Components of Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,521	$ 1,617	$ 1,608
Interest cost	2,729	2,696	2,633
Expected return on plan assets	(2,914)	(2,234)	(2,022)
Amortization of prior service cost	228	228	244
Amortization of actuarial loss	773	1,441	1,312
Benefit cost	2,337	3,748	3,775
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	229	272	353
Interest cost	972	972	1,077
Amortization of prior service cost	(152)	(152)	(152)
Amortization of actuarial loss		65	294
Benefit cost	$ 1,049	$ 1,157	$ 1,572