Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Aug. 31, 2013	Aug. 31, 2012	Aug. 31, 2011
Statement Of Income And Comprehensive Income [Abstract]
Change in fair value of derivatives, tax	$ (457)	$ (1,419)	$ 3,690
Loss (gain) from derivative transactions reclassified into earnings from other comprehensive income, tax	(1,987)	(863)	4,494
Actuarial gain (loss) on post-retirement liabilities, tax	(5,547)	5,722	(2,450)
Loss from postretirement liabilities, tax	$ 869	$ 242	$ 601