Investments and Fair Value Measurements (Schedule Of Financial Assets Carried At Fair Value) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 25, 2015	Sep. 26, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	$ 531,926	$ 568,472
Short-term investments, cost	476,407	528,325
Short term investments, total	476,419	529,043
Long-term investments, unrealized gains		226
Long-term investments, total	321,015
Total cash, cash equivalents, and investments, cost	991,104	1,095,295
Total cash, cash equivalents, and investments, unrealized gains	1,218	854
Total cash, cash equivalents, and investments, unrealized losses	(480)	(134)
Total cash, cash equivalents, and investments, total	991,842	1,096,015
Assets	531,926	568,472
Other long-term Investments	321,015	296,335
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	30,505
Long-term investments, unrealized gains	19
Long-term investments, unrealized losses	(17)
Long-term investments, total	30,507
U.S. agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	2,000	35,443
Short-term investments, unrealized gains	1	5
Short-term investments, unrealized losses	0	(3)
Short term investments, total	2,001	35,445
Long-term investments, cost	1,999	31,980
Long-term investments, unrealized gains	1	19
Long-term investments, unrealized losses	0	(6)
Long-term investments, total	2,000	31,993
Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	6,478	21,788
Short-term investments, unrealized gains	0	0
Short-term investments, unrealized losses	0	0
Short term investments, total	6,478	21,788
Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	1,176
Short-term investments, cost	86,543	56,106
Short-term investments, unrealized gains	46	81
Short-term investments, unrealized losses	(11)	(10)
Short term investments, total	86,578	56,177
Long-term investments, cost	167,394	117,063
Long-term investments, unrealized gains	138
Long-term investments, unrealized losses	(392)	(80)
Long-term investments, total	167,140	117,209
Municipal debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	43,746	117,606
Short-term investments, unrealized gains	98	197
Short-term investments, unrealized losses	0	(5)
Short term investments, total	43,844	117,798
Long-term investments, cost	117,552
Long-term investments, unrealized gains	189
Long-term investments, unrealized losses	(60)
Long-term investments, total	117,681
Total cash, cash equivalents, and investments, cost	35,476	55,979
Other long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost Method Investment, Fair Value Measurement Adjustment	700
Long-term investments, cost	2,961	295,880
Long-term investments, unrealized gains	726	571
Long-term investments, unrealized losses	0	(116)
Long-term investments, total	3,687	296,335
Long-term investments	500
Other long-term Investments		500
Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments, cost	138,767	230,943
Short-term investments, unrealized gains	145	283
Short-term investments, unrealized losses	(11)	(18)
Short term investments, total	138,901	231,208
Long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments, cost	320,411
Long-term investments, unrealized gains	1,073
Long-term investments, unrealized losses	(469)
Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	511,736	564,745
Assets		564,745
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	19,014	1,727
Assets		1,727
Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash		2,000
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	19,014	1,727
Short-term investments	2,001	35,445
Long-term investments	33,233	31,993
Assets	54,248	69,165
Level 1 | US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments	30,507
Level 1 | U.S. agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	2,001	35,445
Long-term investments	2,000	31,993
Level 1 | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	1,176
Level 1 | Other long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term investments	726
Level 1 | Investments held in supplemental retirement plan:
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	2,498	2,507
Liabilities	2,498	2,507
Level 1 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	19,014	$ 1,727
Level 1 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	1,176	$ 2,000
Short-term investments	136,900	195,763
Long-term investments	284,821	263,842
Assets	422,897	461,605
Level 2 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash		2,000
Short-term investments	6,478	21,788
Level 2 | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	86,578	56,177
Long-term investments	167,140	117,209
Level 2 | Municipal debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	43,844	117,798
Long-term investments, cost		146,337
Long-term investments, unrealized gains		326
Long-term investments, unrealized losses		(30)
Long-term investments, total		146,633
Long-term investments	117,681	$ 146,633
Level 2 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash		$ 0
Short-term investments		0
Long-term investments	0	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		500
Long-term investments, unrealized gains		0
Long-term investments, unrealized losses		0
Long-term investments, total		$ 500
Long-term investments
Level 3 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash
Level 3 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash
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
Cost Method Investment 2 [Member] | Other long-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other long-term Investments	$ 500