Investments - Summary of Investments by Type of Security (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Schedule Of Available For Sale Securities [Line Items]
Cost	$ 33,061	$ 18,051
Gross Unrealized Gains	162	4
Gross Unrealized Losses	0	(1)
Fair Market Value	33,223	18,054
Short-term investments \| U.S. Treasury
Schedule Of Available For Sale Securities [Line Items]
Cost	8,245	4,240
Gross Unrealized Gains	62	2
Gross Unrealized Losses	0	0
Fair Market Value	8,307	4,242
Short-term investments \| Asset-backed securities
Schedule Of Available For Sale Securities [Line Items]
Cost	3,769
Gross Unrealized Gains	34
Gross Unrealized Losses	0
Fair Market Value	3,803
Short-term investments \| Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Cost	18,147	12,258
Gross Unrealized Gains	24	2
Gross Unrealized Losses	0	0
Fair Market Value	18,171	12,260
Long-term investments \| U.S. Treasury
Schedule Of Available For Sale Securities [Line Items]
Cost		1,102
Gross Unrealized Gains		0
Gross Unrealized Losses		(1)
Fair Market Value		1,101
Long-term investments \| Asset-backed securities
Schedule Of Available For Sale Securities [Line Items]
Cost	964
Gross Unrealized Gains	14
Gross Unrealized Losses	0
Fair Market Value	978
Long-term investments \| Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Cost	1,936	451
Gross Unrealized Gains	28	0
Gross Unrealized Losses	0	0
Fair Market Value	$ 1,964	$ 451

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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