Discontinued Operations (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2015 USD ($) item	Dec. 31, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2013 USD ($)
Discontinued operations
Loss from discontinued operations, net of income taxes	$ (216)	$ (67)
Coal Cleaning Business | Discontinued Operations, Disposed of by Sale
Discontinued operations
Remaining assets held for sale				$ 0
Revenue	0	0
Loss from operations of discontinued operations before income taxes	(338)	(22)
Loss on disposal	(8)	(45)
Income tax benefit	130	0
Loss from discontinued operations, net of income taxes	$ (216)	$ (67)
Number of sales transactions in which the buyer agreed to assume the lease and certain reclamation obligations | item	1
Number of reclamation obligations | item	1
Accrued liability for reclamation obligations	$ 7,200		$ 7,400