Stock Options and Stock Based Compensation - Schedule of Outstanding Stock Options (Detail) - $ / shares
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12 Months Ended |
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May 31, 2018 |
May 31, 2017 |
May 31, 2016 |
May 31, 2015 |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Number of Shares, Outstanding Options |
318,332
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360,000
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147,500
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332,500
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| Weighted Average Exercise Price, Outstanding Options |
$ 2.36
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$ 2.28
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$ 3.11
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$ 3.68
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| Weighted Average Remaining Contractual Life (yrs), Outstanding Options |
6 years 9 months 18 days
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| Exercisable Options, Number of Shares |
282,497
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| Exercisable Options, Weighted Average Exercise Price |
$ 2.44
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| Options 1 [Member] |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Number of Shares, Outstanding Options |
170,832
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| Weighted Average Exercise Price, Outstanding Options |
$ 1.70
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| Weighted Average Remaining Contractual Life (yrs), Outstanding Options |
8 years 6 months
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| Exercisable Options, Number of Shares |
134,997
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| Exercisable Options, Weighted Average Exercise Price |
$ 1.70
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| Options 2 [Member] |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Number of Shares, Outstanding Options |
15,000
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| Weighted Average Exercise Price, Outstanding Options |
$ 2.53
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| Weighted Average Remaining Contractual Life (yrs), Outstanding Options |
5 years 3 months 19 days
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| Exercisable Options, Number of Shares |
15,000
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| Exercisable Options, Weighted Average Exercise Price |
$ 2.53
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| Options 3 [Member] |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Number of Shares, Outstanding Options |
77,500
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| Weighted Average Exercise Price, Outstanding Options |
$ 2.85
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| Weighted Average Remaining Contractual Life (yrs), Outstanding Options |
5 years 10 months 25 days
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| Exercisable Options, Number of Shares |
77,500
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| Exercisable Options, Weighted Average Exercise Price |
$ 2.85
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| Options 4 [Member] |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Number of Shares, Outstanding Options |
55,000
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| Weighted Average Exercise Price, Outstanding Options |
$ 3.65
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| Weighted Average Remaining Contractual Life (yrs), Outstanding Options |
3 years
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| Exercisable Options, Number of Shares |
55,000
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| Exercisable Options, Weighted Average Exercise Price |
$ 3.65
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