Other Employee Benefits - Additional Information (Detail) (USD $)	12 Months Ended
	Aug. 31, 2013	Aug. 31, 2012	Aug. 31, 2011
Savings and Stock Ownership Plan [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Deferral maximum salary percentage	16.00%
Employer's match of the first 0% of an employee's salary contributed by that employee to the plan	100.00%
Percentage of salary under first plan	3.00%
Employer's match of the second 0% of an employee's salary contributed by that employee to the plan	50.00%
Company's matching contributions	$ 1,200,000	$ 1,000,000	$ 900,000
Postretirement Health Care and Life Insurance Benefits [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Pension and postretirement benefits expense, deferred compensation arrangement	5,900,000	5,100,000	4,500,000
Deferred Compensation Plan [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Pension and postretirement benefits expense, deferred compensation arrangement	177,000	179,000	197,000
Supplemental Executive Retirement Plans [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Pension and postretirement benefits expense, deferred compensation arrangement	271,000	258,000	370,000
Accrued pension plan obligation	$ 2,700,000