Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended
	Mar. 31, 2014 Securities		Mar. 31, 2013	Mar. 31, 2014 Securities		Mar. 31, 2013	Sep. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Number of securities below amortized cost basis	34			34
Number of securities	72			72
Proceeds from maturities of marketable securities	$ 6,700		$ 20,700	$ 13,778		$ 38,161
Available-for-sale securities, amortized cost basis	55,850	[1]		55,850	[1]		64,471	[2]
Available-for-sale securities, unrealized gains	26			26			10
Available-for-sale debt securities, unrealized losses	(37)			(37)			(86)
Available-for-sale marketable securities, fair value	55,839	[1]		55,839	[1]		64,395	[2]
Purchased and accrued interest	583			583			629
Fair value of available-for-sale securities in continuous unrealized loss position for less than twelve months	24,585			24,585			48,544
Unrealized losses of available-for-sale securities in continuous unrealized loss position for less than twelve months	(26)			(26)			(85)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer	11,477			11,477			2,001
Unrealized losses of available-for-sale securities in continuous unrealized loss position for twelve months or longer	(11)			(11)			(1)
Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, next twelve months, maximum year mature	1 year			1 year
Available-for-sale securities, amortized cost basis	45,048	[1]		45,048	[1]		47,029	[2]
Available-for-sale securities, unrealized gains	11			11			10
Available-for-sale debt securities, unrealized losses	(24)			(24)			(33)
Available-for-sale marketable securities, fair value	45,035	[1]		45,035	[1]		47,006	[2]
Non-current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, year two through five, maximum year mature	3 years			3 years
Available-for-sale securities, amortized cost basis	10,802	[1]		10,802	[1]		17,442	[2]
Available-for-sale securities, unrealized gains	15			15			0
Available-for-sale debt securities, unrealized losses	(13)			(13)			(53)
Available-for-sale marketable securities, fair value	10,804	[1]		10,804	[1]		17,389	[2]
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	21,587			21,587			29,911
Unrealized losses of available-for-sale securities in continuous unrealized loss position for less than twelve months	(24)			(24)			(35)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer	10,730			10,730			2,001
Unrealized losses of available-for-sale securities in continuous unrealized loss position for twelve months or longer	(8)			(8)			(1)
Corporate Bonds | Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	36,180	[1]		36,180	[1]		35,161	[2]
Available-for-sale securities, unrealized gains	10			10			10
Available-for-sale debt securities, unrealized losses	(24)			(24)			(30)
Available-for-sale marketable securities, fair value	36,166	[1]		36,166	[1]		35,141	[2]
Corporate Bonds | Non-current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	2,050	[1]		2,050	[1]		6,439	[2]
Available-for-sale securities, unrealized gains	0			0			0
Available-for-sale debt securities, unrealized losses	(8)			(8)			(6)
Available-for-sale marketable securities, fair value	2,042	[1]		2,042	[1]		6,433	[2]
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	2,998			2,998			12,451
Unrealized losses of available-for-sale securities in continuous unrealized loss position for less than twelve months	(2)			(2)			(49)
Fair value of available-for-sale securities in continuous unrealized loss position for twelve months or longer	747			747			0
Unrealized losses of available-for-sale securities in continuous unrealized loss position for twelve months or longer	(3)			(3)			0
Certificates of Deposit | Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	2,752	[1]		2,752	[1]		1,753	[2]
Available-for-sale securities, unrealized gains	0			0			0
Available-for-sale debt securities, unrealized losses	0			0			(2)
Available-for-sale marketable securities, fair value	2,752	[1]		2,752	[1]		1,751	[2]
Certificates of Deposit | Non-current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	8,752	[1]		8,752	[1]		11,003	[2]
Available-for-sale securities, unrealized gains	15			15			0
Available-for-sale debt securities, unrealized losses	(5)			(5)			(47)
Available-for-sale marketable securities, fair value	8,762	[1]		8,762	[1]		10,956	[2]
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
Unrealized losses of available-for-sale securities in continuous unrealized loss position for less than twelve months							(1)
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
Government Municipal Bonds | Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	6,116	[1]		6,116	[1]		10,115	[2]
Available-for-sale securities, unrealized gains	1			1			0
Available-for-sale debt securities, unrealized losses	0			0			(1)
Available-for-sale marketable securities, fair value	$ 6,117	[1]		$ 6,117	[1]		$ 10,114	[2]

[1] Included in amortized cost and fair value is purchased and accrued interest of $583

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