Pension and Post-Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Nov. 30, 2012	Nov. 30, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 486	$ 380
Interest cost	662	682
Expected return on plan assets	(717)	(729)
Amortization of prior service cost	60	57
Amortization of actuarial losses	483	193
Net periodic benefit cost	974	583
Postretirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	59	57
Interest cost	215	243
Amortization of prior service cost	(38)	(38)
Amortization of actuarial losses	67
Net periodic benefit cost	$ 303	$ 262