Investments and Fair Value Measurements (Schedule Of Financial Assets Carried At Fair Value) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 25, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	$ 516,112	$ 531,926
Short-term investments, cost	525,904	476,407
Short term investments, total	526,420	476,419
Long-term investments, total		321,015
Total cash, cash equivalents, and investments, cost	1,030,769	991,104
Total cash, cash equivalents, and investments, unrealized gains	1,251	1,218
Total cash, cash equivalents, and investments, unrealized losses	(375)	(480)
Total cash, cash equivalents, and investments, total	1,031,645	991,842
Assets	516,112	531,926
Other long-term Investments	393,904	321,015
Business Combination, Contingent Consideration, Liability, Fair Value Disclosure		95
US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments, cost	31,971	30,505
Long-term investments, unrealized gains	77	19
Long-term investments, unrealized losses	(12)	(17)
Long-term investments, total	32,036	30,507
U.S. agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost		2,000
Short-term investments, unrealized gains		1
Short-term investments, unrealized losses		0
Short term investments, total		2,001
Long-term investments, cost	27,536	1,999
Long-term investments, unrealized gains	24	1
Long-term investments, unrealized losses	(26)	0
Long-term investments, total	27,534	2,000
Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	1,099
Short-term investments, cost	19,629	6,478
Short-term investments, unrealized gains	1	0
Short-term investments, unrealized losses	(10)	0
Short term investments, total	19,620	6,478
Total cash, cash equivalents, and investments, cost	11,479	0
Total cash, cash equivalents, and investments, unrealized gains	10	0
Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	2,240	1,176
Short-term investments, cost	63,762	86,543
Short-term investments, unrealized gains	24	46
Short-term investments, unrealized losses	(14)	(11)
Short term investments, total	63,772	86,578
Long-term investments, cost	295,921	167,394
Long-term investments, unrealized gains	715	138
Long-term investments, unrealized losses	(266)	(392)
Long-term investments, total	296,370	167,140
Municipal debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	24,334	43,746
Short-term investments, unrealized gains	0	98
Short-term investments, unrealized losses	(15)	0
Short term investments, total	24,319	43,844
Long-term investments, cost	30,090	117,552
Long-term investments, unrealized gains	28	189
Long-term investments, unrealized losses	(32)	(60)
Long-term investments, total	30,086	117,681
Total cash, cash equivalents, and investments, cost	35,625	35,476
Other long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost Method Investment, Fair Value Measurement Adjustment	400	700
Long-term investments, cost	3,002	2,961
Long-term investments, unrealized gains	366	726
Long-term investments, unrealized losses	0	0
Long-term investments, total	3,368	3,687
Long-term investments	500	500
Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	121,637	138,767
Short-term investments, unrealized gains	31	145
Short-term investments, unrealized losses	(39)	(11)
Short term investments, total	121,629	138,901
Long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments, cost	393,020	320,411
Long-term investments, unrealized gains	1,220	1,073
Long-term investments, unrealized losses	(336)	(469)
Long-term investments, total	393,904
Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	13,912
Short-term investments, unrealized gains	6
Short-term investments, unrealized losses	0
Short term investments, total	13,918
Long-term investments, cost	4,500
Long-term investments, unrealized gains	10
Long-term investments, unrealized losses	0
Long-term investments, total	4,510
Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	501,863	511,736
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	10,910	19,014
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	10,910	19,014
Short-term investments	0	2,001
Long-term investments	59,936	33,233
Assets	70,846	54,248
Level 1 | US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments	32,036	30,507
Level 1 | U.S. agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments		2,001
Long-term investments	27,534	2,000
Level 1 | Other long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments	366	726
Level 1 | Investments held in supplemental retirement plan:
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	2,638	2,498
Liabilities	2,638	2,498
Level 1 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	10,910	19,014
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	3,339	1,176
Short-term investments	121,629	136,900
Long-term investments	330,966	284,821
Assets	455,934	422,897
Level 2 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	1,099
Short-term investments	19,620	6,478
Level 2 | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	2,240	1,176
Short-term investments	63,772	86,578
Long-term investments	296,370	167,140
Level 2 | Municipal debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	24,319	43,844
Long-term investments	30,086	117,681
Level 2 | Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	13,918
Long-term investments	4,510
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments		0
Assets	0	0
Business Combination, Contingent Consideration, Liability, Fair Value Disclosure		95
Level 3 | Other long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments
Cost Method Investment 1 [Member] | Other long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other long-term Investments	2,000	2,000
Cost Method Investment 2 [Member] | Other long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other long-term Investments	$ 500	$ 500