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Note 12 - Employee Benefits (Details Textual) - USD ($) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Aug. 31, 2017 | May 31, 2017 | Aug. 31, 2016 | May 31, 2016 | May 31, 2015 | May 31, 2014 | May 31, 2013 | May 31, 2012 | Aug. 31, 2011 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted |  |  |  |  |  |  |  |  |  | 799,110 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized |  |  |  |  |  |  |  |  |  | 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 |  |  |  |  |  |  |  |  |  | $ 1,250,000 | $ 883,000 | $ 1,404,000
Allocated Share-based Compensation Expense, Net of Tax |  |  |  |  |  |  |  |  |  | $ 738,000 | $ 547,000 | $ 870,000
Allocated Share Based Compensation Expense Net Of Tax Amount Per Basic And Diluted Share |  |  |  |  |  |  |  |  |  | $ 0.01 | $ 0.01 | $ 0.02
Income Tax Expense (Benefit) |  |  |  |  |  |  |  |  |  | $ (33,811,000) | $ 23,602,000 | $ 24,946,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number |  |  |  |  |  |  |  |  |  | 918,583 | 922,934 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term |  |  |  |  |  |  |  |  |  | 4 years |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value |  |  |  |  |  |  |  |  |  | $ 7,600,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number |  |  |  |  |  |  |  |  |  | 505,355 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term |  |  |  |  |  |  |  |  |  | 3 years 36 days |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value |  |  |  |  |  |  |  |  |  | $ 5,000,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value |  |  |  |  |  |  |  |  |  | 830,000 | $ 1,900,000 | 2,400,000
Proceeds from Stock Options Exercised |  |  |  |  |  |  |  |  |  | 1,100,000 | 4,400,000 | 3,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value |  |  |  |  |  |  |  |  |  | 515,000 | 534,000 | 502,000
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability |  |  |  |  |  |  |  |  |  | $ (56,500,000) |  |
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 |  |  |  |  |  |  |  |  |  | 2,100,000 | 2,100,000 | 1,900,000
Retirement Savings Plan, Participants Less Than 50 Years Old [Member] |  |  |  |  |  |  |  |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount |  |  |  |  |  |  |  |  |  | 18,000 |  |
Retirement Savings Plan, Participants Over50 Years Old [Member] |  |  |  |  |  |  |  |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount |  |  |  |  |  |  |  |  |  | 24,000 |  |
Accounting Standards Update 2016-09 [Member] |  |  |  |  |  |  |  |  |  |  |  |
Income Tax Expense (Benefit) |  |  |  |  |  |  |  |  |  | $ (176,000) |  |
Performance Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted |  |  |  |  |  |  |  |  | 104,000 |  |  |
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 |  |  |  |  |  |  |  |  |  | $ 484,000 |  |
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 |  | 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 | 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 |  |  |  |  |  |  |  |  |  | $ 1,300,000 |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition |  |  |  |  |  |  |  |  |  | 3 years 36 days |  |
Unvested Performance Unit Awards [Member] |  |  |  |  |  |  |  |  |  |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized |  |  |  |  |  |  |  |  |  | $ 3,900,000 |  |
Service Based Options [Member] |  |  |  |  |  |  |  |  |  |  |  |
Stock Granted, Value, Share-based Compensation, Gross |  |  |  |  |  |  |  |  |  | $ 592,000 | $ 227,000 | $ 918,000
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 |  |  |  |  |  |  |  |  |  | 445,172 |  |
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 |  |  |  |  |  |  |  |  |  | 306,383 |  |
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 |  |  |  |  |  |  |  |  |  | 473,411 |  |
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 |  |  |  |  |  |  |  |  |  | 64,600 |  |
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 Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Net number of non-option equity instruments granted to participants. + 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)(iv)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + 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 (a)(3) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding. + 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=96867065&loc=d3e5070-113901 + Details
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- Definition Number of options outstanding, including both vested and non-vested options. + 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=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition 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. + 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 (a)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition 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. + 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=96867065&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=96867065&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=96867065&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/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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