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Share based compensation arrangement by share based payment award fair value assumptions expected forfeiture rate of unvested outstanding awards.

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Share based compensation arrangement by share based payment award number of shares reserved for issuance under awards outstanding.

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The percentage of annual service vesting of share-based compensation awards.

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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.

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The amount of expense, net of income tax, 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.

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Amount of cost for defined contribution plan.

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Amount of discretionary contributions made by an employer to a defined contribution plan.

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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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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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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of income tax expense (benefit) from continuing operations attributable to an adjustment of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, 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 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.

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Net number of non-option equity instruments granted to participants.

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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).

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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 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.

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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 forfeitures, of stock or other type of equity granted of any equity-based compensation plan other than an employee stock ownership plan (ESOP).

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