Business Segments - Additional Information (Detail) (USD $)	12 Months Ended																12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010	May 31, 2012 Consumer Products	May 31, 2012 Exchange of Productive Assets	Jul. 31, 2011 Exchange of Productive Assets	May 31, 2011 Exchange of Productive Assets	May 31, 2012 Crestmore Cement Plant	May 31, 2011 Crestmore Cement Plant	May 31, 2010 Crestmore Cement Plant	May 31, 2012 Other Segment	May 31, 2011 Other Segment	May 31, 2012 Hunter Cement Plant	May 31, 2011 Hunter Cement Plant	May 31, 2010 Hunter Cement Plant	May 31, 2012 Amount Incurred To Acquire Aggregate Reserves	May 31, 2012 Maximum	May 31, 2011 Maximum	May 31, 2010 Maximum
Segment Reporting Information [Line Items]
Sales percentage represented by major customers																	10.00%	10.00%	10.00%
Segment operating profit	$ 70,100,000	$ 15,400,000	$ 4,800,000	$ 30,900,000				$ 2,500,000	$ 1,700,000	$ 3,400,000	$ 20,800,000	$ 12,000,000
Gain Loss On Disposition Of Assets					10,500,000	1,600,000	12,000,000
Capital expenditure incurred for expansion	72,906,000	25,430,000	5,337,000										72,900,000	25,400,000	5,300,000
Capitalized interest paid													32,300,000	11,000,000
Upgrades of existing equipment and acquisitions	33,430,000	20,253,000	8,322,000
Aggregate reserves																$ 18,000,000