Marketable Securities - Summary of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 36,965	$ 53,629
Gross Unrealized Losses	(2)	(112)
Gross Unrealized Gains	6	1
Fair Value	36,969	53,518
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	31,863	30,142
Gross Unrealized Losses	(2)	(65)
Gross Unrealized Gains	5
Fair Value	31,866	30,077
Bank certificates of deposits
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	750	5,148
Gross Unrealized Gains		1
Fair Value	750	5,149
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,317	14,763
Gross Unrealized Losses		(30)
Gross Unrealized Gains	1
Fair Value	4,318	14,733
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		2,797
Gross Unrealized Losses		(17)
Fair Value		2,780
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	35	779
Fair Value	$ 35	$ 779

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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