Customer Concentration - Additional Information (Detail) - USD ($)	12 Months Ended
May 31, 2017	May 31, 2016
Revenue, Major Customer [Line Items]
Net sales	$ 236,504,000	$ 211,774,000
Sun Home Services, Inc [Member]
Revenue, Major Customer [Line Items]
Net sales		$ 22,231,000
Net sale Percentage	10.00%	10.00%
Customer concentration risk percentage description	During fiscal 2017, no individual customer had net sales exceeding 10 percent of total net sales. During fiscal 2016, net sales to Sun Home Services, Inc. ("Sun Home") totaled $22,231,000 or 10 percent of total net sales. Based on past sales to Sun Home, the Corporation could have a material adverse effect on its financial condition and results of operations if the Corporation experienced a loss of this customer or if the volume of sales significantly decreased.

Revenue, Major Customer [Line Items]

$ 22,231,000

Customer concentration risk percentage description

During fiscal 2017, no individual customer had net sales exceeding 10 percent of total net sales. During fiscal 2016, net sales to Sun Home Services, Inc. ("Sun Home") totaled $22,231,000 or 10 percent of total net sales. Based on past sales to Sun Home, the Corporation could have a material adverse effect on its financial condition and results of operations if the Corporation experienced a loss of this customer or if the volume of sales significantly decreased.