Major classes of assets and liabilities held for sale (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Total current assets held for sale	$ 14,391	$ 54,847
Noncurrent assets:
Total noncurrent assets held for sale	196,664	$ 561,617
Pronghorn assets held for sale [Member] | Disposal group, held-for-sale, not discontinued operations [Member]
Current assets:
Prepayments and other current assets	68
Total current assets held for sale	68
Noncurrent assets:
Net property, plant and equipment	93,424
Goodwill	9,737
Less allowance for impairment of assets held for sale	2,311
Total noncurrent assets held for sale	100,850
Total assets held for sale	100,918
Fair value impairment	2,300
Fair value impairment, net of tax	$ 1,400