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Investments & Fair Value Measurements (Schedule Of Financial Assets and Liabilities Carried At Fair Value) (Details) - USD ($) $ in Thousands	6 Months Ended
	Apr. 01, 2016	Sep. 25, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Document Period End Date	Apr. 01, 2016
Cash and Cash Equivalents, Fair Value Disclosure	$ 521,202	$ 531,926
Available-for-sale Debt Securities, Amortized Cost Basis	394,280	476,407
Available-for-sale Securities, Debt Securities	395,041	476,419
Available-for-sale Securities	268,091	321,015
Investment Owned, at Cost	892,289	991,104
Investment Owned, Unrecognized Unrealized Appreciation	1,579	1,218
Investment Owned, Unrecognized Unrealized Depreciation	(308)	(480)
Cash Cash Equivalents And Investments Total	893,560	991,842
Financial assets carried at fair value		531,926
Contingent Consideration Classified as Equity, Fair Value Disclosure	95	95
Restricted Cash and Cash Equivalents	5,278	2,936
Long-term investments	268,091	321,015
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	119,640	202,515
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(308)	(480)
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis	130,547	158,957
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value	130,505	159,090
Available For Sale Securities Debt Maturities After One Through Two Years Amortized Cost	125,706	173,571
Available For Sale Securities Debt Maturities After One Through Two Years Fair Value	125,932	173,577
Available For Sale Securities Debt Maturities After Two Through Three Years Amortized Cost	138,027	143,879
Available For Sale Securities Debt Maturities After Two Through Three Years Fair Value	138,604	143,752
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	26,238	19,014
Investments, Fair Value Disclosure		2,001
Investments, Noncurrent, Fair Value Disclosure	26,730	33,233
Financial assets carried at fair value	52,968	54,248
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		1,176
Investments, Fair Value Disclosure	104,267	136,900
Investments, Noncurrent, Fair Value Disclosure	238,315	284,821
Financial assets carried at fair value	342,582	422,897
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent Consideration Classified as Equity, Fair Value Disclosure	95	95
Cash [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	494,964	511,736
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	26,238	19,014
Money Market Funds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	26,238	19,014
Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	13,000
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(15)
Available-for-sale Securities	12,985
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	12,986	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(15)	0
Certificates of Deposit [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	12,985
U.S. Agency Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		2,000
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax		1
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax		0
Available-for-sale Securities, Debt Securities		2,001
Available-for-sale Securities, Amortized Cost Basis	11,631	1,999
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	39	1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(1)	0
Available-for-sale Securities	11,669	2,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	2,996	19,005
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2)	(17)
U.S. Agency Securities [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure		2,001
Investments, Noncurrent, Fair Value Disclosure	11,669	2,000
Government Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	14,483	30,505
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	70	19
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(1)	(17)
Available-for-sale Securities	14,552	30,507
Government Bonds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	14,552	30,507
Commercial Paper [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	13,867	6,478
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	22	0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(7)	0
Available-for-sale Securities, Debt Securities	13,882	6,478
Investment Owned, at Cost	13,860	0
Investment Owned, Unrecognized Unrealized Appreciation	7	0
Commercial Paper [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	13,882	6,478
Corporate Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		1,176
Available-for-sale Debt Securities, Amortized Cost Basis	71,851	86,543
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	0	46
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(51)	(11)
Available-for-sale Securities, Debt Securities	71,800	86,578
Available-for-sale Securities, Amortized Cost Basis	189,585	167,394
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	810	138
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(197)	(392)
Available-for-sale Securities	190,198	167,140
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	71,460	148,034
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(248)	(403)
Corporate Bonds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure		1,176
Corporate Bonds [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	71,800	86,578
Investments, Noncurrent, Fair Value Disclosure	190,198	167,140
Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	18,591	43,746
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	8	98
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(14)	0
Available-for-sale Securities, Debt Securities	18,585	43,844
Available-for-sale Securities, Amortized Cost Basis	35,033	117,552
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	121	189
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(22)	(60)
Available-for-sale Securities	35,132	117,681
Investment Owned, at Cost	18,338	35,476
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(36)	(60)
Municipal Bonds [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	18,585	43,844
Investments, Noncurrent, Fair Value Disclosure	35,132	117,681
Short-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	104,309	138,767
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	30	145
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(72)	(11)
Available-for-sale Securities, Debt Securities	104,267	138,901
Other Long-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	3,046	2,961
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	509	726
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available-for-sale Securities	3,555	3,687
Investments, Noncurrent, Fair Value Disclosure	600	500
Cost Method Investment, Fair Value Measurement Adjustment	500	700
Other Long-term Investments [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	509	726
Long-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	266,778	320,411
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,549	1,073
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(236)	(469)
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	2,404	2,498
Financial liabilities carried at fair value	2,404	2,498
Cost Method Investment 1 [Member] | Other Long-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments	2,000	2,000
Cost Method Investment 2 [Member] | Other Long-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments	$ 500	$ 500

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Total Cash, Cash Equivalents And Investments

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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