Business Segments - Additional Information (Detail) (USD $)	6 Months Ended
	Nov. 30, 2013 Segment	Nov. 30, 2012
Segment Reporting Information [Line Items]
Number of operating business segments	3
Capital expenditure incurred for expansion	$ 7,125,000	$ 36,118,000
Upgrades of existing equipment and acquisitions	17,295,000	10,845,000
Hunter Cement Plant
Segment Reporting Information [Line Items]
Capital expenditure incurred for expansion	7,000,000	36,100,000
Capitalized interest paid		$ 18,400,000
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