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Investments - Additional Information (Detail) | 12 Months Ended
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Sep. 27, 2019 USD ($) investment | Sep. 28, 2018 USD ($) | Sep. 29, 2017 USD ($)
Debt Securities, Available-for-sale [Line Items] |  |  |
Proceeds from sales and maturities of short-term investments | $ 173,020,000 | $ 100,375,000 | $ 44,555,000
Gross realized gains | 200,000 |  |
Gross realized losses on available-for-sale securities | $ 200,000 | 300,000 |
Number of equity investments | investment | 2 |  |
Loss on minority equity investment | $ 7,481,000 | 10,406,000 | $ 0
Preferred Stock | Privately Held Manufacturing Company |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Investments | 5,000,000.0 |  |
Impairment on investments | $ 0 |  |
Equity Securities |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Minority investment (as a percent) | 20.00% |  |
Equity Securities | Compute |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Investments | $ 36,500,000 |  |
Minority investment (as a percent) | 20.00% |  |
Initial value | $ 36,500,000 |  |
Loss on minority equity investment | 7,500,000 | 10,400,000 |
Carrying value | $ 18,600,000 | 26,100,000 |
Maximum |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross realized gains |  | $ 100,000 |

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