Summary Of Significant Accounting Policies - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended	9 Months Ended		3 Months Ended		9 Months Ended			1 Months Ended			9 Months Ended				3 Months Ended
	Feb. 28, 2013	May 31, 2012	Feb. 28, 2013 Co-venturer	Feb. 28, 2013 Additional	Feb. 28, 2013 Real Estate	Feb. 29, 2012 Real Estate	Feb. 28, 2013 Real Estate	Feb. 29, 2012 Real Estate	Feb. 29, 2012 Cement	Jul. 31, 2011 Ready-Mix Concrete Property	Jul. 31, 2011 Nonoperating Development Properties Property	Jul. 31, 2011 Exchange of Productive Assets	Feb. 28, 2013 Riverside Defined Benefit Plans Employee	Feb. 28, 2013 Minimum	Feb. 28, 2013 Maximum	Feb. 28, 2013 Cement Facility	Feb. 28, 2013 Restricted Stock Units (RSUs)
Summary Of Significant Accounting Policies [Line Items]
Equity interest in joint venture	40.00%	40.00%
Fair value of long-term debt, including current portion	$ 718,700,000	$ 646,800,000
Long-term debt, carrying amount	660,208,000	658,163,000
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	7,300,000	7,600,000
Life insurance contracts recorded net cash	1,600,000	700,000
Insurance policy distributions	99,400,000	94,400,000
Joint venture agreement date	2011 11
Joint venture debt guaranteed percentage	50.00%		100.00%	50.00%
Fair value of equity	14,100,000	12,500,000
Partner's percentage in the venture			60.00%
Equity income in joint venture	1,600,000
Deferred other charges	19,500,000	20,400,000
Debt issuance costs	11,600,000	13,000,000
Other credits	88,100,000	96,400,000
Approximate number of employees and retirees of subsidiary													600
Accumulated other comprehensive loss, adjustments related to defined benefit retirement plan and postretirement health benefit plan, net of tax	23,900,000	24,500,000
Accumulated other comprehensive loss, adjustments related to defined benefit retirement plan and postretirement health benefit plan, tax	5,700,000	6,000,000
Gain on asset exchange					1,900,000	1,000,000	4,800,000	1,700,000	2,500,000			2,100,000
Number of assets acquired in noncash asset exchange										3
Number of assets disposed of in noncash asset exchange										7	4
Increase in aggregate property, plant and equipment												$ 6,100,000
Award vesting period																	4 years