Note 5 - Fair Value Measurements - Fair Value by Major Security Type (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021
Short-term marketable securities	$ 5,270	$ 5,686
Long-term Securities	2,004	1,875
Fair Value, Nonrecurring [Member]
Cost Basis	8,539	8,493
Unrealized Gains (Losses)	(81)	0
Fair Value	8,458	8,493
Cash Equivalents	1,184	932
Short-term marketable securities	5,270	5,686
Long-term Securities	2,004	1,875
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Cost Basis	1,184	932
Unrealized Gains (Losses)	0	0
Fair Value	1,184	932
Cash Equivalents	1,184	932
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Cost Basis	7,355	7,561
Unrealized Gains (Losses)	(81)	0
Fair Value	7,274	7,561
Cash Equivalents	0	0
Short-term marketable securities	5,270	5,686
Long-term Securities	2,004	1,875
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Certificates of Deposit [Member]
Cost Basis	1,025	1,494
Unrealized Gains (Losses)	0	0
Fair Value	1,025	1,494
Cash Equivalents	0	0
Short-term marketable securities	723	694
Long-term Securities	302	800
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| US States and Political Subdivisions Debt Securities [Member]
Cost Basis	5,413	5,139
Unrealized Gains (Losses)	(56)	(1)
Fair Value	5,357	5,138
Cash Equivalents	0	0
Short-term marketable securities	3,906	4,205
Long-term Securities	1,451	933
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Cost Basis	917	928
Unrealized Gains (Losses)	(25)	1
Fair Value	892	929
Cash Equivalents	0	0
Short-term marketable securities	641	787
Long-term Securities	$ 251	$ 142

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before tax, of unrealized gain (loss) in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

No definition available.

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleAccumulatedGrossUnrealizedGainLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of investment in marketable security, classified as current.

+ References

No definition available.

+ Details

Name:	us-gaap_MarketableSecuritiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in marketable security, classified as noncurrent.

+ References

No definition available.

+ Details

Name:	us-gaap_MarketableSecuritiesNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: