Segment Information - Industry Segment Results (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Loss on Commodity Derivative Instruments	$ 115,142	$ (195,376)
Other Operating Income	4,958	3,197
Total Revenue	416,359	278,431
Total Operating Expense	843,300	308,827
Earnings (Loss) Before Income Tax	(457,804)	(76,210)
Segment Assets	8,528,950	8,777,361	$ 9,060,806
Depreciation, Depletion and Amortization	129,164	125,161
Capital Expenditures	152,049	299,138
Equity in earnings of unconsolidated affiliates	(161)	503
Impairment of Goodwill	473,045	0
Direct Energy Business Marketing LLC
Segment Reporting Information [Line Items]
Total Revenue	45,656	67,769
NJR Energy Services Company
Segment Reporting Information [Line Items]
Total Revenue	32,176	66,001
Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	296,259	470,610
Earnings (Loss) Before Income Tax	(476,097)	(73,846)
Equity in earnings of unconsolidated affiliates	161	503
Investments in unconsolidated equity affiliates	16,549	17,860
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Loss on Commodity Derivative Instruments	0	0
Other Operating Income	0	0
Total Revenue	0	0
Total Operating Expense	0	0
Earnings (Loss) Before Income Tax	18,293	(2,364)
Segment Assets	147,094	137,564
Depreciation, Depletion and Amortization	0	0
Capital Expenditures	0	0
Intersegment Eliminations
Segment Reporting Information [Line Items]
Loss on Commodity Derivative Instruments	0	0
Other Operating Income	(508)	(61)
Total Revenue	(62,443)	(54,187)
Total Operating Expense	(62,443)	(54,187)
Earnings (Loss) Before Income Tax	0	0
Segment Assets	(158,615)	(10,026)
Depreciation, Depletion and Amortization	0	0
Capital Expenditures	0	0
E&P \| Operating Segments
Segment Reporting Information [Line Items]
Loss on Commodity Derivative Instruments	115,142	(195,376)
Other Operating Income	5,466	3,258
Total Revenue	398,461	260,049
Total Operating Expense	404,828	338,052
Earnings (Loss) Before Income Tax	(46,553)	(106,430)
Segment Assets	6,785,652	6,638,207
Depreciation, Depletion and Amortization	119,152	117,075
Capital Expenditures	119,393	223,791
E&P \| Operating Segments \| Reportable Subsegments \| Marcellus Shale
Segment Reporting Information [Line Items]
Loss on Commodity Derivative Instruments	68,452	(27,458)
Other Operating Income	0	0
Total Revenue	247,496	265,799
Total Operating Expense	183,172	178,868
Earnings (Loss) Before Income Tax	64,324	86,931
Intercompany gathering fee	59,176	53,462
E&P \| Operating Segments \| Reportable Subsegments \| Utica Shale
Segment Reporting Information [Line Items]
Loss on Commodity Derivative Instruments	18,000	(9,601)
Other Operating Income	0	0
Total Revenue	59,450	83,350
Total Operating Expense	48,817	50,333
Earnings (Loss) Before Income Tax	10,633	33,017
Intercompany gathering fee	2,759	664
E&P \| Operating Segments \| Reportable Subsegments \| Coalbed Methane
Segment Reporting Information [Line Items]
Loss on Commodity Derivative Instruments	9,687	(4,302)
Other Operating Income	0	0
Total Revenue	40,410	45,533
Total Operating Expense	34,254	32,634
Earnings (Loss) Before Income Tax	6,156	12,899
E&P \| Operating Segments \| Reportable Subsegments \| Other Gas
Segment Reporting Information [Line Items]
Loss on Commodity Derivative Instruments	19,003	(154,015)
Other Operating Income	5,466	3,258
Total Revenue	51,105	(134,633)
Total Operating Expense	138,585	76,217
Earnings (Loss) Before Income Tax	(127,666)	(239,277)
CNXM \| Operating Segments
Segment Reporting Information [Line Items]
Loss on Commodity Derivative Instruments	0	0
Other Operating Income	0	0
Total Revenue	80,341	72,569
Total Operating Expense	500,915	24,962
Earnings (Loss) Before Income Tax	(429,544)	32,584
Segment Assets	1,754,819	2,011,616
Depreciation, Depletion and Amortization	10,012	8,086
Capital Expenditures	32,656	75,347
Oil and Gas
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	251,494	435,946
Oil and Gas \| Corporate, Non-Segment
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Oil and Gas \| Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Oil and Gas \| E&P \| Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	251,494	435,946
Oil and Gas \| E&P \| Operating Segments \| Reportable Subsegments \| Marcellus Shale
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	179,044	293,257
Oil and Gas \| E&P \| Operating Segments \| Reportable Subsegments \| Utica Shale
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	41,450	92,951
Oil and Gas \| E&P \| Operating Segments \| Reportable Subsegments \| Coalbed Methane
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	30,723	49,835
Oil and Gas \| E&P \| Operating Segments \| Reportable Subsegments \| Other Gas
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	277	(97)
Oil and Gas \| CNXM \| Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Purchased Gas Revenue
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	26,359	16,221
Purchased Gas Revenue \| Corporate, Non-Segment
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Purchased Gas Revenue \| Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Purchased Gas Revenue \| E&P \| Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	26,359	16,221
Purchased Gas Revenue \| E&P \| Operating Segments \| Reportable Subsegments \| Marcellus Shale
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	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
Purchased Gas Revenue \| E&P \| Operating Segments \| Reportable Subsegments \| Coalbed Methane
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Purchased Gas Revenue \| E&P \| Operating Segments \| Reportable Subsegments \| Other Gas
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	26,359	16,221
Purchased Gas Revenue \| CNXM \| Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Midstream Revenue
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	18,406	18,443
Midstream Revenue \| Corporate, Non-Segment
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Midstream Revenue \| Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	(61,935)	(54,126)
Midstream Revenue \| E&P \| Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Midstream Revenue \| E&P \| Operating Segments \| Reportable Subsegments \| Marcellus Shale
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Midstream Revenue \| E&P \| Operating Segments \| Reportable Subsegments \| Utica Shale
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Midstream Revenue \| E&P \| Operating Segments \| Reportable Subsegments \| Coalbed Methane
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Midstream Revenue \| E&P \| Operating Segments \| Reportable Subsegments \| Other Gas
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	0	0
Midstream Revenue \| CNXM \| Operating Segments
Segment Reporting Information [Line Items]
Revenue from Contracts with Customers	$ 80,341	$ 72,569

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