Investments and Fair Value Measurements (Schedule Of Financial Assets Carried At Fair Value) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 29, 2017	Sep. 30, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	$ 627,017	$ 516,112
Short-term investments, cost	561,977	525,904
Short term investments, total	561,366	526,420
Long-term investments, total		393,904
Total cash, cash equivalents, and investments, cost	1,189,392	1,030,769
Total cash, cash equivalents, and investments, unrealized gains	799	1,251
Total cash, cash equivalents, and investments, unrealized losses	(1,053)	(375)
Total cash, cash equivalents, and investments, total	1,189,138	1,031,645
Assets	627,017	516,112
Other long-term Investments	314,364	393,904
US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	2,034
Short-term investments, unrealized gains	0
Short-term investments, unrealized losses	(6)
Short term investments, total	2,028
Long-term investments, cost	17,839	31,971
Long-term investments, unrealized gains	0	77
Long-term investments, unrealized losses	(107)	(12)
Long-term investments, total	17,732	32,036
U.S. agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments, cost	21,779	27,536
Long-term investments, unrealized gains	0	24
Long-term investments, unrealized losses	(178)	(26)
Long-term investments, total	21,601	27,534
Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	1,223	1,099
Short-term investments, cost	15,160	19,629
Short-term investments, unrealized gains	2	1
Short-term investments, unrealized losses	(1)	(10)
Short term investments, total	15,161	19,620
Total cash, cash equivalents, and investments, cost	4,292	11,479
Total cash, cash equivalents, and investments, unrealized gains	1	10
Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash		2,240
Short-term investments, cost	174,750	63,762
Short-term investments, unrealized gains	54	24
Short-term investments, unrealized losses	(163)	(14)
Short term investments, total	174,641	63,772
Long-term investments, cost	218,857	295,921
Long-term investments, unrealized gains	327	715
Long-term investments, unrealized losses	(537)	(266)
Long-term investments, total	218,647	296,370
Municipal debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	29,178	24,334
Short-term investments, unrealized gains	16
Short-term investments, unrealized losses	(9)	(15)
Short term investments, total	29,185	24,319
Long-term investments, cost	28,913	30,090
Long-term investments, unrealized gains	29	28
Long-term investments, unrealized losses	(25)	(32)
Long-term investments, total	28,917	30,086
Total cash, cash equivalents, and investments, cost	26,749	35,625
Other long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost Method Investment, Fair Value Measurement Adjustment	400	400
Long-term investments, cost	4,171	3,002
Long-term investments, unrealized gains	357	366
Long-term investments, unrealized losses	0
Long-term investments, total	4,528	3,368
Long-term investments	600	500
Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	247,876	121,637
Short-term investments, unrealized gains	81	31
Short-term investments, unrealized losses	(200)	(39)
Short term investments, total	247,757	121,629
Long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments, cost	314,499	393,020
Long-term investments, unrealized gains	718	1,220
Long-term investments, unrealized losses	(853)	(336)
Long-term investments, total	314,364
Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	17,236	13,912
Short-term investments, unrealized gains	9	6
Short-term investments, unrealized losses	(1)
Short term investments, total	17,244	13,918
Long-term investments, cost	22,940	4,500
Long-term investments, unrealized gains	5	10
Long-term investments, unrealized losses	(6)
Long-term investments, total	22,939	4,510
US Government Agencies Short-term Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	9,518
Short-term investments, unrealized gains	0
Short-term investments, unrealized losses	(20)
Short term investments, total	9,498
Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	623,244	501,863
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	2,550	10,910
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	2,550	10,910
Short-term investments	2,028	0
Long-term investments	18,089	59,936
Assets	22,667	70,846
Level 1 | US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	2,028
Long-term investments	17,732	32,036
Level 1 | U.S. agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments		27,534
Level 1 | Other long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments	357	366
Level 1 | Investments held in supplemental retirement plan:
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	3,026	2,638
Liabilities	3,026	2,638
Level 1 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	2,550	10,910
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	1,223	3,339
Short-term investments	245,729	121,629
Long-term investments	292,104	330,966
Assets	539,056	455,934
Level 2 | U.S. agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments	21,601
Level 2 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	1,223	1,099
Short-term investments	15,161	19,620
Level 2 | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash		2,240
Short-term investments	174,641	63,772
Long-term investments	218,647	296,370
Level 2 | Municipal debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	29,185	24,319
Long-term investments	28,917	30,086
Level 2 | Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	17,244	13,918
Long-term investments	22,939	4,510
Level 2 | US Government Agencies Short-term Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	9,498
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	0	0
Cost Method Investment 1 [Member] | Other long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other long-term Investments	3,000	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