Marketable Securities - Summary of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 51,244	$ 2,670
Gross Unrealized Losses	(83)
Gross Unrealized Gains	2
Fair Value	51,163	2,670
U.S. Treasury securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	31,870
Gross Unrealized Losses	(56)
Fair Value	31,814
Bank certificates of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,158
Gross Unrealized Gains	2
Fair Value	6,160
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,426	2,642
Gross Unrealized Losses	(17)
Fair Value	6,409	2,642
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,761
Gross Unrealized Losses	(10)
Fair Value	6,751
Other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29	28
Fair Value	$ 29	$ 28

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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

+ References

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
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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
-Topic 320
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-Section 50
-Paragraph 2
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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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