Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 127,811		$ 127,811		$ 190,648
Less accumulated depreciation, depletion and amortization	(95,853)		(95,853)		(144,323)
Property and equipment, net	31,958		31,958		46,325
Depreciation, depletion and amortization, excluding amount under capital leases	3,210	$ 4,514	10,742	$ 14,385
Amortization of property and equipment under capital leases	30	0	30	0
Total depreciation, depletion and amortization	3,240	$ 4,514	10,772	$ 14,385
Marketing
Property, Plant and Equipment [Line Items]
Property and equipment, gross	56,913		56,913		56,907
Transportation
Property, Plant and Equipment [Line Items]
Property and equipment, gross	70,790		70,790		70,849
Oil and natural gas (successful efforts)
Property, Plant and Equipment [Line Items]
Property and equipment, gross	0		0		62,784
Other
Property, Plant and Equipment [Line Items]
Property and equipment, gross	108		108		$ 108
Property and equipment recorded under capital leases
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,800		1,800
Less accumulated depreciation, depletion and amortization	$ (100)		$ (100)