Short-Term Investments (Details) - USD ($) $ in Thousands	Dec. 29, 2018	Sep. 29, 2018	Dec. 30, 2017
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents, Cost Basis	$ 314,996	$ 310,495
Cash and cash equivalent, Unrealized Gains	1	0
Cash and cash equivalent, Unrealized Losses	0	0
Cash and cash equivalents	314,997	310,495	$ 385,735
Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities: Cost Basis	5,000	120
Available-for-sale securities, Unrealized Gains	19	0
Available-for-sale securities, Unrealized Losses	0	0
Available-for-sale securities: Fair Value	5,019	120
Short-term investments: \| U.S. Treasury and agency obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities: Cost Basis	5,000	120
Available-for-sale securities, Unrealized Gains	19	0
Available-for-sale securities, Unrealized Losses	0	0
Available-for-sale securities: Fair Value	$ 5,019	$ 120

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Cash Equivalent, Unrealized Gains

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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