Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2012	May 31, 2011
Pension and Other Postretirement Benefits Disclosure [Line Items]
Service cost	$ 370	$ 376	$ 1,060	$ 1,136
Interest cost	1,986	1,441	5,609	4,259
Expected long-term return on plan assets	(1,650)	(1,118)	(4,524)	(3,315)
Amortization of prior service cost	(7)	(6)	(21)	(19)
Recognized actuarial loss	308	447	913	1,453
Curtailment gain				(1,874)
Net periodic benefit cost (gain)	$ 1,007	$ 1,140	$ 3,037	$ 1,640