Marketable Securities - Summary of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Sep. 30, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,717	$ 36,965
Gross Unrealized Losses		(2)
Gross Unrealized Gains		6
Fair Value	2,717	36,969
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		31,863
Gross Unrealized Losses		(2)
Gross Unrealized Gains		5
Fair Value		31,866
Bank certificates of deposits
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	101	750
Fair Value	101	750
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,555	4,317
Gross Unrealized Gains		1
Fair Value	2,555	4,318
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	61	35
Fair Value	$ 61	$ 35

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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