Marketable Securities (Fair Value to Amortized Cost) (Details) - USD ($) $ in Thousands		Mar. 31, 2018		Sep. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis		$ 7,275	[1]	$ 36,788	[2]
Available-for-sale securities, unrealized gains		0		4
Available-for-sale securities, unrealized losses		(29)		(24)
Available-for-sale marketable securities, fair value		7,246	[1]	36,768	[2]
Purchased and accrued interest		25		211
Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	[2]			32,031
Available-for-sale securities, unrealized gains				4
Available-for-sale securities, unrealized losses				(20)
Available-for-sale marketable securities, fair value	[2]			32,015
Current Assets | Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	[2]			28,275
Available-for-sale securities, unrealized gains				0
Available-for-sale securities, unrealized losses				(20)
Available-for-sale marketable securities, fair value	[2]			28,255
Current Assets | Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis		4,766	[1]	3,756	[2]
Available-for-sale securities, unrealized gains		0		4
Available-for-sale securities, unrealized losses		(9)		0
Available-for-sale marketable securities, fair value		4,757	[1]	3,760	[2]
Non-current Assets | Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis		2,509	[1]	4,757	[2]
Available-for-sale securities, unrealized gains		0		0
Available-for-sale securities, unrealized losses		(20)		(4)
Available-for-sale marketable securities, fair value		$ 2,489	[1]	$ 4,753	[2]

[1] Included in amortized cost and fair value is purchased and accrued interest of $25

[2] Included in amortized cost and fair value is purchased and accrued interest of $211.