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Stock Purchase - Additional Information (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
9 Months Ended
Feb. 28, 2015
Dec. 31, 2008
Stock Repurchase Program [Line Items]    
Shares authorized to purchase   1,125,000us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased
Cumulative number of shares repurchased 112,026us-gaap_StockRepurchasedDuringPeriodShares  
Cost of repurchased shares, including commissions $ 923us-gaap_StockRepurchasedDuringPeriodValue