Note 13 - Employee Stock Option and Retirement Plans (Details Textual) - USD ($) | Jan. 12, 2018 | Dec. 19, 2017 | Jan. 13, 2017 | Jun. 30, 2017 | Jan. 31, 2017 | May 31, 2018 | Feb. 28, 2018 | Nov. 30, 2017 | May 31, 2017 | Feb. 28, 2017 | Nov. 30, 2016 | Feb. 28, 2015 | May 31, 2018 | May 31, 2017 | Aug. 31, 2017 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | | | | | | 0 | | | | | | | | | | |
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price | [1] | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance | | | | | | | 3,279,000 | 3,402,000 | | 3,669,000 | | | | | 3,279,000 | | 3,366,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance | | | | | | | $ 151.79 | $ 151.15 | | $ 149.09 | | | | | $ 151.79 | | $ 139.29 |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total | | | | | | | $ 78,300,000 | | | | | | | | $ 78,300,000 | | |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition | | | | | | | | | | | | | | | 3 years 73 days | | |
Share Price | | | | | | | $ 201.01 | | | | | | | | $ 201.01 | | $ 157.18 |
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent | | | 85.00% | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate | | | 10.00% | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Contribution Limit | | | $ 25,000 | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, Employee Stock Purchase Plans | | | | | | | 16,312 | | | | 17,314 | | | | 50,706 | 54,554 | |
Treasury Stock Acquired, Average Cost Per Share | | | | | | | $ 170.86 | | | | $ 140.84 | | | | $ 156.88 | $ 137.38 | |
Common Stock, Capital Shares Reserved for Future Issuance | | | | | | | 282,466 | | | | | | | | 282,466 | | |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent | | | | | | | | | | | | | | | 60.00% | | |
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay | | | | | | | | | | | | | | | 4.00% | | |
Defined Contribution Plan, Employer Matching Contribution, Vesting Period | | | | | | | | | | | | | | | 5 years | | |
Defined Contribution Plan, Employer Discretionary Contribution Amount | | | | | | | | | | | | | | | $ 8,500,000 | $ 7,300,000 | |
Maximum [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price | | | | | | | | | | | $ 163.05 | | | | $ 190.04 | $ 154.01 | |
Employee Stock Option [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price | | | | | | | | | | | | $ 169.16 | $ 152.51 | | | | |
Performance Shares [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | | | | | | | | | | | 61,744 | 22,460 | | | | |
Performance Shares [Member] | Code Red, Inc. [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | | | | | | | | | | | | | | 4 years | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | | | | | | | | | | | | | 68,761 | | | |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total | | | | | | | $ 200,000 | | | | | | | | $ 200,000 | | |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition | | | | | | | | | | | | | | | 255 days | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | | | | | | | | | | | | 40.00% | | | |
Performance Shares [Member] | Vermilion Holdings Limited [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | | | | | 61,744 | | | | | | | | | | | |
Performance Shares [Member] | Vermilion Holdings Limited [Member] | Share-based Compensation Award, Tranche One [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | | | | 40.00% | | | | | | | | | 0.00% | | |
Performance Shares [Member] | Vermilion Holdings Limited [Member] | Share-based Compensation Award, Tranche Two [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | | | | 20.00% | | | | | | | | | 100.00% | | |
Performance Shares [Member] | BI-SAM Technologies [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | | | | 206,417 | | | | | | | | | | | | |
Performance Shares [Member] | BI-SAM Technologies [Member] | Share-based Compensation Award, Tranche One [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | | | 40.00% | | | | | | | | | | 0.00% | | |
Performance Shares [Member] | BI-SAM Technologies [Member] | Share-based Compensation Award, Tranche Two [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | | | 20.00% | | | | | | | | | | 80.00% | | |
Restricted Stock [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | | | | | | | | 1,000 | | | | | 961 | 12,927 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | | | | | | | | | | $ 182.17 | | | | | $ 182.17 | $ 157.50 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance | | | | | | | 154,000 | 155,000 | | 162,000 | | | | | 154,000 | | 182,000 |
LTIP [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized | | | 5,750,000 | | | | | 5,750,000 | [2],[3] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | | | | | | | $ 5,200,000 | | | | $ 4,300,000 | | | | $ 40,300,000 | $ 34,800,000 | |
LTIP [Member] | Employee Stock Option [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | | | 5 years | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | | | | | | | | | | | | | | 569,305 | | |
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price | | | | | | | | | | | | | | | $ 190.04 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance | | | | | | | 3,279,096 | | | | | | | | 3,279,096 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance | | | | | | | $ 151.79 | | | | | | | | $ 151.79 | | |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total | | | | | | | $ 65,000,000 | | | | | | | | $ 65,000,000 | | |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition | | | | | | | | | | | | | | | 3 years 109 days | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number | | | | | | | 1,100,000 | | | | | | | | 1,100,000 | | 900,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price | | | | | | | $ 124.52 | | | | | | | | $ 124.52 | | $ 105.14 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | | | | | | | $ 84,100,000 | | | | | | | | $ 84,100,000 | | $ 49,700,000 |
LTIP [Member] | Employee Stock Option [Member] | Maximum [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period | | | 10 years | | | | | | | | | | | | | | |
LTIP [Member] | Restricted Stock [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | | | | | | | | | | | | | | | 5 years | | |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total | | | | | | | $ 13,300,000 | | | | | | | | $ 13,300,000 | | |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition | | | | | | | | | | | | | | | 3 years | | |
Share Price | | | | | | | $ 201.01 | | | | | | | | $ 201.01 | | $ 157.18 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | | | | | | | | | | | | | 961 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | | | | | | | | | | | | | | | $ 182.17 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance | | | | | | | 153,842 | | | | | | | | 153,842 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Nonvested | | | | | | | $ 30,900,000 | | | | | | | | $ 30,900,000 | | $ 28,600,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Pre-Tax Intrinsic Value | | | | | | | | | | | | | | | $ 2,800,000 | $ 15,600,000 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Share Equivalent | | | | | | | | | | | 2.5 | | | | | 2.5 | |
LTIP [Member] | Restricted Stock [Member] | Maximum [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Pre-Tax Intrinsic Value | | | | | | | $ 100,000 | | | | $ 100,000 | | | | | | |
Director Plan [Member] | | | | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized | | | 250,000 | | | | | 250,000 | [2],[3] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | 18,963 | | 23,846 | | | | 19,000 | | | | | | | | | |
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price | | | | | | | | $ 197.75 | | | | | | | | | |
Common Stock, Capital Shares Reserved for Future Issuance | | | 250,000 | | | | | | | | | | | | | | |
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[1] | There were no employee stock options granted during the three months ended May 31, 2018. | |
[2] | On December 19, 2017, the Company's stockholders approved the LTIP. As part of the approval, an additional 5,750,000 shares of common stock were added to the LTIP's share reserve. | |
[3] | On December 19, 2017, the Company's stockholders approved the amended and restated 2008 Non-Employee Director' Stock Option Plan, which was renamed the Non-Employee Directors' Stock Option and Award Plan, as Amended and Restated (the "Director Plan"). As part of the approval, an additional 250,000 shares of commons stock were added to the Director Plan share reserve. | |