Property, Plant and Equipment (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 28, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment		$ 9,276,800		$ 9,276,800		$ 9,316,495
Less: Accumulated Depreciation, Depletion and Amortization		2,508,188		2,508,188		3,526,742
Total Property, Plant and Equipment—Net		6,768,612		6,768,612		5,789,753
Impairment on Knox		0	$ 0	0	$ 137,865
Gas Segment [Member]
Property, Plant and Equipment [Line Items]
Intangible drilling cost		3,980,330		3,980,330		3,849,689
Proved gas properties		939,815		939,815		1,999,891
Gas gathering equipment		2,080,909		2,080,909		1,182,234
Unproved gas properties		1,105,813		1,105,813		919,733
Gas wells and related equipment		789,333		789,333		834,120
Surface land and other equipment		308,397		308,397		309,602
Other gas assets		72,203		72,203		221,226
Total Property, Plant and Equipment		9,276,800		9,276,800		9,316,495
Less: Accumulated Depreciation, Depletion and Amortization		2,508,188		2,508,188		3,526,742
Total Property, Plant and Equipment—Net		$ 6,768,612		$ 6,768,612		$ 5,789,753
Knox and Coalfield [Member]
Property, Plant and Equipment [Line Items]
Impairment on Knox	$ 137,865