Defined Contribution Benefit Plan - Additional Information (Detail) (USD $)
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12 Months Ended | ||
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May 31, 2013
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May 31, 2012
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May 31, 2011
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Defined Benefit Plan Disclosure [Line Items] | |||
Defined contribution 401(K) benefit expense | $ 863,000 | $ 760,000 | $ 733,000 |
First 3% employees deferred amount
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Defined Benefit Plan Disclosure [Line Items] | |||
Defined contribution plan employer matching contribution | 100.00% | ||
Next 2% employees deferred amount
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Defined Benefit Plan Disclosure [Line Items] | |||
Defined contribution plan employer matching contribution | 50.00% |