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Percentage of employer's matching contributions to a defined contribution plan that vests in a given year.

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Maximum amount the employee may contribute to a defined contribution plan.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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Note 11 - Employee Benefits (Details Textual) - USD ($)			1 Months Ended										5 Months Ended		12 Months Ended
Note 11 - Employee Benefits (Details Textual) - USD ($)	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