Marketable Securities (Amortized Cost and Fair Value of Marketable Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 54,695	$ 50,458
Gross unrealized gains	0	2
Gross unrealized losses	(523)	(145)
Fair value	54,172	50,315
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	221	240
Gross unrealized gains	0	0
Gross unrealized losses	(2)	0
Fair value	219	240
Corporate notes/bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	53,474	47,811
Gross unrealized gains	0	2
Gross unrealized losses	(512)	(140)
Fair value	52,962	47,673
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,000	2,407
Gross unrealized gains	0	0
Gross unrealized losses	(9)	(5)
Fair value	$ 991	$ 2,402

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 2
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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