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Note 11 - Stock-based Compensation (Details Textual) - USD ($) $ in Millions							9 Months Ended	12 Months Ended							24 Months Ended	36 Months Ended
	Nov. 25, 2022	Jun. 09, 2022	May 26, 2022	May 27, 2021	Jun. 01, 2020	May 23, 2019	May 31, 2021	May 31, 2023	Dec. 31, 2022	May 31, 2022	Dec. 31, 2021	May 31, 2021	Dec. 31, 2020	May 31, 2020	Aug. 27, 2022	Dec. 31, 2016
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)									66,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)									0		0		0
Stock Issued During Period, Shares, Issued for Services (in shares)									11,166		10,489		17,716
Noninterest Expense [Member]
Share-based Payment Arrangement, Expense									$ 3.4		$ 3.8		$ 2.3
Director [Member]
Stock Issued During Period, Shares, Issued for Services (in shares)			10,300	10,500	16,000	12,000
Share-based Payment Arrangement, Expense										$ 0.3		$ 0.3		$ 0.4
Director [Member] | Forecast [Member]
Share-based Payment Arrangement, Expense								$ 0.3
Corporate and Bank Board Members [Member]
Stock Issued During Period, Shares, Issued for Services (in shares)															1,700
Bank Board Members [Member]
Stock Issued During Period, Shares, Issued for Services (in shares)	300	600
Share-based Payment Arrangement, Expense							$ 0.1
Bank Board Members [Member] | Forecast [Member]
Share-based Payment Arrangement, Expense								$ 0.1
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)									3 years
Share-Based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)																2 years
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent																110.00%
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)																7 years
Performance Shares [Member] | Executive Officer [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)									26,112		22,703		31,295
Performance Shares [Member] | Executive Officer [Member] | The 2021 Award [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)									11,350
Performance Shares [Member] | Executive Officer [Member] | The 2020 Awards [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)									2,778		11,454
Performance Shares [Member] | Executive Officer [Member] | The 2019 Awards [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)									690		23,053
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (in shares)													13,709
Performance Shares [Member] | Executive Officer [Member] | The 2018 Awards [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)											22,836
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (in shares)													14,681

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
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