Pensions and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Aug. 31, 2013	Aug. 31, 2012	Aug. 31, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,945	$ 1,521	$ 1,617
Interest cost	2,648	2,729	2,696
Expected return on plan assets	(2,869)	(2,914)	(2,234)
Amortization of prior service cost	241	228	228
Amortization of actuarial loss	1,932	773	1,441
Benefit cost	3,897	2,337	3,748
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	235	229	272
Interest cost	860	972	972
Amortization of prior service cost	(152)	(152)	(152)
Amortization of actuarial loss	267		65
Benefit cost	$ 1,210	$ 1,049	$ 1,157