Derivative Activities - Schedule of Additional Information Related to Master Netting Arrangements with Derivative Counterparties (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Gross Amounts of Recognized Assets	$ 90,503	$ 77,079
Gross Amounts Offset in the Balance Sheet	(59,815)	(63,596)
Net Amounts of Assets Presented in the Balance Sheet	30,688	13,483
Gross Amounts of Recognized (Liabilities)	(108,640)	(253,096)
Gross Amounts Offset in the Balance Sheet	59,815	63,596
Net Amounts of (Liabilities) Presented in the Balance Sheet	(48,825)	(189,500)
Commodity | Swaps | Natural Gas
Derivative [Line Items]
Gross Amounts of Recognized Assets	37,288	13,213
Gross Amounts Offset in the Balance Sheet	(12,385)	(11,425)
Net Amounts of Assets Presented in the Balance Sheet	24,903	1,788
Gross Amounts of Recognized (Liabilities)	(10,805)	(158,359)
Gross Amounts Offset in the Balance Sheet	12,385	11,425
Net Amounts of (Liabilities) Presented in the Balance Sheet	1,580	(146,934)
Commodity | Swaps | Crude Oil
Derivative [Line Items]
Gross Amounts of Recognized Assets	7,133	9,356
Gross Amounts Offset in the Balance Sheet	(2,918)	(3,489)
Net Amounts of Assets Presented in the Balance Sheet	4,215	5,867
Gross Amounts of Recognized (Liabilities)	(1,031)	(13,206)
Gross Amounts Offset in the Balance Sheet	2,918	3,489
Net Amounts of (Liabilities) Presented in the Balance Sheet	1,887	(9,717)
Commodity | Swaps | NGLs (C2-Ethane)
Derivative [Line Items]
Gross Amounts of Recognized Assets	82	53
Gross Amounts Offset in the Balance Sheet	(82)	(53)
Net Amounts of Assets Presented in the Balance Sheet	0	0
Gross Amounts of Recognized (Liabilities)	(125)	(1,008)
Gross Amounts Offset in the Balance Sheet	82	53
Net Amounts of (Liabilities) Presented in the Balance Sheet	(43)	(955)
Commodity | Swaps | NGLs (C3-Propane)
Derivative [Line Items]
Gross Amounts of Recognized Assets	0
Gross Amounts Offset in the Balance Sheet	(2,956)
Net Amounts of Assets Presented in the Balance Sheet	(2,956)
Gross Amounts of Recognized (Liabilities)	(36,046)	(32,437)
Gross Amounts Offset in the Balance Sheet	2,956	0
Net Amounts of (Liabilities) Presented in the Balance Sheet	(33,090)	(32,437)
Commodity | Swaps | NGLs (NC4-Normal Butane)
Derivative [Line Items]
Gross Amounts of Recognized Assets	34	4
Gross Amounts Offset in the Balance Sheet	(4,340)	(4)
Net Amounts of Assets Presented in the Balance Sheet	(4,306)	0
Gross Amounts of Recognized (Liabilities)	(13,700)	(13,419)
Gross Amounts Offset in the Balance Sheet	4,340	4
Net Amounts of (Liabilities) Presented in the Balance Sheet	(9,360)	(13,415)
Commodity | Swaps | NGLs (C5-Natural Gasoline)
Derivative [Line Items]
Gross Amounts of Recognized Assets	115
Gross Amounts Offset in the Balance Sheet	(1,094)
Net Amounts of Assets Presented in the Balance Sheet	(979)
Gross Amounts of Recognized (Liabilities)	(4,678)	(12,176)
Gross Amounts Offset in the Balance Sheet	1,094	0
Net Amounts of (Liabilities) Presented in the Balance Sheet	(3,584)	(12,176)
Commodity | Swaps | Freight
Derivative [Line Items]
Gross Amounts of Recognized Assets	47	65
Gross Amounts Offset in the Balance Sheet	(47)	(65)
Net Amounts of Assets Presented in the Balance Sheet	0	0
Gross Amounts of Recognized (Liabilities)	(2)	0
Gross Amounts Offset in the Balance Sheet	47	65
Net Amounts of (Liabilities) Presented in the Balance Sheet	45	65
Commodity | Swaptions | Natural Gas
Derivative [Line Items]
Gross Amounts of Recognized Assets	9,092
Gross Amounts Offset in the Balance Sheet	(8,711)
Net Amounts of Assets Presented in the Balance Sheet	381
Gross Amounts of Recognized (Liabilities)	(16,694)
Gross Amounts Offset in the Balance Sheet	8,711
Net Amounts of (Liabilities) Presented in the Balance Sheet	(7,983)
Commodity | Basis Swaps | Natural Gas
Derivative [Line Items]
Gross Amounts of Recognized Assets	3,782	12,535
Gross Amounts Offset in the Balance Sheet	(2,774)	(9,437)
Net Amounts of Assets Presented in the Balance Sheet	1,008	3,098
Gross Amounts of Recognized (Liabilities)	(8,458)	(687)
Gross Amounts Offset in the Balance Sheet	2,774	9,437
Net Amounts of (Liabilities) Presented in the Balance Sheet	(5,684)	8,750
Commodity | Basis Swaps | NGLs (C3-Propane)
Derivative [Line Items]
Gross Amounts of Recognized Assets	18,169	17,396
Gross Amounts Offset in the Balance Sheet	(18,169)	(17,396)
Net Amounts of Assets Presented in the Balance Sheet	0	0
Gross Amounts of Recognized (Liabilities)	(17,072)	(18,138)
Gross Amounts Offset in the Balance Sheet	18,169	17,396
Net Amounts of (Liabilities) Presented in the Balance Sheet	1,097	(742)
Commodity | Collars | Natural Gas
Derivative [Line Items]
Gross Amounts of Recognized Assets	6,214	6,298
Gross Amounts Offset in the Balance Sheet	(2,101)	(6,298)
Net Amounts of Assets Presented in the Balance Sheet	4,113	0
Gross Amounts of Recognized (Liabilities)	0	(2,625)
Gross Amounts Offset in the Balance Sheet	2,101	6,298
Net Amounts of (Liabilities) Presented in the Balance Sheet	2,101	3,673
Commodity | Puts | Natural Gas
Derivative [Line Items]
Gross Amounts of Recognized Assets	8,547	18,159
Gross Amounts Offset in the Balance Sheet	(4,238)	(15,429)
Net Amounts of Assets Presented in the Balance Sheet	4,309	2,730
Gross Amounts of Recognized (Liabilities)	0	0
Gross Amounts Offset in the Balance Sheet	4,238	15,429
Net Amounts of (Liabilities) Presented in the Balance Sheet	4,238	15,429
Commodity | Calls | Natural Gas
Derivative [Line Items]
Gross Amounts of Recognized (Liabilities)	(29)	(1,041)
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of (Liabilities) Presented in the Balance Sheet	$ (29)	$ (1,041)