Derivative Activities - Effects of Derivatives on Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative Fair Value (Loss) Income	$ 100,698	$ (34,591)	$ (103,290)	$ (14,009)	$ 25,024	$ (88,426)	$ 111,195	$ 165,557	$ (51,192)	$ 213,350	$ (261,391)
Swaptions
Derivative [Line Items]
Derivative Fair Value (Loss) Income									(6,556)	6,534	0
Collars
Derivative [Line Items]
Derivative Fair Value (Loss) Income									17,583	18,132	(6,926)
Basis Swaps
Derivative [Line Items]
Derivative Fair Value (Loss) Income									(1,104)	(4,647)	29,154
Puts
Derivative [Line Items]
Derivative Fair Value (Loss) Income									0	10,929	(18,201)
Calls
Derivative [Line Items]
Derivative Fair Value (Loss) Income									(2,653)	987	(18)
Commodity | Swaps
Derivative [Line Items]
Derivative Fair Value (Loss) Income									(57,950)	181,095	(265,466)
Freight | Commodity | Swaps
Derivative [Line Items]
Derivative Fair Value (Loss) Income									$ (512)	$ 320	$ 66