Derivative Activities - Effects of Derivatives on Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Derivative Fair Value (Loss) Income	$ (103,290)	$ 111,195	$ (117,299)	$ 276,752
Swaptions
Derivative [Line Items]
Derivative Fair Value (Loss) Income	(6,592)		(2,993)
Collars
Derivative [Line Items]
Derivative Fair Value (Loss) Income	11	4,790	(66)	14,265
Puts
Derivative [Line Items]
Derivative Fair Value (Loss) Income		3,012		9,719
Calls
Derivative [Line Items]
Derivative Fair Value (Loss) Income	152	529	329	1,040
Basis Swaps
Derivative [Line Items]
Derivative Fair Value (Loss) Income	(5,828)	9,304	(6,693)	(8,668)
Commodity | Swaps
Derivative [Line Items]
Derivative Fair Value (Loss) Income	(91,195)	93,567	(107,730)	260,319
Freight | Commodity | Swaps
Derivative [Line Items]
Derivative Fair Value (Loss) Income	$ 162	$ (7)	$ (146)	$ 77