Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified									12 Months Ended
	Sep. 30, 2012 Securities		Sep. 30, 2011		Sep. 30, 2012 Current Assets [Member]		Sep. 30, 2011 Current Assets [Member]		Sep. 30, 2012 Non-current Assets [Member]	Sep. 30, 2012 Corporate Bonds [Member] Current Assets [Member]		Sep. 30, 2011 Corporate Bonds [Member] Current Assets [Member]		Sep. 30, 2012 Corporate Bonds [Member] Non-current Assets [Member]		Sep. 30, 2011 Corporate Bonds [Member] Non-current Assets [Member]		Sep. 30, 2012 Commercial Paper [Member] Current Assets [Member]		Sep. 30, 2011 Commercial Paper [Member] Current Assets [Member]		Sep. 30, 2012 Certificates of Deposit [Member] Current Assets [Member]		Sep. 30, 2011 Certificates of Deposit [Member] Current Assets [Member]		Sep. 30, 2012 Government Municipal Bonds [Member] Current Assets [Member]		Sep. 30, 2011 Government Municipal Bonds [Member] Current Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities below amortized cost basis	42
Number of securities	62
Maturity period									15 months
Amortized cost	$ 60,401	[1]	$ 53,280	[2]	$ 58,382	[1]	$ 51,667	[2]		$ 39,306	[1]	$ 22,694	[2]	$ 2,019	[1]	$ 1,613	[2]	$ 2,000	[1]	$ 4,998	[2]	$ 7,262	[1]	$ 8,775	[2]	$ 9,814	[1]	$ 15,200	[2]
Unrealized gains	15		21		15		21			14		18		0		0		0		0		0		0		1		3
Unrealized losses	(28)	[3]	(174)	[4]	(25)	[3]	(164)	[4]		(19)	[3]	(144)	[4]	(3)	[3]	(10)	[4]	0	[3]	(3)	[4]	(4)	[3]	(9)	[4]	(2)	[3]	(8)	[4]
Fair Value	60,388	[1]	53,127	[2]	58,372	[1]	51,524	[2]		39,301	[1]	22,568	[2]	2,016	[1]	1,603	[2]	2,000	[1]	4,995	[2]	7,258	[1]	8,766	[2]	9,813	[1]	15,195	[2]
Purchased and accrued interest	485		478
Aggregate related fair value of securities with unrealized losses	$ 34,503		$ 43,755

[1] Included in amortized cost and fair value is purchased and accrued interest of $485.

[2] Included in amortized cost and fair value is purchased and accrued interest of $478

[3] The aggregate fair value of securities with unrealized losses as of September 30, 2012 was $34,503. These investments have been in an unrealized loss position for less than twelve months.

[4] The aggregate fair value of securities with unrealized losses as of September 30, 2011 was $43,755. These investments have been in an unrealized loss position for less than twelve months.