Derivative Activities - Effects of Non-Hedge Derivatives on Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
Derivative [Line Items]
Derivative Fair Value Income (Loss)	$ 86,908	$ 122,839
Collars
Derivative [Line Items]
Derivative Fair Value Income (Loss)	0	8,415
Basis Swaps
Derivative [Line Items]
Derivative Fair Value Income (Loss)	7,275	(11,353)
Commodity \| Swaps
Derivative [Line Items]
Derivative Fair Value Income (Loss)	79,644	125,777
Freight \| Swaps
Derivative [Line Items]
Derivative Fair Value Income (Loss)	$ (11)	$ 0

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration