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Note 13 - Employee Benefits (Details Textual) - USD ($) | 1 Months Ended | 12 Months Ended
--- | --- | ---
May. 31, 2015 | May. 31, 2014 | May. 31, 2013 | May. 31, 2012 | Aug. 31, 2011 | Aug. 31, 2010 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
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 |  |
Two Thousand and Fifteen Plan [Member] | Employee Stock Option [Member] |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period |  |  |  |  |  |  | 1 year |  |
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 |  |  |  |  |  |  | 153,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number |  |  |  |  |  |  | 850,184 |  |
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 |  |  |  |  |  |  | 54,500 |  |
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 |  |  |  |  |  |  | 137,474 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number |  |  |  |  |  |  | 697,184 |  |
Employee Stock Option [Member] | Awards Paid to Employees Upon Vesting [Member] |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted | 19,500 | 11,000 |  |  |  |  |  |  |
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 | 35,000 | 36,400 | 62,550 | 59,250 | 62,400 |  |  |  |
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 Award, Non-Option Equity Instruments, Granted |  |  |  |  |  | 95,100 |  |  |
Sharebased Compensation Arrangement By Share Based Payment Awards Annual Service Vesting Percentage |  |  |  |  |  | 5.00% |  |  |
Average Annual Earnings Percentage Increase Goal Of Share Based Compensation Awards |  |  |  |  |  | 15.00% |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value |  |  |  |  |  |  | $ 737,000 |  |
Unvested Service Based Option Awards [Member] |  |  |  |  |  |  |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized |  |  |  |  |  |  | $ 1,700,000 |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition |  |  |  |  |  |  | 3 years 146 days |  |
Unvested Performance Unit Awards [Member] |  |  |  |  |  |  |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized |  |  |  |  |  |  | $ 2,400,000 |  |
Service Based Options [Member] |  |  |  |  |  |  |  |  |
Stock Granted, Value, Share-based Compensation, Gross |  |  |  |  |  |  | 918,000 | $ 475,000 | $ 953,000
Participants Less Than50 Years Old [Member] |  |  |  |  |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount |  |  |  |  |  |  | 18,000 |  |
Participants Over50 Years Old [Member] |  |  |  |  |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount |  |  |  |  |  |  | 24,000 |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount |  |  |  |  |  |  | $ 0 | $ 0 | 0
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | 800,000 |  |  |  |  |  | 800,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number |  |  |  |  |  |  | 850,184 | 977,867 |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted | 212,500 |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  | $ 1,404,000 | $ 921,000 | 1,084,000
Allocated Share-based Compensation Expense, Net of Tax |  |  |  |  |  |  | $ 870,000 | $ 571,000 | $ 672,000
Allocated Share Based Compensation Expense Net Of Tax Amount Per Basic And Diluted Share |  |  |  |  |  |  | $ 0.03 | $ 0.02 | $ 0.02
Excess Tax Benefit from Share-based Compensation, Financing Activities |  |  |  |  |  |  | $ 432,000 | $ 115,000 | $ 165,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term |  |  |  |  |  |  | 3 years 219 days |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value |  |  |  |  |  |  | $ 2,000,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number |  |  |  |  |  |  | 512,634 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term |  |  |  |  |  |  | 2 years 182 days |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value |  |  |  |  |  |  | $ 1,700,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value |  |  |  |  |  |  | 2,400,000 | 761,000 | 915,000
Proceeds from Stock Options Exercised |  |  |  |  |  |  | 3,500,000 | 1,200,000 | 1,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value |  |  |  |  |  |  | $ 502,000 | 541,000 | 636,000
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 Recognized |  |  |  |  |  |  | $ 1,900,000 | $ 1,500,000 | $ 1,400,000

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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://www.xbrl.org/2003/role/presentationRef -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=6415400&loc=d3e5070-113901 + Details
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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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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