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Note 14 - Employee Benefits (Details Textual) - USD ($) | 1 Months Ended | 12 Months Ended | 37 Months Ended
--- | --- | --- | ---
Dec. 31, 2018 | Aug. 31, 2018 | May 31, 2018 | Aug. 31, 2017 | May 31, 2017 | Aug. 31, 2016 | May 31, 2016 | May 31, 2015 | May 31, 2014 | May 31, 2013 | May 31, 2012 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | May 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted |  |  |  |  |  |  |  |  |  |  |  | 998,022 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | 1,333,333 |  |  |  |  |  |  |  |  |  |  | 1,333,333 |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Forfeiture Rate Of Unvested Outstanding Awards |  |  |  |  |  |  |  |  |  |  |  | 1.25% |  |  |
Allocated Share-based Compensation Expense, Total |  |  |  |  |  |  |  |  |  |  |  | $ 3,323,000 | $ 1,250,000 | $ 883,000 |
Allocated Share-based Compensation Expense, Net of Tax |  |  |  |  |  |  |  |  |  |  |  | $ 2,600,000 | $ 738,000 | $ 547,000 |
Allocated Share Based Compensation Expense Net Of Tax Amount Per Basic And Diluted Share |  |  |  |  |  |  |  |  |  |  |  | $ 0.05 | $ 0.01 | $ 0.01 |
Income Tax Expense (Benefit), Total |  |  |  |  |  |  |  |  |  |  |  | $ 16,002,000 | $ (33,811,000) | $ 23,602,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance | 939,193 |  |  |  |  |  |  |  |  |  |  | 939,193 | 918,583 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term |  |  |  |  |  |  |  |  |  |  |  | 3 years 292 days |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | $ 3,000,000 |  |  |  |  |  |  |  |  |  |  | $ 3,000,000 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number | 545,713 |  |  |  |  |  |  |  |  |  |  | 545,713 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term |  |  |  |  |  |  |  |  |  |  |  | 2 years 255 days |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | $ 2,600,000 |  |  |  |  |  |  |  |  |  |  | $ 2,600,000 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value |  |  |  |  |  |  |  |  |  |  |  | 1,500,000 | $ 830,000 | 1,900,000 |
Proceeds from Stock Options Exercised |  |  |  |  |  |  |  |  |  |  |  | 938,000 | 1,100,000 | 4,400,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value |  |  |  |  |  |  |  |  |  |  |  | $ 547,000 | 515,000 | $ 534,000 |
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability |  |  |  |  |  |  |  |  |  |  |  |  | $ (56,500,000) |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  |  |  |  |  |  |  |  | 21.00% | 35.00% | 35.00% |
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 |  |  |  |  |  |  |  |  |  |  |  | 2,300,000 | 2,100,000 | 2,100,000 |
Retirement Savings Plan, Participants Less Than 50 Years Old [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount |  |  |  |  |  |  |  |  |  |  |  | 18,500 |  |  |
Retirement Savings Plan, Participants Over50 Years Old [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount |  |  |  |  |  |  |  |  |  |  |  | 24,500 |  |  |
Accounting Standards Update 2016-09 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Tax Expense (Benefit), Total |  |  |  |  |  |  |  |  |  |  |  | $ 319,000 | 176,000 |  |
Performance Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  | 5 years
Share-based Compensation Arrangement By Share-based Payment Awards, Annual Service Vesting Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5.00%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value |  |  |  |  |  |  |  |  |  |  |  | $ 2,700,000 |  |  |
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 |  |  | 45,700 |  | 109,169 |  | 57,669 | 58,335 | 60,668 | 104,250 | 98,750 |  |  |  |
Share-based Compensation Arrangement By Share-based Payment Awards, Annual Service Vesting Percentage |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |
Performance Shares [Member] | Awards Paid to Employees Upon Vesting [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted | 2,000 | 2,000 | 28,000 | 2,000 | 43,342 | 1,667 | 21,671 | 32,500 | 18,337 |  |  |  |  |  |
Unvested Service Based Option Awards [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total | $ 1,600,000 |  |  |  |  |  |  |  |  |  |  | $ 1,600,000 |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition |  |  |  |  |  |  |  |  |  |  |  | 3 years 73 days |  |  |
Unvested Performance Unit Awards [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total | $ 2,400,000 |  |  |  |  |  |  |  |  |  |  | $ 2,400,000 |  |  |
Service Based Options [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Granted, Value, Share-based Compensation, Gross |  |  |  |  |  |  |  |  |  |  |  | $ 957,000 | $ 592,000 | $ 227,000 |
Two Thousand and Fifteen Plan [Member] | Employee Stock Option [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Annual Percentage Of Award Which Vests |  |  |  |  |  |  |  |  |  |  |  | 20.00% |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding | 568,873 |  |  |  |  |  |  |  |  |  |  | 568,873 |  |  |
Two Thousand and Fifteen Plan [Member] | Performance Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding | 349,814 |  |  |  |  |  |  |  |  |  |  | 349,814 |  |  |
Two Thousand And Five Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | 0 |  |  |  |  |  |  |  |  |  |  | 0 |  |  |
Two Thousand And Five Plan [Member] | Employee Stock Option [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding | 370,320 |  |  |  |  |  |  |  |  |  |  | 370,320 |  |  |
Two Thousand And Five Plan [Member] | Performance Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Reserved For Issuance Under Awards Outstanding | 0 |  |  |  |  |  |  |  |  |  |  | 0 |  |  |
Minimum [Member] | Two Thousand and Fifteen Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period |  |  |  |  |  |  |  |  |  |  |  | 7 years |  |  |
Maximum [Member] | Two Thousand and Fifteen Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period |  |  |  |  |  |  |  |  |  |  |  | 10 years |  |  |

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- Definition Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. + 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 (d)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Net number of non-option equity instruments granted to participants. + 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 (c)(1)(iv)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + 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 http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition 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. + 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 (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + 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 (d)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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