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Investments - Additional Information (Detail)	12 Months Ended
	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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