market funds | 24,425 |
| | — |
| | — |
| | 24,425 |
| Foreign currency derivative assets | — |
| | 7,909 |
| | — |
| | 7,909 |
| Total assets | $ | 216,476 |
| | $ | 1,529,418 |
| | $ | — |
| | $ | 1,745,894 |
| Foreign currency derivative liabilities | $ | — |
| | $ | 2,127 |
| | $ | — |
| | $ | 2,127 |
| Total liabilities | $ | — |
| | $ | 2,127 |
| | $ | — |
| | $ | 2,127 |
|
|
| Summary of Carrying Amounts and Estimated Fair Values of Financial Instruments |
The following table presents the carrying amounts and estimated fair values of our financial instruments that are not recorded at fair value in the condensed consolidated balance sheets (in thousands): | | | | | | | | | | | | | | | | | | April 30, 2017 | | January 31, 2017 | | Net Carrying Amount Before Unamortized Debt Issuance Costs | | Estimated Fair Value | | Net Carrying Amount Before Unamortized Debt Issuance Costs | | Estimated Fair Value | 0.75% Convertible senior notes | $ | 329,664 |
| | $ | 407,313 |
| | $ | 325,620 |
| | $ | 402,259 |
| 1.50% Convertible senior notes | 215,586 |
| | 311,480 |
| | 213,180 |
| | 310,470 |
|
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