Short-Term Investments (Details) (USD $)	3 Months Ended		9 Months Ended
	Jun. 29, 2013	Jun. 30, 2012	Jun. 29, 2013	Jun. 30, 2012	Sep. 29, 2012
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Cash and cash equivalent, Cost Basis	$ 81,311,000		$ 81,311,000		$ 67,752,000
Cash and cash equivalent, Unrealized Gains	0		0		9,000
Cash and cash equivalent, Unrealized Losses	0		0		0
Cash and cash equivalent, Fair Value	81,311,000		81,311,000		67,761,000
Available-for-sale securities: Cost Basis	119,885,000		119,885,000		156,217,000
Available-for-sale securities: Unrealized Gains	504,000		504,000		954,000
Available-for-sale securities: Unrealized Losses	(18,000)		(18,000)		(3,000)
Available-for-sale securities: Fair Value	120,371,000		120,371,000		157,168,000
Available-for-sale Securities, Debt Maturities [Abstract]
Due in less than 1 year, Amortized Cost	119,885,000		119,885,000		154,200,000
Due in less than 1 year, Estimated Fair Value	120,371,000		120,371,000		155,149,000
Proceeds from sale of available-for-sale securities	3,000,000	16,800,000	68,700,000	76,900,000
Gross unrealized losses on investments with unrealized losses that are deemed to be availble-for-sale securities			18,000
Maximum [Member]
Available-for-sale Securities, Debt Maturities [Abstract]
Realized gross gains from sale of available-for-sale securities	100,000	100,000	100,000	100,000
Certificates of deposit
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale securities: Cost Basis	9,994,000		9,994,000		2,017,000
Available-for-sale securities: Unrealized Gains	0		0		2,000
Available-for-sale securities: Unrealized Losses	0		0		0
Available-for-sale securities: Fair Value	9,994,000		9,994,000		2,019,000
US Treasury and agency obligations
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale securities: Cost Basis	94,577,000		94,577,000		108,284,000
Available-for-sale securities: Unrealized Gains	468,000		468,000		666,000
Available-for-sale securities: Unrealized Losses	(5,000)		(5,000)		(2,000)
Available-for-sale securities: Fair Value	95,040,000		95,040,000		108,948,000
Available-for-sale Securities, Debt Maturities [Abstract]
Total investments in available-for-sale debt securities, Estimated Fair Value	47,700,000		47,700,000
International government obligations [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale securities: Cost Basis					2,004,000
Available-for-sale securities: Unrealized Gains					14,000
Available-for-sale securities: Unrealized Losses					0
Available-for-sale securities: Fair Value					2,018,000
Corporate notes and obligations
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale securities: Cost Basis	15,314,000		15,314,000		41,912,000
Available-for-sale securities: Unrealized Gains	36,000		36,000		272,000
Available-for-sale securities: Unrealized Losses	(13,000)		(13,000)		(1,000)
Available-for-sale securities: Fair Value	15,337,000		15,337,000		42,183,000
Available-for-sale Securities, Debt Maturities [Abstract]
Total investments in available-for-sale debt securities, Estimated Fair Value	16,200,000		16,200,000
Commercial Paper [Member]
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale securities: Cost Basis					2,000,000
Available-for-sale securities: Unrealized Gains					0
Available-for-sale securities: Unrealized Losses					0
Available-for-sale securities: Fair Value					$ 2,000,000