Fair values were as follows: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | June 29, 2019 | | June 30, 2018 | | Amortized Cost | | Gross Unrealized Gain | | Gross Unrealized Loss | | Estimated Fair Value | | Amortized Cost | | Gross Unrealized Gain | | Gross Unrealized Loss | | Estimated Fair Value | | (in thousands) | Available-for-sale investments | | | | | | | | | | | | | | | Certificates of deposit | $ | 1,000 |
| | $ | — |
| | $ | — |
| | $ | 1,000 |
| | $ | 52,429 |
| | $ | — |
| | $ | (1 | ) | | $ | 52,428 |
| Commercial paper | — |
| | — |
| | — |
| | — |
| | 64,354 |
| | — |
| | — |
| | 64,354 |
| Corporate debt securities | 140,031 |
| | 68 |
| | (109 | ) | | 139,990 |
| | 369,734 |
| | 39 |
| | (2,008 | ) | | 367,765 |
| U.S. Treasury securities | — |
| | — |
| | — |
| | — |
| | 600,068 |
| | 10 |
| | (1,710 | ) | | 598,368 |
| Total available-for-sale investments | $ | 141,031 |
| | $ | 68 |
| | $ | (109 | ) | | $ | 140,990 |
| | $ | 1,086,585 |
| | $ | 49 |
| | $ | (3,719 | ) | | $ | 1,082,915 |
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