Note 6 - Fair Value Measurements - Fair Value by Major Security Type (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Short-term marketable securities	$ 5,474	$ 4,265
Long-term Securities	2,450	3,805
Fair Value, Nonrecurring [Member]
Cost Basis	8,461	8,428
Unrealized Gains (Losses)	1	7
Fair Value	8,462	8,435
Cash Equivalents	538	365
Short-term marketable securities	5,474	4,265
Long-term Securities	2,450	3,805
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Cost Basis	538	365
Unrealized Gains (Losses)
Fair Value	538	365
Cash Equivalents	538	365
Short-term marketable securities
Long-term Securities
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Cost Basis	7,923	8,063
Unrealized Gains (Losses)	1	7
Fair Value	7,924	8,070
Cash Equivalents
Short-term marketable securities	5,474	4,265
Long-term Securities	2,450	3,805
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Certificates of Deposit [Member]
Cost Basis	1,193	1,195
Unrealized Gains (Losses)
Fair Value	1,193	1,195
Cash Equivalents
Short-term marketable securities	251
Long-term Securities	942	1,195
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| US States and Political Subdivisions Debt Securities [Member]
Cost Basis	5,223	3,777
Unrealized Gains (Losses)	1	4
Fair Value	5,224	3,781
Cash Equivalents
Short-term marketable securities	4,161	2,432
Long-term Securities	1,063	1,350
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Cost Basis	1,507	3,091
Unrealized Gains (Losses)		3
Fair Value	1,507	3,094
Cash Equivalents
Short-term marketable securities	1,062	1,833
Long-term Securities	$ 445	$ 1,260

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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Amount before tax of unrealized gain (loss) in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of investment in marketable security, classified as current.

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Amount of investment in marketable security, classified as noncurrent.

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