Marketable Securities (Fair Value to Amortized Cost) (Details) - USD ($) $ in Thousands	Dec. 31, 2017		Sep. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	$ 32,492	[1]	$ 36,788	[2]
Available-for-sale securities, unrealized gains	1		4
Available-for-sale securities, unrealized losses	(42)		(24)
Available-for-sale marketable securities, fair value	32,451	[1]	36,768	[2]
Purchased and accrued interest	201		211
Current Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	28,230	[1]	32,031	[2]
Available-for-sale securities, unrealized gains	1		4
Available-for-sale securities, unrealized losses	(27)		(20)
Available-for-sale marketable securities, fair value	28,204	[1]	32,015	[2]
Current Assets | Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	24,217	[1]	28,275	[2]
Available-for-sale securities, unrealized gains	0		0
Available-for-sale securities, unrealized losses	(26)		(20)
Available-for-sale marketable securities, fair value	24,191	[1]	28,255	[2]
Current Assets | Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	4,013	[1]	3,756	[2]
Available-for-sale securities, unrealized gains	1		4
Available-for-sale securities, unrealized losses	(1)		0
Available-for-sale marketable securities, fair value	4,013	[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	4,262	[1]	4,757	[2]
Available-for-sale securities, unrealized gains	0		0
Available-for-sale securities, unrealized losses	(15)		(4)
Available-for-sale marketable securities, fair value	$ 4,247	[1]	$ 4,753	[2]

[1] Included in amortized cost and fair value is purchased and accrued interest of $201

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