Business Segments - Additional Information (Details) (USD $)	12 Months Ended				1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended
	May 31, 2013 Segment	May 31, 2012	May 31, 2011	May 31, 2012 Normal Replacement And Upgrades To Sustain Existing Operations Amount Incurred To Acquire Aggregate Reserves	Jul. 31, 2011 Exchange of Productive Assets	May 31, 2011 Exchange of Productive Assets	May 31, 2012 Cement	May 31, 2011 Cement	Apr. 30, 2012 Aggregates	May 31, 2012 Aggregates	May 31, 2012 Consumer Products Exchange of Productive Assets	May 31, 2012 Crestmore Cement Plant	May 31, 2012 Corporate	May 31, 2013 Hunter Cement Plant	May 31, 2012 Hunter Cement Plant	May 31, 2011 Hunter Cement Plant	May 31, 2012 Ready-Mix Concrete	May 31, 2013 Maximum	May 31, 2012 Maximum	May 31, 2011 Maximum	May 31, 2013 Net Sales customer	May 31, 2012 Net Sales customer	May 31, 2011 Net Sales customer
Segment Reporting Information [Line Items]
Number of operating business segments	3
Number of customers exceeding 10% threshold																					0	0	0
Sales percentage represented by major customers																		10.00%	10.00%	10.00%
Segment operating profit												$ 2,500,000
Gain (loss) on disposition of assets	8,900,000	73,100,000	20,900,000		1,600,000	12,000,000	2,500,000	1,700,000	20,800,000		1,600,000
Restructuring charges included in operating profit		2,000,000					1,100,000			400,000			1,200,000				500,000
Capital expenditure incurred for expansion	67,426,000	72,906,000	25,430,000											75,300,000	72,900,000	25,400,000
Capitalized interest paid														38,500,000	32,300,000	11,000,000
Upgrades of existing equipment and acquisitions	$ 25,395,000	$ 33,430,000	$ 20,253,000	$ 18,000,000