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Summary of Significant Accounting Policies and Practices - Additional Information (Detail)
 3 Months Ended
Aug. 31, 2015
USD ($)
Segment
Location
Customer
shares
Aug. 31, 2014
shares
May. 31, 2015
USD ($)
Nov. 30, 2010
Significant Accounting Policies [Line Items]        
Number of operating segments | Segment 3      
Number of locations in which company operates | Location 150      
Goodwill $ 262,194,000   $ 107,773,000  
Number of shares estimated to be issued to acquire non-controlling interests | shares 728,266      
Cash payment to acquire non controlling interest $ 5,900,000      
Deferred tax assets recovery from future taxable income percentage 50.00%      
Workers compensation our self-insured retention $ 1,000,000      
Automobile liability self-insured retention 500,000      
General liability claims we have an effective self-insured retention 3,000,000      
Medical claims, our self-insured retention 175,000      
Environmental liability claims, our self-insured retention 500,000      
Amount of earned but unbilled revenue included in accounts receivable $ 29,700,000   $ 18,400,000  
Options to purchase shares of common stock excluded from the computation of diluted earnings per share | shares 0 0    
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]        
Significant Accounting Policies [Line Items]        
Number of customers accounted for more than specified percentage of consolidated revenues | Customer 0      
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Minimum [Member]        
Significant Accounting Policies [Line Items]        
Percentage of consolidated revenues 10.00%      
Quest Integrity [Member]        
Significant Accounting Policies [Line Items]        
Purchase percentage of quest       95.00%