Derivative Activities - Effects of Derivatives on Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Derivative Fair Value (Loss) Income	$ (34,591)	$ (88,426)	$ (151,890)	$ 188,326
Swaptions
Derivative [Line Items]
Derivative Fair Value (Loss) Income	7,093	(7,602)	4,100	(7,602)
Collars
Derivative [Line Items]
Derivative Fair Value (Loss) Income	(3,965)	956	(4,031)	15,221
Puts
Derivative [Line Items]
Derivative Fair Value (Loss) Income	0	(73)	0	9,646
Calls
Derivative [Line Items]
Derivative Fair Value (Loss) Income	197	104	526	1,144
Basis Swaps
Derivative [Line Items]
Derivative Fair Value (Loss) Income	(2,350)	6,113	(9,043)	(2,554)
Commodity | Swaps
Derivative [Line Items]
Derivative Fair Value (Loss) Income	(35,868)	(87,861)	(143,598)	172,457
Freight | Commodity | Swaps
Derivative [Line Items]
Derivative Fair Value (Loss) Income	$ 302	$ (63)	$ 156	$ 14