Investments and Fair Value Measurements (Unrealized Loss Position) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 24, 2021	Sep. 25, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash		$ 1,071,876
Short-term investments, cost	$ 330,129	399,933
Debt Securities, Available-for-sale, Unrealized Loss	0	0
Short term investments, total	330,401	400,301
Investment Owned, at Cost	1,326,765	1,169,983
Investment Owned, Unrecognized Unrealized Appreciation	(325)	(1,006)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	40,984	9,581
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	52	16
Long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost		51,404
Debt Securities, Available-for-sale, Unrealized Loss		13
Certificates of Deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	600	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
U.S. agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,449	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	0
Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	22,964	7,076
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	25	10
Municipal debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment Owned, at Cost	7,031	2,505
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9	6
Government bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash		125
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	8,940	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	16	0
Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash		900
Short-term investments | Certificates of Deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	1,795	2,277
Debt Securities, Available-for-sale, Unrealized Loss	0	0
Short term investments, total	1,795	2,278
Short-term investments | U.S. agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost		999
Short-term investments | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	18,850	18,754
Debt Securities, Available-for-sale, Unrealized Loss	0	3
Short term investments, total	18,966	18,838
Short-term investments | Municipal debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	11,660	14,828
Debt Securities, Available-for-sale, Unrealized Loss	1	0
Short term investments, total	11,688	14,925
Short-term investments | Government bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	100	5,118
Debt Securities, Available-for-sale, Unrealized Loss	0	0
Short term investments, total	102	5,165
Short-term investments | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	5,184	4,727
Debt Securities, Available-for-sale, Unrealized Loss	0	0
Short term investments, total	5,186	4,731
Long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short term investments, total		52,149
Long-term investments | Long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	62,700
Debt Securities, Available-for-sale, Unrealized Loss	51
Short term investments, total	62,819
Long-term investments | U.S. agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	2,264	2,214
Debt Securities, Available-for-sale, Unrealized Loss	2	0
Short term investments, total	2,275	2,270
Long-term investments | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	32,116	24,657
Debt Securities, Available-for-sale, Unrealized Loss	25	7
Short term investments, total	32,152	25,069
Long-term investments | Municipal debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	10,080	15,220
Debt Securities, Available-for-sale, Unrealized Loss	8	6
Short term investments, total	10,130	15,417
Long-term investments | Government bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	11,784	5,137
Debt Securities, Available-for-sale, Unrealized Loss	16	0
Short term investments, total	$ 11,806	$ 5,217