Investments - Summary of Investments by Type of Security (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Sep. 30, 2021
Debt Securities, Available-for-sale [Line Items]
Cost	$ 70,314	$ 197,165
Gross Unrealized Gains	0	12
Gross Unrealized Losses	(1,413)	(69)
Fair Market Value	68,901	197,108
Short-term | U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Cost	6,016	4,222
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(134)	0
Fair Market Value	5,882	4,223
Short-term | Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Cost		4,812
Gross Unrealized Gains		1
Gross Unrealized Losses		(2)
Fair Market Value		4,811
Short-term | Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Cost	2,865
Gross Unrealized Gains	0
Gross Unrealized Losses	(38)
Fair Market Value	2,827
Short-term | Commercial paper
Debt Securities, Available-for-sale [Line Items]
Cost	18,245
Gross Unrealized Gains	0
Gross Unrealized Losses	(223)
Fair Market Value	18,022
Short-term | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Cost	32,065	140,042
Gross Unrealized Gains	0	6
Gross Unrealized Losses	(528)	(25)
Fair Market Value	31,537	140,023
Long-term | U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Cost	3,431	6,996
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(210)	(2)
Fair Market Value	3,221	6,995
Long-term | Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Cost	0	2,909
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(1)
Fair Market Value	0	2,908
Long-term | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Cost	7,692	38,184
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(280)	(39)
Fair Market Value	$ 7,412	$ 38,148