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Note 11 - Employee Benefits (Details Textual) - USD ($) |  |  | 1 Months Ended | 5 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Aug. 13, 2020 | May 07, 2019 | May 31, 2022 | May 31, 2021 | May 31, 2020 | May 31, 2019 | Dec. 31, 2018 | Aug. 31, 2018 | May 31, 2018 | Aug. 31, 2017 | May 31, 2017 | May 31, 2015 | Dec. 31, 2022 | May 31, 2015 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Granted |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,509,687 |  |
Common Stock, Par or Stated Value Per Share |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.01 |  | $ 0.01 | $ 0.01 |
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Forfeiture Rate Of Unvested Outstanding Awards |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.25% |  |
Share-Based Payment Arrangement, Expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,814,000 | $ 2,518,000 | $ 1,851,000
Share-Based Payment Arrangement, Expense, after Tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,200,000 | $ 1,900,000 | $ 1,400,000
Allocated Share Based Compensation Expense Net Of Tax Amount Per Basic And Diluted Share |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.03 | $ 0.02 | $ 0.02
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number, Ending Balance |  |  |  |  |  |  |  |  |  |  |  |  | 915,391 |  | 915,391 | 1,029,466 |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 years 6 months |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Intrinsic Value |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,900,000 |  | $ 3,900,000 |  |
Exercisable, shares (in shares) |  |  |  |  |  |  |  |  |  |  |  |  | 371,241 |  | 371,241 |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term (Year) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 years |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Intrinsic Value |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,400,000 |  | $ 2,400,000 |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period, Intrinsic Value |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000.0 | $ 789,000 | $ 4,100,000
Proceeds from Stock Options Exercised |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,000,000.0 | 1,700,000 | 4,800,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested in Period, Fair Value |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 691,000 | 411,000 | 539,000
Defined Contribution Plan, Employer Matching Contribution, Percent of Match |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 35.00% |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.00% |  |
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20.00% |  |
Defined Contribution Plan, Cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,000,000.0 | 3,000,000.0 | 3,000,000.0
Retirement Savings Plan, Participants Less Than 50 Years Old [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,500 |  |
Retirement Savings Plan, Participants Over50 Years Old [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 27,000 |  |
Stock Split [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Par or Stated Value Per Share | $ 0.01 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note, Stock Split, Dividend Settlement, Percent | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-Based Payment Arrangement, Option [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding |  |  |  |  |  |  |  |  |  |  |  |  | 10,313 |  | 10,313 |  |
Performance Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding |  |  |  |  |  |  |  |  |  |  |  |  | 905,078 |  | 905,078 |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,000,000.0 |  |
Performance Shares [Member] | Awards Paid to Employees Upon Vesting [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Granted |  |  | 102,900 | 98,400 | 73,205 | 45,000 | 3,000 | 3,000 | 42,000 | 3,000 | 65,013 |  | 21,000 | 32,513 |  |  |
Performance Shares [Member] | One Half of Awards Paid Immediately Upon Vesting and One Half Credited to Employees' Accounts [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Granted |  |  |  |  |  | 60,000 |  |  | 68,550 |  |  |  |  |  |  |  |
Unvested Service Based Option Awards [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,300,000 |  | $ 2,300,000 |  |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 years 6 months |  |
Unvested Performance Unit Awards [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,200,000 |  | $ 2,200,000 |  |
Service Based Options [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares Granted, Value, Share-Based Payment Arrangement, before Forfeiture |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 819,000 | $ 1,800,000 | $ 160,000
2015 Equity Incentive Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized |  | 1,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2015 Equity Incentive Plan [Member] | Stock Split [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized | 3,950,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2015 Equity Incentive Plan [Member] | Share-Based Payment Arrangement, Option [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Annual Percentage Of Award Which Vests |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20.00% |  |
2015 Equity Incentive Plan [Member] | Full Value Awards [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized |  | 558,334 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2015 Equity Incentive Plan [Member] | Performance Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Granted |  |  |  |  |  |  |  |  |  |  |  | 86,505 |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding |  |  |  |  |  |  |  |  |  |  |  |  | 226,361 |  | 226,361 |  |
Minimum [Member] | 2015 Equity Incentive Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7 years |  |
Maximum [Member] | 2015 Equity Incentive Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 years |  |

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- Definition Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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- Definition Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(1) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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- Definition Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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