Note 5 - Fair Value Measurements - Fair Value by Major Security Type (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Sep. 30, 2022
Short-term marketable securities	$ 3,549	$ 6,397
Long-term Securities	392	781
Fair Value, Nonrecurring [Member]
Cost Basis	4,755	8,584
Unrealized Loss	(19)	90
Unrealized Loss	19	(90)
Fair Value	4,736	8,494
Cash Equivalents	795	1,316
Short-term marketable securities	3,549	6,397
Long-term Securities	392	781
Fair Value, Inputs, Level 1 [Member] | Fair Value, Nonrecurring [Member]
Cost Basis	795	1,316
Unrealized Loss	0	0
Unrealized Loss	(0)	0
Fair Value	795	1,316
Cash Equivalents	795	1,316
Short-term marketable securities		0
Long-term Securities		0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Nonrecurring [Member]
Cost Basis	3,960	7,268
Unrealized Loss	(19)	90
Unrealized Loss	19	(90)
Fair Value	3,941	7,178
Cash Equivalents	0	0
Short-term marketable securities	3,549	6,397
Long-term Securities	392	781
Fair Value, Inputs, Level 2 [Member] | Fair Value, Nonrecurring [Member] | Certificates of Deposit [Member]
Cost Basis	302	800
Unrealized Loss	0	0
Unrealized Loss	(0)	0
Fair Value	302	800
Cash Equivalents	0	0
Short-term marketable securities	0	498
Long-term Securities	302	302
Fair Value, Inputs, Level 2 [Member] | Fair Value, Nonrecurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Cost Basis	2,747	4,066
Unrealized Loss	(12)	65
Unrealized Loss	12	(65)
Fair Value	2,735	4,001
Cash Equivalents	0	0
Short-term marketable securities	2,645	3,772
Long-term Securities	90	229
Fair Value, Inputs, Level 2 [Member] | Fair Value, Nonrecurring [Member] | Corporate Debt Securities [Member]
Cost Basis	911	2,402
Unrealized Loss	(7)	25
Unrealized Loss	7	(25)
Fair Value	904	2,377
Cash Equivalents	0	0
Short-term marketable securities	904	2,127
Long-term Securities	$ 0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Nonrecurring [Member] | Convertible Debt Securities [Member]
Long-term Securities		$ 250