INVESTMENTS - Investments by Type of Security (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Sep. 30, 2023
Debt Securities, Available-for-sale [Line Items]
Cost	$ 48,980	$ 76,245
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(105)	(242)
Fair Market Value	48,875	76,004
Short-Term | U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Cost	3,814	40,329
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(24)	(76)
Fair Market Value	3,790	40,254
Short-Term | U.S. Government and agency securities, short-term
Debt Securities, Available-for-sale [Line Items]
Cost	6,722
Gross Unrealized Gains	0
Gross Unrealized Losses	(4)
Fair Market Value	6,718
Short-Term | Commercial paper, short-term
Debt Securities, Available-for-sale [Line Items]
Cost	15,723
Gross Unrealized Gains	0
Gross Unrealized Losses	(12)
Fair Market Value	15,711
Short-Term | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Cost	12,538	34,545
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(39)	(99)
Fair Market Value	12,499	34,446
Long-Term | U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Cost	0	1,371
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(67)
Fair Market Value	0	$ 1,304
Long-Term | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Cost	10,183
Gross Unrealized Gains	0
Gross Unrealized Losses	(26)
Fair Market Value	10,157
Long-Term | Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Cost	0
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Market Value	$ 0