Note 3 - Short-term Investments - Summary of Short-term Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023
Investments, amortized cost	$ 30,463	$ 14,932
Investments, unrealized gains	0	4
Investments, unrealized losses	(15)	(15)
Investments, fair value	30,448	14,921
Corporate Debt Securities [Member]
Investments, amortized cost	21,937	11,310
Investments, unrealized gains	0	0
Investments, unrealized losses	(14)	(15)
Investments, fair value	21,923	11,295
US Treasury and Government Short-Term Debt Securities [Member]
Investments, amortized cost	8,526	3,622
Investments, unrealized gains	0	4
Investments, unrealized losses	(1)	0
Investments, fair value	$ 8,525	$ 3,626