Note 5 - Fair Value Measurements - Fair Value by Major Security Type (Details) - USD ($)	Dec. 31, 2019	Sep. 30, 2019
Short-term marketable securities	$ 4,181,909	$ 3,695,364
Long-term Securities	945,833	1,384,819
Fair Value, Nonrecurring [Member]
Cost Basis	5,374,274	5,344,359
Unrealized Gains (Losses)	7,876	11,362
Fair Value	5,382,150	5,355,721
Cash Equivalents	254,408	275,538
Short-term marketable securities	4,181,909	3,695,364
Long-term Securities	945,833	1,384,819
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Cost Basis	254,408	275,538
Unrealized Gains (Losses)
Fair Value	254,408	275,538
Cash Equivalents	254,408	275,538
Short-term marketable securities
Long-term Securities
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Cost Basis	5,119,866	5,068,821
Unrealized Gains (Losses)	7,876	11,362
Fair Value	5,127,742	5,080,183
Cash Equivalents
Short-term marketable securities	4,181,909	3,695,364
Long-term Securities	945,833	1,384,819
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Cost Basis	1,444,833	971,592
Unrealized Gains (Losses)
Fair Value	1,444,833	971,592
Cash Equivalents
Short-term marketable securities	499,000	499,000
Long-term Securities	945,833	472,592
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member]
Cost Basis	270,221	240,463
Unrealized Gains (Losses)	453	205
Fair Value	270,674	240,668
Cash Equivalents
Short-term marketable securities	270,674	80,336
Long-term Securities		160,332
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Cost Basis	3,404,812	3,856,766
Unrealized Gains (Losses)	7,423	11,157
Fair Value	3,412,235	3,867,923
Cash Equivalents
Short-term marketable securities	3,412,235	3,116,028
Long-term Securities		$ 751,895