Business Segments - Additional Information (Detail) (USD $)	3 Months Ended
	Aug. 31, 2013 Segment	Aug. 31, 2012
Segment Reporting Information [Line Items]
Number of operating business segments	3
Capital expenditure incurred for expansion	$ 7,125,000	$ 28,114,000
Upgrades of existing equipment and acquisitions	5,373,000	4,496,000
Hunter Cement Plant
Segment Reporting Information [Line Items]
Capital expenditure incurred for expansion	7,000,000	28,100,000
Capitalized interest paid		18,400,000
Upgrades of existing equipment and acquisitions		$ 4,206,000
Maximum
Segment Reporting Information [Line Items]
Sales percentage represented by major customers	10.00%	10.00%
Net Sales
Segment Reporting Information [Line Items]
Number of customers exceeding 10% threshold	0	0