Segment Information - Industry Segment Results (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Other Operating Income	$ 3,753		$ 2,923	$ 8,711	$ 6,120
Total Revenue	148,841		605,032	565,200	883,463
Total Operating Expense	262,512		331,804	1,105,811	640,633
Earnings Before Income Tax	(159,132)		233,485	(616,937)	157,275
Segment Assets	8,319,684		9,146,697	8,319,684	9,146,697	$ 9,060,806
Depreciation, Depletion and Amortization	113,545		128,999	242,709	254,159
Capital Expenditures	134,852		329,227	286,901	628,365
Gain on Commodity Derivative Instruments	(63,303)		221,581	51,839	26,205
Equity in earnings of unconsolidated affiliates				(1,421)	1,030
Impairment of Goodwill	0	$ 473,045	0	473,045	0
Natural Gas | Commodity Swap
Segment Reporting Information [Line Items]
Gain on Commodity Derivative Instruments	(28,970)		245,412	129,155	167,701
Direct Energy Business Marketing LLC
Segment Reporting Information [Line Items]
Total Revenue	33,711		48,476	79,367	116,245
NJR Energy Services Company
Segment Reporting Information [Line Items]
Total Revenue					94,447
Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	208,391		380,528	504,650	851,138
Earnings Before Income Tax	(161,967)		232,674	(638,064)	158,828
Equity in earnings of unconsolidated affiliates	(1,259)		527	(1,421)	1,030
Investments in unconsolidated equity affiliates	15,159		17,637	15,159	17,637
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Other Operating Income	0		0	0	0
Total Revenue	0		0	0	0
Total Operating Expense	0		0	0	0
Earnings Before Income Tax	2,835		811	21,127	(1,553)
Segment Assets	134,047		146,203	134,047	146,203
Depreciation, Depletion and Amortization	0		0	0	0
Capital Expenditures	0		0	0	0
Gain on Commodity Derivative Instruments	0		0	0	0
Intersegment Eliminations
Segment Reporting Information [Line Items]
Other Operating Income	(495)		(115)	(1,003)	(176)
Total Revenue	(54,453)		(59,670)	(116,896)	(113,857)
Total Operating Expense	(54,453)		(59,670)	(116,896)	(113,857)
Earnings Before Income Tax	0		0	0	0
Segment Assets	(153,991)		(3,041)	(153,991)	(3,041)
Depreciation, Depletion and Amortization	0		0	0	0
Capital Expenditures	0		0	0	0
Gain on Commodity Derivative Instruments	0		0	0	0
E&P | Operating Segments
Segment Reporting Information [Line Items]
Other Operating Income	4,248		3,038	9,714	6,296
Total Revenue	137,145		586,252	535,606	846,301
Total Operating Expense	291,770		365,519	696,598	703,571
Earnings Before Income Tax	(192,263)		188,260	(238,816)	81,830
Segment Assets	6,584,989		6,887,043	6,584,989	6,887,043
Depreciation, Depletion and Amortization	102,901		120,705	222,053	237,780
Capital Expenditures	120,474		224,684	239,867	448,475
Gain on Commodity Derivative Instruments	(63,303)		221,581	51,839	26,205
E&P | Operating Segments | Reportable Subsegments | Marcellus Shale
Segment Reporting Information [Line Items]
Other Operating Income	0		0	0	0
Total Revenue	202,486		244,088	449,982	509,887
Total Operating Expense	144,857		193,707	328,029	372,575
Earnings Before Income Tax	57,629		50,381	121,953	137,312
Gain on Commodity Derivative Instruments	79,006		6,831	147,458	(20,627)
Intercompany gathering fee	51,903		2,055	111,079	112,476
E&P | Operating Segments | Reportable Subsegments | Utica Shale
Segment Reporting Information [Line Items]
Other Operating Income	0		0	0	0
Total Revenue	50,404		67,960	109,854	151,310
Total Operating Expense	42,876		50,019	91,693	101,365
Earnings Before Income Tax	7,528		17,941	18,161	49,945
Gain on Commodity Derivative Instruments	21,257		2,747	39,257	(6,854)
Intercompany gathering fee	59,014		541	4,814	1,205
E&P | Operating Segments | Reportable Subsegments | Coalbed Methane
Segment Reporting Information [Line Items]
Other Operating Income	0		0	0	0
Total Revenue	35,934		40,723	76,344	86,256
Total Operating Expense	29,420		33,120	63,674	65,754
Earnings Before Income Tax	6,514		7,603	12,670	20,502
Gain on Commodity Derivative Instruments	13,005		1,085	22,692	(3,217)
E&P | Operating Segments | Reportable Subsegments | Other Gas
Segment Reporting Information [Line Items]
Other Operating Income	4,248		3,038	9,714	6,296
Total Revenue	(151,679)		233,481	(100,574)	98,848
Total Operating Expense	74,617		88,673	213,202	163,877
Earnings Before Income Tax	(263,934)		112,335	(391,600)	(125,929)
Gain on Commodity Derivative Instruments	(176,571)		210,918	(157,568)	56,903
E&P | Operating Segments | Reportable Subsegments | Other Gas | Natural Gas | Commodity Swap
Segment Reporting Information [Line Items]
Gain on Commodity Derivative Instruments	29,015			83,997
Midstream | Operating Segments
Segment Reporting Information [Line Items]
Other Operating Income	0		0	0	0
Total Revenue	66,149		78,450	146,490	151,019
Total Operating Expense	25,195		25,955	526,109	50,919
Earnings Before Income Tax	30,296		44,414	(399,248)	76,998
Segment Assets	1,754,639		2,116,492	1,754,639	2,116,492
Depreciation, Depletion and Amortization	10,644		8,294	20,656	16,379
Capital Expenditures	14,378		104,543	47,034	179,890
Gain on Commodity Derivative Instruments	0		0	0	0
Oil and Gas
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	175,776		342,865	427,270	778,811
Oil and Gas | Corporate, Non-Segment
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Oil and Gas | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Oil and Gas | E&P | Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	175,776		342,865	427,270	778,811
Oil and Gas | E&P | Operating Segments | Reportable Subsegments | Marcellus Shale
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	123,480		237,257	302,524	530,514
Oil and Gas | E&P | Operating Segments | Reportable Subsegments | Utica Shale
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	29,147		65,213	70,597	158,164
Oil and Gas | E&P | Operating Segments | Reportable Subsegments | Coalbed Methane
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	22,929		39,638	53,652	89,473
Oil and Gas | E&P | Operating Segments | Reportable Subsegments | Other Gas
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	220		757	497	660
Oil and Gas | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Purchased Gas Revenue
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	20,424		18,768	46,783	34,989
Purchased Gas Revenue | Corporate, Non-Segment
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Purchased Gas Revenue | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Purchased Gas Revenue | E&P | Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	20,424		18,768	46,783	34,989
Purchased Gas Revenue | E&P | Operating Segments | Reportable Subsegments | Marcellus Shale
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Purchased Gas Revenue | E&P | Operating Segments | Reportable Subsegments | Utica Shale
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Purchased Gas Revenue | E&P | Operating Segments | Reportable Subsegments | Coalbed Methane
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Purchased Gas Revenue | E&P | Operating Segments | Reportable Subsegments | Other Gas
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	20,424		18,768	46,783	34,989
Purchased Gas Revenue | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Midstream Revenue
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	12,191		18,895	30,597	37,338
Midstream Revenue | Corporate, Non-Segment
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Midstream Revenue | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	(53,958)		(59,555)	(115,893)	(113,681)
Midstream Revenue | E&P | Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Midstream Revenue | E&P | Operating Segments | Reportable Subsegments | Marcellus Shale
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Midstream Revenue | E&P | Operating Segments | Reportable Subsegments | Utica Shale
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Midstream Revenue | E&P | Operating Segments | Reportable Subsegments | Coalbed Methane
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Midstream Revenue | E&P | Operating Segments | Reportable Subsegments | Other Gas
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0		0	0	0
Midstream Revenue | Midstream | Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	$ 66,149		$ 78,450	$ 146,490	$ 151,019