Summary Of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended				12 Months Ended								1 Months Ended	12 Months Ended																1 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010	Apr. 30, 2012	May 31, 2012 Paid	May 31, 2012 Co-venturer	May 31, 2012 Real Estate	May 31, 2011 Real Estate	May 31, 2010 Real Estate	May 31, 2012 Cement	May 31, 2011 Cement	May 31, 2010 Cement	Apr. 30, 2012 Aggregates	May 31, 2012 All Other	May 31, 2012 Additional	May 31, 2012 Ready-Mix Concrete	Jul. 31, 2011 Ready-Mix Concrete Property	May 31, 2012 Stone, Sand And Gravel	Jul. 31, 2011 Nonoperating Development Properties Property	May 31, 2012 Joint Ventures	May 31, 2012 Exchange of Productive Assets	Jul. 31, 2011 Exchange of Productive Assets	May 31, 2011 Exchange of Productive Assets	May 31, 2012 Minimum	May 31, 2012 Maximum	May 31, 2012 Cement Facility	May 31, 2012 Life Insurance Policies	May 31, 2011 Life Insurance Policies	May 31, 2010 Life Insurance Policies	Apr. 30, 2012 Production Line
Summary Of Significant Accounting Policies [Line Items]
Equity interest in joint venture	40.00%
Fair value of long-term debt, including current portion	$ 646,800,000	$ 691,500,000
Long-term debt, carrying amount	658,163,000	652,476,000
Maturity period for investments to be classified cash and cash equivalents, days	90 days
Long-lived assets useful life																								10 years	25 years	40 years
Goodwill resulting from acquisition	1,715,000	1,715,000
Percentage of tax benefit likely to be realized upon ultimate settlement	50.00%
Real estate acquired for development	7,600,000	6,000,000
Life insurance contracts recorded net cash	700,000	700,000
Insurance policy distributions	94,400,000	87,700,000
Proceeds from life insurance policies																											7,300,000	7,800,000	10,600,000
Joint venture agreement date	2011-11
Number of plants contributed														7
Joint venture debt guaranteed percentage	50.00%					100.00%									50.00%
Joint venture debt guaranteed	13,000,000
Joint venture maturity date																				Nov. 18, 2013
Fair value of equity	13,000,000
Revenue recognition gain	8,900,000
Partner's percentage in the venture						60.00%
Equity losses in joint venture	(500,000)
Total plants operated by the joint venture																19		2
Deferred other charges	20,400,000	19,500,000
Debt issuance costs	13,000,000	13,200,000
Other credits	96,400,000	87,300,000
Gains from sale or exchange of operating assets and emission credit	70,100,000	15,400,000	4,800,000
Gain on asset exchange							5,400,000	1,700,000	1,400,000	2,500,000	1,700,000	3,400,000	20,800,000								10,500,000	1,600,000	12,000,000							30,900,000
Increase in aggregate property, plant and equipment																						6,100,000	17,400,000
Number of Assets Acquired In Noncash Asset Exchange																	3
Number of Assets Acquired In Noncash Asset Exchange																	7		4
Equity interest	40.00%
Fair value of equity interest	13,000,000
Gain in fair value of equity interest	8,900,000
Number of production facilities				5
Oil and gas lease bonuses and royalties	1,300,000	3,100,000	1,100,000
Restructuring charges	3,216,000				2,600,000
Financial Based Compensation	$ 5,000,000