Consolidated Statements of Comprehensive Income (Loss) (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]
Net income (loss)	$ 4,007	$ (9,566)	$ (5,117)
Other comprehensive income (loss):
Change in fair value of derivatives, net of tax benefit (expense) of $(457), $(1,419) and $3,690	747	2,315	(6,018)
Loss (gain) from derivative transactions reclassified into earnings from other comprehensive income, net of tax benefit (expense) of $(1,987), $(863) and $4,494	(3,241)	(1,408)	7,331
Actuarial gain (loss) on postretirement liabilities, net of tax benefit (expense) of $(5,547), $5,722 and $(2,450)	9,049	(9,336)	3,997
Loss from postretirement liabilities reclassified to earnings, net of tax benefit of $869, $242 and $601	1,419	395	981
Other comprehensive income (loss)	7,974	(8,034)	6,291
Total comprehensive income (loss)	$ 11,981	$ (17,600)	$ 1,174