Investments & Fair Value Measurements (Schedule Of Financial Assets and Liabilities Carried At Fair Value) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 29, 2017	Dec. 30, 2016	Sep. 29, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 596,391		$ 627,017
Cash and Cash Equivalents, Period Increase (Decrease)	30,627	$ 3,274
Available-for-sale Debt Securities, Amortized Cost Basis	563,353		561,977
Available-for-sale Securities, Debt Securities	561,124		561,366
Investment Owned, Unrecognized Unrealized Depreciation	(2,416)		(1,053)
Cash Cash Equivalents And Investments Total	1,152,498		1,189,138
Financial assets carried at fair value	596,390		627,017
Restricted Cash and Cash Equivalents	7,630		7,351
Long-term investments	303,501		314,364
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	305,600		211,423
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,219)		(437)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	153,007		129,546
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,195)		(616)
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis	259,529		251,649
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value	259,137		251,530
Available For Sale Securities Debt Maturities After One Through Two Years Amortized Cost	183,876		213,555
Available For Sale Securities Debt Maturities After One Through Two Years Fair Value	182,787		213,154
Available For Sale Securities Debt Maturities After Two Through Three Years Amortized Cost	119,948		96,773
Available For Sale Securities Debt Maturities After Two Through Three Years Fair Value	119,200		96,682
Investment Owned, at Cost	1,154,434		1,189,392
Investment Owned, Unrecognized Unrealized Appreciation	480		799
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	2,787		2,550
Financial assets carried at fair value	24,363		22,667
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	6,467		1,223
Financial assets carried at fair value	537,055		539,056
Cash [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	587,136		623,244
Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	5,865
Cash Equivalents, at Carrying Value	5,866
Cash and Cash Equivalents, Period Increase (Decrease)	(1)
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	2,787		2,550
Money Market Funds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	2,787		2,550
Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	602
Available-for-sale Debt Securities, Gross Unrealized Loss			(1)
Available-for-sale Debt Securities Gross Unrealized Gain			9
Available-for-sale Securities, Amortized Cost Basis			22,940
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	12,323		19,750
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(3)		(6)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0		0
Certificates of Deposit [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	602
Investments, Fair Value Disclosure			17,244
Investments, Noncurrent, Fair Value Disclosure			22,939
U.S. Agency Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis			21,779
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	6,177		19,713
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(53)		(91)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	22,243		11,386
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(253)		(108)
U.S. Agency Securities [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure
U.S. Agency Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure			21,601
US Government Agencies Short-term Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Gross Unrealized Loss	(33)		(20)
Available-for-sale Securities, Debt Securities	8,410		9,498
Available-for-sale Debt Securities Gross Unrealized Gain			0
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	8,410		9,498
Government Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Gross Unrealized Loss			(6)
Available-for-sale Debt Securities Gross Unrealized Gain			0
Available-for-sale Securities, Amortized Cost Basis			17,839
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	10,892		15,029
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(112)		(64)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	7,412		4,729
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(111)		(49)
Government Bonds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure			17,732
Commercial Paper [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure			1,223
Available-for-sale Debt Securities, Gross Unrealized Loss			(1)
Available-for-sale Debt Securities, Amortized Cost Basis			15,160
Available-for-sale Debt Securities Gross Unrealized Gain			2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0		0
Investment Owned, at Cost	10,015		4,292
Investment Owned, Unrecognized Unrealized Appreciation	15		1
Commercial Paper [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure			1,223
Investments, Fair Value Disclosure			15,161
Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure			2,550
Available-for-sale Debt Securities, Gross Unrealized Loss			(163)
Available-for-sale Debt Securities, Amortized Cost Basis			174,750
Available-for-sale Debt Securities Gross Unrealized Gain			54
Available-for-sale Securities, Amortized Cost Basis			218,857
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	210,057		125,890
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(800)		(251)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	119,766		109,806
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(808)		(449)
Corporate Debt Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	5,865
Investments, Fair Value Disclosure			174,641
Investments, Noncurrent, Fair Value Disclosure			218,647
Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Gross Unrealized Loss			(9)
Available-for-sale Debt Securities, Amortized Cost Basis			29,178
Available-for-sale Debt Securities Gross Unrealized Gain			16
Available-for-sale Securities, Amortized Cost Basis			28,913
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(236)		(24)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	3,586		3,625
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(23)		(10)
Investment Owned, at Cost	56,136		26,749
Municipal Bonds [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure			29,185
Investments, Noncurrent, Fair Value Disclosure			28,917
Short-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain			81
Other Long-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost Method Investment, Fair Value Measurement Adjustment	300		400
Available-for-sale Securities, Amortized Cost Basis			4,171
Investments, Noncurrent, Fair Value Disclosure	400		600
Other Long-term Investments [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure			357
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	3,165		3,026
Financial liabilities carried at fair value	3,165		3,026
Cost Method Investment 1 [Member] | Other Long-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments	3,000		3,000
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
Short-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Gross Unrealized Loss			(200)
Available-for-sale Debt Securities, Amortized Cost Basis			247,876
Available-for-sale Securities, Debt Securities			247,757
Short-term Investments [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	533		2,028
Short-term Investments [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	252,074		245,729
Short-term Investments [Member] | Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Gross Unrealized Loss	(2)
Available-for-sale Debt Securities, Amortized Cost Basis	22,981		17,236
Available-for-sale Securities, Debt Securities	22,986
Available-for-sale Debt Securities Gross Unrealized Gain	7
Available-for-sale Securities			17,244
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	22,986
Short-term Investments [Member] | U.S. Agency Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	8,443		9,518
Short-term Investments [Member] | Government Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Gross Unrealized Loss	(2)
Available-for-sale Debt Securities, Amortized Cost Basis	535		2,034
Available-for-sale Securities, Debt Securities	533		2,028
Short-term Investments [Member] | Government Bonds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	533		2,028
Short-term Investments [Member] | Commercial Paper [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Gross Unrealized Loss	(15)
Available-for-sale Debt Securities, Amortized Cost Basis	13,636
Available-for-sale Securities, Debt Securities	13,621		15,161
Available-for-sale Debt Securities Gross Unrealized Gain	0
Short-term Investments [Member] | Commercial Paper [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	13,621
Short-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Gross Unrealized Loss	(295)
Available-for-sale Debt Securities, Amortized Cost Basis	170,740
Available-for-sale Securities, Debt Securities	170,470		174,641
Available-for-sale Debt Securities Gross Unrealized Gain	25
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	170,470
Short-term Investments [Member] | Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Gross Unrealized Loss	(92)
Available-for-sale Debt Securities, Amortized Cost Basis	36,679
Available-for-sale Securities, Debt Securities	36,587		29,185
Available-for-sale Debt Securities Gross Unrealized Gain	0
Short-term Investments [Member] | Municipal Bonds [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Fair Value Disclosure	36,587
Short-term Investments [Member] | Short-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Debt Securities, Gross Unrealized Loss	(439)
Available-for-sale Debt Securities, Amortized Cost Basis	253,014
Available-for-sale Securities, Debt Securities	252,607
Available-for-sale Debt Securities Gross Unrealized Gain	32
Long-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis			314,499
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax			718
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax			(853)
Available-for-sale Securities			314,364
Long-term Investments [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	21,043		18,089
Long-term Investments [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	278,514		292,104
Long-term Investments [Member] | Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	10,345
Available-for-sale Securities	10,344		22,939
Available-for-sale Securities, Gross Unrealized Gain			5
Available-for-sale Securities, Gross Unrealized Loss	1		6
Long-term Investments [Member] | Certificates of Deposit [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, Noncurrent, Fair Value Disclosure	10,344
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	20,283
Available-for-sale Securities	20,011		21,601
Available-for-sale Securities, Gross Unrealized Gain			0
Available-for-sale Securities, Gross Unrealized Loss	272		178
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	20,011
Long-term Investments [Member] | Government Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	20,965
Available-for-sale Securities	20,747		17,732
Available-for-sale Securities, Gross Unrealized Gain	4		0
Available-for-sale Securities, Gross Unrealized Loss	222		107
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	20,747
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	225,639
Available-for-sale Securities	224,473		218,647
Available-for-sale Securities, Gross Unrealized Gain	147		327
Available-for-sale Securities, Gross Unrealized Loss	1,313		537
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	224,473
Long-term Investments [Member] | Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Amortized Cost Basis	23,853
Available-for-sale Securities	23,686		28,917
Available-for-sale Securities, Gross Unrealized Gain	1		29
Available-for-sale Securities, Gross Unrealized Loss	168		25
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	23,686
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	3,944
Available-for-sale Securities	4,240		4,528
Available-for-sale Securities, Gross Unrealized Gain	296		357
Available-for-sale Securities, Gross Unrealized Loss			$ 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	296
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	305,029
Available-for-sale Securities	303,501
Available-for-sale Securities, Gross Unrealized Gain	448
Available-for-sale Securities, Gross Unrealized Loss	$ 1,976