Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2013 Securities		Sep. 30, 2012		Sep. 30, 2011
Schedule of Available-for-sale Securities [Line Items]
Number of securities below amortized cost basis	72
Number of securities	80
Proceeds from maturities of marketable securities	$ 63,089		$ 65,533		$ 44,843
Available-for-sale Securities, Amortized Cost Basis	64,471	[1]	60,401	[2]
Unrealized gains	10		15
Unrealized losses	(86)		(28)
Available-for-sale marketable securities	64,395	[1]	60,388	[2]
Purchased and accrued interest	629		485
Fair value of available-for-sale securities in continuous unrealized loss position for less than twelve months	48,544		34,503
Unrealized losses of available-for-sale securities in continuous unrealized loss position for less than twelve months	(85)		(28)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer	2,001		0
Unrealized losses of available-for-sale securities in continuous unrealized loss position for twelve months or longer	(1)		0
Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, next twelve months, maximum year mature	1 year
Available-for-sale Securities, Amortized Cost Basis	47,029		58,382
Unrealized gains	10		15
Unrealized losses	(33)		(25)
Available-for-sale marketable securities	47,006		58,372
Non-current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, year two through five, maximum year mature	3 years
Available-for-sale Securities, Amortized Cost Basis	17,442
Unrealized gains	0
Unrealized losses	(53)
Available-for-sale marketable securities	17,389
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in continuous unrealized loss position for less than twelve months	29,911		6,246
Unrealized losses of available-for-sale securities in continuous unrealized loss position for less than twelve months	(35)		(22)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer	2,001		0
Unrealized losses of available-for-sale securities in continuous unrealized loss position for twelve months or longer	(1)		0
Corporate Bonds | Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	35,161		39,306
Unrealized gains	10		14
Unrealized losses	(30)		(19)
Available-for-sale marketable securities	35,141		39,301
Corporate Bonds | Non-current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	6,439		2,019
Unrealized gains	0		0
Unrealized losses	(6)		(3)
Available-for-sale marketable securities	6,433		2,016
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in continuous unrealized loss position for less than twelve months			2,000
Unrealized losses of available-for-sale securities in continuous unrealized loss position for less than twelve months			0
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer			0
Unrealized losses of available-for-sale securities in continuous unrealized loss position for twelve months or longer			0
Commercial Paper | Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis			2,000
Unrealized gains			0
Unrealized losses			0
Available-for-sale marketable securities			2,000
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in continuous unrealized loss position for less than twelve months	12,451		5,114
Unrealized losses of available-for-sale securities in continuous unrealized loss position for less than twelve months	(49)		(4)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer	0		0
Unrealized losses of available-for-sale securities in continuous unrealized loss position for twelve months or longer	0		0
Certificates of Deposit | Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,753		7,262
Unrealized gains	0		0
Unrealized losses	(2)		(4)
Available-for-sale marketable securities	1,751		7,258
Certificates of Deposit | Non-current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	11,003
Unrealized gains	0
Unrealized losses	(47)
Available-for-sale marketable securities	10,956
Government Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in continuous unrealized loss position for less than twelve months	6,182		21,143
Unrealized losses of available-for-sale securities in continuous unrealized loss position for less than twelve months	(1)		(2)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer	0		0
Unrealized losses of available-for-sale securities in continuous unrealized loss position for twelve months or longer	0		0
Government Municipal Bonds | Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	10,115		9,814
Unrealized gains	0		1
Unrealized losses	(1)		(2)
Available-for-sale marketable securities	$ 10,114		$ 9,813

[1] Included in amortized cost and fair value is purchased and accrued interest of $629.

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