Commitments And Contingencies (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Nov. 30, 2011	Feb. 29, 2012	Feb. 28, 2011	Aug. 31, 2011
Commitments And Contingencies [Line Items]
Environmental remediation expense	$ 7,200	$ 7,225	$ 713
Total environmental remediation liabilities		7,937	1,206	1,540
Other current liabilities		2,737	1,206	1,540
Other noncurrent liabilities		$ 5,200
Maximum [Member]
Commitments And Contingencies [Line Items]
Period of environmental remediation and operating cost (in years)	10
Minimum [Member]
Commitments And Contingencies [Line Items]
Period of environmental remediation and operating cost (in years)	5