Summary of Significant Accounting Policies and Practices - Additional Information (Detail) (USD $)	3 Months Ended
	Aug. 31, 2013	Aug. 31, 2012	Jul. 01, 2013	May 31, 2013
Significant Accounting Policies [Line Items]
Excess of Market capitalization over carrying value of net assets			$ 500,000,000
Excess of Market capitalization over carrying value of net assets, percentage			170.00%
Goodwill	108,977,000			103,466,000
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	$ 26,795,000			$ 25,516,000
Single customer accounts consolidated revenue	10.00%
Options to purchase shares of common stock outstanding	0	557,000