Asset Retirement Obligations (Schedule of Asset Retirement Obligations) (Details) (USD $)
In Thousands, unless otherwise specified
6 Months Ended
Feb. 28, 2014
Asset Retirement Obligations [Abstract]  
Asset retirement obligations, August 31, 2013 $ 2,777
Liabilities incurred 428
Liabilities assumed 572
Liabilities settled   
Accretion 156
Asset retirement obligations, February 28, 2014 $ 3,933