Pension and Post-Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2013	May 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 486	$ 380	$ 1,458	$ 1,140
Interest cost	662	682	1,986	2,046
Expected return on plan assets	(717)	(729)	(2,151)	(2,187)
Amortization of prior service cost	60	57	180	171
Amortization of actuarial losses	483	193	1,449	579
Net periodic benefit cost	974	583	2,922	1,749
Postretirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	59	57	177	171
Interest cost	215	243	645	729
Amortization of prior service cost	(38)	(38)	(114)	(114)
Amortization of actuarial losses	67		201
Net periodic benefit cost	$ 303	$ 262	$ 909	$ 786