Pensions and Other Postretirement Benefits - Additional Information (Detail) (USD $)	12 Months Ended
	Aug. 31, 2012 D Contract	Aug. 31, 2011	Aug. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Number of defined benefit plans	2
Employees covered under noncontributory defined benefit pension plans (in percentage)	0.57%
Expected long-term return on assets assumption used to calculate net periodic pension expense (in percentage)	0.07%
Redemption requests notice period (in days)	110
Employer contributions	$ 4,100,000	$ 6,400,000	$ 3,400,000
Minimum pension plan funding contribution during fiscal 2012	1,100,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return on assets assumption used to calculate net periodic pension expense (in percentage)	8.00%	8.00%	8.00%
Hypothetical decrease in the expected return on assets assumption, to determine impact on expense (in percentage)	50.00%
Estimated increase in expense resulting from a hypothetical decrease of 50 bps in the expected return on plan assets assumption	200,000
Discount rate (in percentage)	5.87%	5.64%	5.98%
Hypothetical decrease in the discount rate assumption, to determine impact on expense (in percentage)	4.28%
Estimated increase in expense resulting from a hypothetical decrease of 25 bps in the discount rate assumption	260,000
Defined Benefit Plan, Amortization of Net Gains (Losses), next fiscal year	1,930,000
Employer contributions	4,052,000	6,416,000
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate (in percentage)	5.87%	5.64%	5.98%
Hypothetical decrease in the discount rate assumption, to determine impact on expense (in percentage)	0.25%
Estimated increase in expense resulting from a hypothetical decrease of 25 bps in the discount rate assumption	100,000
Defined Benefit Plan, Amortization of Net Gains (Losses), next fiscal year	270,000
Employer contributions	$ 522,000	$ 497,000