Pension and Post-Retirement Benefit Plans - Components of Net Periodic Benefit Cost (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 Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 486	$ 380	$ 972	$ 760
Interest cost	662	682	1,324	1,364
Expected return on plan assets	(717)	(729)	(1,434)	(1,458)
Amortization of prior service cost	60	57	120	114
Amortization of actuarial losses	483	193	966	386
Net periodic benefit cost	974	583	1,948	1,166
Postretirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	59	57	118	114
Interest cost	215	243	430	486
Amortization of prior service cost	(38)	(38)	(76)	(76)
Amortization of actuarial losses	67		134
Net periodic benefit cost	$ 303	$ 262	$ 606	$ 524