Pensions and Other Postretirement Benefits - Summary of Pension and Other Postretirement Benefit Plans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Aug. 31, 2013	Aug. 31, 2012	Aug. 31, 2011
Change in plan assets:
Company contributions	$ 1,100	$ 4,100	$ 6,400
Balance, August 31, 2013	46,726
Pension Benefits [Member]
Change in benefit obligation:
Benefit obligation, beginning balance	62,989	47,545
Service cost	1,945	1,521	1,617
Interest cost	2,648	2,729	2,696
Amendments		212
Actuarial (gain) loss	(107)	619
Change in assumptions	(8,135)	12,359
Benefits paid	(2,062)	(1,996)
Benefit obligation, ending balance	57,278	62,989	47,545
Change in plan assets:
Balance, August 31, 2012	42,072	36,328
Actual return on plan assets	5,580	3,688
Company contributions	1,136	4,052
Benefits paid	(2,062)	(1,996)
Balance, August 31, 2013	46,726	42,072	36,328
Funded status:
Net liability - Plan assets less than projected benefit obligation	(10,552)	(20,917)
Recognized as:
Non-current accrued benefit liability	(10,552)	(20,917)
Net Amount Recognized	(10,552)	(20,917)
Other Benefits [Member]
Change in benefit obligation:
Benefit obligation, beginning balance	20,457	16,924
Service cost	235	229	272
Interest cost	860	972	972
Plan participants' contributions	106	119
Actuarial (gain) loss	267	(170)
Change in assumptions	(3,912)	3,024
Benefits paid	(657)	(641)
Benefit obligation, ending balance	17,356	20,457	16,924
Change in plan assets:
Company contributions	551	522
Plan participants' contributions	106	119
Benefits paid	(657)	(641)
Funded status:
Net liability - Plan assets less than projected benefit obligation	(17,356)	(20,457)
Recognized as:
Current accrued benefit liability	(760)	(750)
Non-current accrued benefit liability	(16,596)	(19,707)
Net Amount Recognized	$ (17,356)	$ (20,457)