Investments - Summary of Investments by Type of Security (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Schedule Of Available For Sale Securities [Line Items]
Cost	$ 25,069	$ 18,051
Gross Unrealized Gains	8	4
Gross Unrealized Losses	(1)	(1)
Fair Market Value	25,076	18,054
Short-term investments \| U.S. Treasury
Schedule Of Available For Sale Securities [Line Items]
Cost	5,217	4,240
Gross Unrealized Gains	3	2
Gross Unrealized Losses	(1)	0
Fair Market Value	5,219	4,242
Short-term investments \| Asset-backed securities
Schedule Of Available For Sale Securities [Line Items]
Cost	801
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Market Value	801
Short-term investments \| Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Cost	12,248	12,258
Gross Unrealized Gains	3	2
Gross Unrealized Losses	0	0
Fair Market Value	12,251	12,260
Long-term investments \| U.S. Treasury
Schedule Of Available For Sale Securities [Line Items]
Cost	4,033	1,102
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	(1)
Fair Market Value	4,034	1,101
Long-term investments \| Asset-backed securities
Schedule Of Available For Sale Securities [Line Items]
Cost	2,116
Gross Unrealized Gains	1
Gross Unrealized Losses	0
Fair Market Value	2,117
Long-term investments \| Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Cost	654	451
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Market Value	$ 654	$ 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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