Short-Term Investments (Details) (USD $)	3 Months Ended
	Dec. 29, 2012	Dec. 31, 2011	Sep. 29, 2012
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Cash and cash equivalent, Cost Basis	$ 87,980,000		$ 67,752,000
Cash and cash equivalent, Unrealized Gains	16,000		9,000
Cash and cash equivalent, Unrealized Losses	0		0
Cash and cash equivalent, Fair Value	87,996,000		67,761,000
Available-for-sale securities: Cost Basis	91,328,000		156,217,000
Available-for-sale securities: Unrealized Gains	454,000		954,000
Available-for-sale securities: Unrealized Losses	(1,000)		(3,000)
Available-for-sale securities: Fair Value	91,781,000		157,168,000
Available-for-sale Securities, Debt Maturities [Abstract]
Due in less than 1 year, Amortized Cost	89,320,000		154,200,000
Due in less than 1 year, Estimated Fair Value	89,760,000		155,149,000
Proceeds from sale of available-for-sale securities	56,600,000	27,500,000
Gross unrealized losses on investments with unrealized losses that are deemed to be availble-for-sale securities	2,000
Maximum [Member]
Available-for-sale Securities, Debt Maturities [Abstract]
Realized gross gains from sale of available-for-sale securities	100,000	100,000
Certificates of deposit
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale securities: Cost Basis	2,008,000		2,017,000
Available-for-sale securities: Unrealized Gains	13,000		2,000
Available-for-sale securities: Unrealized Losses	0		0
Available-for-sale securities: Fair Value	2,021,000		2,019,000
US Treasury and agency obligations
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale securities: Cost Basis	81,272,000		108,284,000
Available-for-sale securities: Unrealized Gains	359,000		666,000
Available-for-sale securities: Unrealized Losses	0		(2,000)
Available-for-sale securities: Fair Value	81,631,000		108,948,000
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	8,048,000		41,912,000
Available-for-sale securities: Unrealized Gains	82,000		272,000
Available-for-sale securities: Unrealized Losses	(1,000)		(1,000)
Available-for-sale securities: Fair Value	8,129,000		42,183,000
Available-for-sale Securities, Debt Maturities [Abstract]
Total investments in available-for-sale debt securities, Estimated Fair Value	6,700,000
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