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Face amount or stated value per share of common stock.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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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.

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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.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Value, before forfeiture, of shares granted under share-based payment arrangement. Excludes employee stock ownership plan (ESOP).

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Note 12 - Employee Benefits (Details Textual)				1 Months Ended											5 Months Ended	12 Months Ended
Note 12 - Employee Benefits (Details Textual)	Aug. 13, 2020 $ / shares shares	May 07, 2019 shares	May 01, 2015	May 31, 2021 shares	May 31, 2020 shares	May 31, 2019 shares	Dec. 31, 2018 shares	Aug. 31, 2018 shares	May 31, 2018 shares	Aug. 31, 2017 shares	May 31, 2017 shares	Aug. 31, 2016 shares	May 31, 2016 shares	May 31, 2015 shares	May 31, 2015 shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted (in shares) \| shares																2,345,554
Common Stock, Par or Stated Value Per Share (in dollars per share) \| $ / shares																$ 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																$ 2,518,000	$ 1,851,000	$ 1,817,000
Share-based Payment Arrangement, Expense, after Tax																$ 1,900,000	$ 1,400,000	$ 1,400,000
Allocated Share Based Compensation Expense Net Of Tax Amount Per Basic And Diluted Share (in dollars per share) \| $ / shares																$ 0.02	$ 0.02	$ 0.02
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares) \| shares																1,029,466	711,780
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)																4 years 7 months 6 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value																$ 3,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number (in shares) \| shares																398,415
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term (Year)																2 years 8 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value																$ 2,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value																789,000	$ 4,100,000	$ 1,400,000
Proceeds from Stock Options Exercised																874,000	4,800,000	1,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value																$ 411,000	539,000	569,000
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, Employer Discretionary Contribution Amount																$ 0	0	0
Defined Contribution Plan, Cost																3,000,000.0	3,000,000.0	2,700,000
Retirement Savings Plan, Participants Less Than 50 Years Old [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount																19,500
Retirement Savings Plan, Participants Over50 Years Old [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount																$ 26,000
Stock Split To [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	3
Common Stock, Par or Stated Value Per Share (in dollars per share) \| $ / shares	$ 0.01
Stockholders' Equity Note, Stock Split, Dividend Settlement, Percent	50.00%
Stock Split from [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	2
Share-based Payment Arrangement, Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding (in shares) \| shares																51,565
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)			5 years													5 years
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding (in shares) \| shares																977,901
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value																$ 1,700,000
Performance Shares [Member] \| Awards Paid to Employees Upon Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted (in shares) \| shares				98,400	73,205	45,000	3,000	3,000	42,000	3,000	65,013	2,501	32,513		48,750
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 (in shares) \| shares						60,000			68,550		163,754		86,505
Share-based Compensation Arrangement By Share-based Payment Awards, Annual Service Vesting Percentage											10.00%
Unvested Service Based Option Awards [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total																$ 2,400,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)																3 years 10 months 24 days
Unvested Performance Unit Awards [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total																$ 2,100,000
Service Based Options [Member]
Shares Granted, Value, Share-based Payment Arrangement, before Forfeiture																$ 1,800,000	$ 160,000	$ 401,000
2015 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted (in shares) \| shares														87,503
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares) \| shares		1,300,000
2015 Equity Incentive Plan [Member] \| Stock Split To [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares) \| shares	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] \| Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding (in shares) \| shares																322,529
2015 Equity Incentive Plan [Member] \| Full Value Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares) \| shares		558,334
The 2005 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares) \| shares																0
The 2005 Stock Incentive Plan [Member] \| Share-based Payment Arrangement, Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding (in shares) \| shares																0
Minimum [Member] \| 2015 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)																7 years
Maximum [Member] \| 2015 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)																10 years