Investments & Fair Value Measurements (Schedule Of Financial Assets and Liabilities Carried At Fair Value) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Mar. 26, 2021	Sep. 25, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash Equivalents, at Carrying Value	$ 1,104,570
Cash and Cash Equivalents, Fair Value Disclosure		$ 1,071,876
Cash and cash equivalents	1,104,570	1,071,876
Debt Securities, Available-for-sale, Unrealized Loss	0	0
Debt Securities, Available-for-sale, Amortized Cost	409,543	309,067
Debt Securities, Available-for-sale	410,117	310,058
Debt Securities, Available-for-sale, Unrealized Gain	0
Investment Owned, Unrecognized Unrealized Depreciation	(23)	(16)
Cash Cash Equivalents And Investments Total	1,205,340	1,170,973
Financial assets carried at fair value	1,104,570	1,071,876
Restricted Cash and Cash Equivalents	8,926	8,103
Long-term investments	42,188	52,149
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	25,122	9,581
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(22)	(16)
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	371,358	261,839
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value	371,608	262,085
Available For Sale Securities Debt Maturities After One Through Two Years Amortized Cost	23,164	29,328
Available For Sale Securities Debt Maturities After One Through Two Years Fair Value	23,459	29,814
Available For Sale Securities Debt Maturities After Two Through Three Years Amortized Cost	15,021	17,900
Available For Sale Securities Debt Maturities After Two Through Three Years Fair Value	15,050	18,159
Investment Owned, at Cost	1,204,766	1,169,983
Investment Owned, Unrecognized Unrealized Appreciation	597	1,006
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	1,104,570	1,070,976
Financial assets carried at fair value	1,106,297	1,073,979
Derivative Asset		0
Derivative Liability		0
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	900
Financial assets carried at fair value	95,365	92,818
Derivative Asset		4,267
Derivative Liability		(79)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset		0
Derivative Liability		0
Cash [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash Equivalents, at Carrying Value	791,545
Cash and Cash Equivalents, Fair Value Disclosure	791,545	856,740
Cash [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	791,545	856,740
Commercial Paper [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		900
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash Equivalents, at Carrying Value	312,685
Cash and Cash Equivalents, Fair Value Disclosure	312,685	214,111
Money Market Funds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	312,685	214,111
Government Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash Equivalents, at Carrying Value	340
Cash and Cash Equivalents, Fair Value Disclosure	340
Debt Securities, Available-for-sale, Unrealized Loss	0
Debt Securities, Available-for-sale, Unrealized Gain	0
Government Bonds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	340
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		214,111
Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	630	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
U.S. Agency Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	555	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1)	0
U.S. Agency Securities [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure		0
US Government Agencies Short-term Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss	0
Debt Securities, Available-for-sale	1,417	1,011
Debt Securities, Available-for-sale, Unrealized Gain	20
US Government Agencies Short-term Debt Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	1,417
Government Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		125
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	3,929	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(6)	0
Government Bonds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		125
Government Bonds [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		0
Commercial Paper [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		900
Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	14,261	7,076
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(13)	(10)
Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2)	(6)
Investment Owned, at Cost	5,747	2,505
Short-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Unrealized Gain		248
Other Long-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	3,700	4,200
Investments Held In Supplemental Retirement Plan [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets carried at fair value	4,545	4,279
Financial liabilities carried at fair value	4,545	4,279
Short-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss		(3)
Debt Securities, Available-for-sale, Amortized Cost		46,703
Debt Securities, Available-for-sale		46,948
Short-term Investments [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	100	1,370
Short-term Investments [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	58,482	45,578
Short-term Investments [Member] | Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss	0	0
Debt Securities, Available-for-sale, Amortized Cost	1,825	2,277
Debt Securities, Available-for-sale	1,825
Debt Securities, Available-for-sale, Unrealized Gain	0	1
Available-for-sale Securities		2,278
Short-term Investments [Member] | Certificates of Deposit [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	1,825	2,278
Short-term Investments [Member] | U.S. Agency Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		999
Short-term Investments [Member] | US Government Agencies Short-term Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss		0
Debt Securities, Available-for-sale, Amortized Cost	1,397
Debt Securities, Available-for-sale, Unrealized Gain		12
Short-term Investments [Member] | US Government Agencies Short-term Debt Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure		1,011
Short-term Investments [Member] | Government Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss	0	0
Debt Securities, Available-for-sale, Amortized Cost	1,645	5,118
Debt Securities, Available-for-sale	1,656	5,165
Debt Securities, Available-for-sale, Unrealized Gain	11	47
Short-term Investments [Member] | Government Bonds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	100	1,370
Short-term Investments [Member] | Government Bonds [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	1,556	3,795
Short-term Investments [Member] | Commercial Paper [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss	0	0
Debt Securities, Available-for-sale, Amortized Cost	6,079	4,727
Debt Securities, Available-for-sale	6,081	4,731
Debt Securities, Available-for-sale, Unrealized Gain	2	4
Short-term Investments [Member] | Commercial Paper [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	6,081	4,731
Short-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss	(3)	(3)
Debt Securities, Available-for-sale, Amortized Cost	24,461	18,754
Debt Securities, Available-for-sale	24,574	18,838
Debt Securities, Available-for-sale, Unrealized Gain	116	87
Short-term Investments [Member] | Corporate Debt Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	24,574	18,838
Short-term Investments [Member] | Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss	(1)	0
Debt Securities, Available-for-sale, Amortized Cost	22,925	14,828
Debt Securities, Available-for-sale	23,029	14,925
Debt Securities, Available-for-sale, Unrealized Gain	105	97
Short-term Investments [Member] | Municipal Bonds [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	23,029	14,925
Short-term Investments [Member] | Short-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss	(4)
Debt Securities, Available-for-sale, Amortized Cost	58,332
Debt Securities, Available-for-sale	58,582
Debt Securities, Available-for-sale, Unrealized Gain	254
Long-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis		51,404
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		758
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(13)
Available-for-sale Securities		52,149
Long-term Investments [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	1,627	1,633
Long-term Investments [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	36,883	46,340
Long-term Investments [Member] | Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss	0
Debt Securities, Available-for-sale, Amortized Cost	630
Debt Securities, Available-for-sale	630
Debt Securities, Available-for-sale, Unrealized Gain	0
Long-term Investments [Member] | Certificates of Deposit [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	630
Long-term Investments [Member] | U.S. Agency Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,961	2,214
Available-for-sale Securities	1,979	2,270
Available-for-sale Securities, Gross Unrealized Gain	19	56
Available-for-sale Securities, Gross Unrealized Loss	(1)	0
Long-term Investments [Member] | U.S. Agency Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	1,979	2,270
Long-term Investments [Member] | Government Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	7,731	5,137
Available-for-sale Securities	7,781	5,217
Available-for-sale Securities, Gross Unrealized Gain	56	80
Available-for-sale Securities, Gross Unrealized Loss	(6)	0
Long-term Investments [Member] | Government Bonds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	1,627	1,633
Long-term Investments [Member] | Government Bonds [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	6,154	3,584
Long-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	19,477	24,657
Available-for-sale Securities	19,652	25,069
Available-for-sale Securities, Gross Unrealized Gain	186	419
Available-for-sale Securities, Gross Unrealized Loss	(11)	(7)
Long-term Investments [Member] | Corporate Debt Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	19,652	25,069
Long-term Investments [Member] | Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	8,387	15,220
Available-for-sale Securities	8,468	15,417
Available-for-sale Securities, Gross Unrealized Gain	82	203
Available-for-sale Securities, Gross Unrealized Loss	(1)	(6)
Long-term Investments [Member] | Municipal Bonds [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	8,468	15,417
Long-term Investments [Member] | Other Long-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	3,678	4,176
Available-for-sale Securities	3,678	4,176
Available-for-sale Securities, Gross Unrealized Gain	0	0
Available-for-sale Securities, Gross Unrealized Loss	0	0
Long-term Investments [Member] | Other Long-term Investments [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	0	0
Long-term Investments [Member] | Long-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	41,864
Available-for-sale Securities	42,188
Available-for-sale Securities, Gross Unrealized Gain	343
Available-for-sale Securities, Gross Unrealized Loss	(19)
Other Current Assets [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0
Other Current Assets [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	4,977
Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0
Other Noncurrent Assets [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset		0
Other Noncurrent Assets [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset		369
Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset		0
Other Accrued Liabilities | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0
Other Accrued Liabilities | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	(112)
Other Accrued Liabilities | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0
Derivative Financial Instruments, Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments, Assets, Amortized Cost Basis		0
Derivative Financial Instruments, Unrealized Gain		4,267
Derivative Financial Instruments, Unrealized Loss		0
Derivative Asset		4,267
Derivative Financial Instruments, Assets [Member] | Other Current Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments, Assets, Amortized Cost Basis	0
Derivative Financial Instruments, Unrealized Gain	4,977
Derivative Financial Instruments, Unrealized Loss	0
Derivative Asset	4,977
Derivative Financial Instruments, Assets [Member] | Other Noncurrent Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments, Assets, Amortized Cost Basis		0
Derivative Financial Instruments, Unrealized Gain		369
Derivative Financial Instruments, Unrealized Loss		0
Derivative Asset		369
Derivative Financial Instruments, Liabilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments, Unrealized Gain		0
Derivative Financial Instruments, Unrealized Loss		(79)
Derivative Financial Instruments, Liabilities, Amortized Cost Basis		0
Derivative Liability		$ (79)
Derivative Financial Instruments, Liabilities [Member] | Other Accrued Liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments, Unrealized Gain	0
Derivative Financial Instruments, Unrealized Loss	(112)
Derivative Financial Instruments, Liabilities, Amortized Cost Basis	0
Derivative Liability	$ (112)