Derivative and Hedging Financial Instruments - Summary of Volumes and Average Contract Prices of Contracts (Detail)	Jun. 30, 2015 MMBTU $ / MMBTU	Aug. 20, 2014 $ / MMBTU	May. 21, 2014 $ / MMBTU
Morgan Stanley Fixed III [Member]
Derivative [Line Items]
Volumes (MMBtu)	5,903,877
Morgan Stanley Fixed III [Member] | 2015 [Member]
Derivative [Line Items]
Volumes (MMBtu)	1,333,640
Commodity contracts, Basis Swap Fixed Price/mmbtu | $ / MMBTU	(1.12)
Morgan Stanley Fixed III [Member] | 2016 [Member]
Derivative [Line Items]
Volumes (MMBtu)	1,842,098
Commodity contracts, Basis Swap Fixed Price/mmbtu | $ / MMBTU	(1.12)
Morgan Stanley Fixed III [Member] | 2017 [Member]
Derivative [Line Items]
Volumes (MMBtu)	1,518,648
Commodity contracts, Basis Swap Fixed Price/mmbtu | $ / MMBTU	(1.12)
Morgan Stanley Fixed III [Member] | 2018 [Member]
Derivative [Line Items]
Volumes (MMBtu)	1,209,491
Commodity contracts, Basis Swap Fixed Price/mmbtu | $ / MMBTU	(1.12)
Morgan Stanley Fixed I [Member]
Derivative [Line Items]
Volumes (MMBtu)	9,350,876
Commodity contracts, Basis Swap Fixed Price/mmbtu | $ / MMBTU			(4.11)
Morgan Stanley Fixed I [Member] | 2015 [Member]
Derivative [Line Items]
Volumes (MMBtu)	1,857,538
Commodity contracts, Weighted- Average Fixed Price/mmbtu | $ / MMBTU	4.11
Morgan Stanley Fixed I [Member] | 2016 [Member]
Derivative [Line Items]
Volumes (MMBtu)	3,002,489
Commodity contracts, Weighted- Average Fixed Price/mmbtu | $ / MMBTU	3.27
Morgan Stanley Fixed I [Member] | 2017 [Member]
Derivative [Line Items]
Volumes (MMBtu)	2,495,153
Commodity contracts, Weighted- Average Fixed Price/mmbtu | $ / MMBTU	3.27
Morgan Stanley Fixed I [Member] | 2018 [Member]
Derivative [Line Items]
Volumes (MMBtu)	1,995,696
Commodity contracts, Weighted- Average Fixed Price/mmbtu | $ / MMBTU	3.27
Morgan Stanley Fixed II [Member]
Derivative [Line Items]
Volumes (MMBtu)	3,211,664
Commodity contracts, Basis Swap Fixed Price/mmbtu | $ / MMBTU		(3.92)
Morgan Stanley Fixed II [Member] | 2015 [Member]
Derivative [Line Items]
Volumes (MMBtu)	844,368
Commodity contracts, Weighted- Average Fixed Price/mmbtu | $ / MMBTU	3.92
Morgan Stanley Fixed II [Member] | 2016 [Member]
Derivative [Line Items]
Volumes (MMBtu)	992,431
Commodity contracts, Weighted- Average Fixed Price/mmbtu | $ / MMBTU	3.27
Morgan Stanley Fixed II [Member] | 2017 [Member]
Derivative [Line Items]
Volumes (MMBtu)	771,407
Commodity contracts, Weighted- Average Fixed Price/mmbtu | $ / MMBTU	3.27
Morgan Stanley Fixed II [Member] | 2018 [Member]
Derivative [Line Items]
Volumes (MMBtu)	603,458
Commodity contracts, Weighted- Average Fixed Price/mmbtu | $ / MMBTU	3.27