Derivative and Hedging Financial Instruments - Summary of Volumes and Average Contract Prices of Contracts (Detail)	Dec. 31, 2015 MMBTU $ / MMBTU	Dec. 23, 2014 $ / MMBTU	Aug. 20, 2014 $ / MMBTU
Morgan Stanley Restrike [Member]
Derivative [Line Items]
Volumes (MMBtu) | MMBTU	10,263,943
Commodity contracts, Basis Swap Fixed Price/mmbtu | $ / MMBTU			(3.92)
Morgan Stanley Restrike [Member] | 2016 [Member]
Derivative [Line Items]
Volumes (MMBtu) | MMBTU	4,166,789
Commodity contracts, Weighted- Average Fixed Price/mmbtu | $ / MMBTU	3.27
Morgan Stanley Restrike [Member] | 2017 [Member]
Derivative [Line Items]
Volumes (MMBtu) | MMBTU	3,300,403
Commodity contracts, Weighted- Average Fixed Price/mmbtu | $ / MMBTU	3.27
Morgan Stanley Restrike [Member] | 2018 [Member]
Derivative [Line Items]
Volumes (MMBtu) | MMBTU	2,796,751
Commodity contracts, Weighted- Average Fixed Price/mmbtu | $ / MMBTU	3.27
Morgan Stanley Fixed III [Member]
Derivative [Line Items]
Volumes (MMBtu) | MMBTU	4,747,755
Commodity contracts, Basis Swap Fixed Price/mmbtu | $ / MMBTU		(1.12)
Morgan Stanley Fixed III [Member] | 2016 [Member]
Derivative [Line Items]
Volumes (MMBtu) | MMBTU	1,878,290
Commodity contracts, Basis Swap Fixed Price/mmbtu | $ / MMBTU	(1.12)
Morgan Stanley Fixed III [Member] | 2017 [Member]
Derivative [Line Items]
Volumes (MMBtu) | MMBTU	1,539,998
Commodity contracts, Basis Swap Fixed Price/mmbtu | $ / MMBTU	(1.12)
Morgan Stanley Fixed III [Member] | 2018 [Member]
Derivative [Line Items]
Volumes (MMBtu) | MMBTU	1,329,467
Commodity contracts, Basis Swap Fixed Price/mmbtu | $ / MMBTU	(1.12)