Derivative Activities - Effects of Derivatives on Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivative Fair Value Income (Loss)	$ 25,024	$ (88,426)	$ 111,195	$ 165,557	$ (250,057)	$ 64,556	$ (162,798)	$ 86,908	$ 213,350	$ (261,391)	$ 416,364
Swaptions
Derivative [Line Items]
Derivative Fair Value Income (Loss)									6,534	0	0
Re-purchased Swaps
Derivative [Line Items]
Derivative Fair Value Income (Loss)									0	0	851
Collars
Derivative [Line Items]
Derivative Fair Value Income (Loss)									18,132	(6,926)	16,539
Basis Swaps
Derivative [Line Items]
Derivative Fair Value Income (Loss)									(4,647)	29,154	954
Puts
Derivative [Line Items]
Derivative Fair Value Income (Loss)									10,929	(18,201)	0
Calls
Derivative [Line Items]
Derivative Fair Value Income (Loss)									987	(18)	0
Commodity | Swaps
Derivative [Line Items]
Derivative Fair Value Income (Loss)									181,095	(265,466)	398,020
Freight | Commodity | Swaps
Derivative [Line Items]
Derivative Fair Value Income (Loss)									$ 320	$ 66	$ 0