Net Periodic Benefit Cost for Pension Plans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Feb. 28, 2013	Feb. 29, 2012	Feb. 28, 2013	Feb. 29, 2012
Pension and Other Postretirement Benefits Disclosure [Line Items]
Service cost	$ 510	$ 373	$ 1,026	$ 690
Interest cost	1,913	1,968	3,838	3,623
Expected long-term return on plan assets	(1,727)	(1,635)	(3,469)	(2,874)
Amortization of prior service cost	(7)	(7)	(13)	(14)
Recognized actuarial loss	686	301	1,367	605
Net periodic benefit cost	$ 1,375	$ 1,000	$ 2,749	$ 2,030