Note 6 - Fair Value Measurements - Fair Value by Major Security Type (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Short-term marketable securities	$ 5,686	$ 4,265
Long-term Securities	1,875	3,805
Fair Value, Nonrecurring [Member]
Cost Basis	8,493	8,428
Unrealized Gains (Losses)	0	7
Fair Value	8,493	8,435
Cash Equivalents	932	365
Short-term marketable securities	5,686	4,265
Long-term Securities	1,875	3,805
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Cost Basis	932	365
Unrealized Gains (Losses)	0	0
Fair Value	932	365
Cash Equivalents	932	365
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Cost Basis	7,561	8,063
Unrealized Gains (Losses)	0	7
Fair Value	7,561	8,070
Cash Equivalents	0	0
Short-term marketable securities	5,686	4,265
Long-term Securities	1,875	3,805
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Cost Basis	1,494	1,195
Unrealized Gains (Losses)	0	0
Fair Value	1,494	1,195
Cash Equivalents	0	0
Short-term marketable securities	694
Long-term Securities	800	1,195
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member]
Cost Basis	5,139	3,777
Unrealized Gains (Losses)	(1)	4
Fair Value	5,138	3,781
Cash Equivalents	0	0
Short-term marketable securities	4,205	2,431
Long-term Securities	933	1,350
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Cost Basis	928	3,091
Unrealized Gains (Losses)	1	3
Fair Value	929	3,094
Cash Equivalents	0	0
Short-term marketable securities	787	1,834
Long-term Securities	$ 142	$ 1,260