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Defined Contribution Benefit Plan - Additional Information (Detail) - USD ($) | 12 Months Ended
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May 31, 2018 | May 31, 2017 | May 31, 2016
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution 401(K) benefit expense | $ 1,325,000 | $ 1,259,000 | $ 1,188,000
First 3% employees deferred amount |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan employer matching contribution | 100.00% |  |
Next 2% employees deferred amount |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan employer matching contribution | 50.00% |  |

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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- Details
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- Details
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