Marketable Securities (Fair Value to Amortized Cost) (Details) - USD ($) $ in Thousands		Jun. 30, 2017		Sep. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis		$ 19,249	[1]	$ 61,928	[2]
Available-for-sale securities, unrealized gains		6		49
Available-for-sale securities, unrealized losses		(14)		(54)
Available-for-sale marketable securities, fair value		19,241	[1]	61,923	[2]
Purchased and accrued interest		175		271
Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis		17,242	[1]	58,423	[2]
Available-for-sale securities, unrealized gains		2		13
Available-for-sale securities, unrealized losses		(14)		(54)
Available-for-sale marketable securities, fair value		17,230	[1]	58,382	[2]
Current Assets | Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis		10,226	[1]	28,801	[2]
Available-for-sale securities, unrealized gains		0		0
Available-for-sale securities, unrealized losses		(13)		(34)
Available-for-sale marketable securities, fair value		10,213	[1]	28,767	[2]
Current Assets | Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis		2,000	[1]	23,963	[2]
Available-for-sale securities, unrealized gains		0		0
Available-for-sale securities, unrealized losses		(1)		(20)
Available-for-sale marketable securities, fair value		1,999	[1]	23,943	[2]
Current Assets | Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis		5,016	[1]	3,755	[2]
Available-for-sale securities, unrealized gains		2		13
Available-for-sale securities, unrealized losses		0		0
Available-for-sale marketable securities, fair value		5,018	[1]	3,768	[2]
Current Assets | Government municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	[2]			1,904
Available-for-sale securities, unrealized gains				0
Available-for-sale securities, unrealized losses				0
Available-for-sale marketable securities, fair value	[2]			1,904
Non-current Assets | Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis		2,007	[1]	3,505	[2]
Available-for-sale securities, unrealized gains		4		36
Available-for-sale securities, unrealized losses		0		0
Available-for-sale marketable securities, fair value		$ 2,011	[1]	$ 3,541	[2]

[1] Included in amortized cost and fair value is purchased and accrued interest of $175

[2] Included in amortized cost and fair value is purchased and accrued interest of $271.