Segment Information Industry Segment Results (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Oil and Gas Sales Revenue									$ 793,248	$ 726,921	$ 1,004,924
Sales-Outside									1,858,830	2,015,957	2,621,798
Gain (Loss) on Hedging Activity									(141,021)	392,942	23,193
Sales Revenue, Services, Other									32,038	30,967	276,242
Sales-Purchased Gas									43,256	14,450	8,999
Freight-Outside	$ 12,519	$ 9,392	$ 10,295	$ 11,447	$ 13,110	$ 2,436	$ 2,750	$ 5,018	46,468	20,499	23,133
Segment Reporting - Intersegment Transfers									0	0	0
Total Revenue and Other Income									2,026,375	2,693,339	3,204,023
Sales Revenue, Services, Net									1,839,571	2,474,815	2,953,365
Income (Loss) from Continuing Operations before Income Taxes, Domestic									(525,955)	(475,705)	180,151
Total Assets	9,183,981		10,929,902						9,183,981	10,929,902	11,654,646
Depreciation, Depletion and Amortization									598,503	567,120	532,643
Segment Reporting - Capital Expenditures									226,820	982,934	1,459,452
Equity in Earnings of Affiliates									(53,078)	(54,897)	(49,791)
Total Reportable Business Segments
Segment Reporting Information [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Domestic									(248,132)	(273,863)	620,682
Total Assets	8,217,774		8,968,585						8,217,774	8,968,585
All Other [Member]
Segment Reporting Information [Line Items]
Equity in Earnings of Affiliates											(17,574)
Investments in Unconsolidated Equity Affiliates											31,237
Gas Segment [Member]
Segment Reporting Information [Line Items]
Oil and Gas Sales Revenue									793,248	726,921	1,004,924
Gain (Loss) on Hedging Activity									(141,021)	392,942	23,193
Sales Revenue, Services, Other									0	0	0
Sales-Purchased Gas									43,256	14,450	8,999
Freight-Outside									0	0	0
Segment Reporting - Intersegment Transfers									424	1,538	2,458
Total Revenue and Other Income									695,907	1,135,851	1,039,574
Income (Loss) from Continuing Operations before Income Taxes, Domestic									(378,840)	(678,857)	189,714
Total Assets	6,235,568		6,892,284						6,235,568	6,892,284	7,364,185
Depreciation, Depletion and Amortization									417,853	370,374	323,600
Segment Reporting - Capital Expenditures									165,101	832,446	1,103,656
Equity in Earnings of Affiliates									(51,742)	(46,614)	(32,217)
Investments in Unconsolidated Equity Affiliates	188,376		234,803						188,376	234,803	121,721
Other Segments [Member]
Segment Reporting Information [Line Items]
Sales-Outside									0	0	0
Gain (Loss) on Hedging Activity									0	0	0
Sales Revenue, Services, Other									32,038	30,967	276,242
Sales-Purchased Gas									0	0	0
Freight-Outside									0	0	0
Segment Reporting - Intersegment Transfers									0	0	78,229
Total Revenue and Other Income									32,038	30,967	354,471
Income (Loss) from Continuing Operations before Income Taxes, Domestic									(277,399)	(200,304)	(438,073)
Total Assets	966,124		939,497						966,124	939,497	1,186,874
Depreciation, Depletion and Amortization									12,455	19,882	35,727
Segment Reporting - Capital Expenditures									10,910	14,197	14,567
Equity in Earnings of Affiliates									(1,336)	(8,283)
Investments in Unconsolidated Equity Affiliates	2,588		2,527						2,588	2,527
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Sales-Outside									0	0	0
Gain (Loss) on Hedging Activity									0	0	0
Sales Revenue, Services, Other									0	0	0
Sales-Purchased Gas									0	0	0
Freight-Outside									0	0	0
Segment Reporting - Intersegment Transfers									(424)	(1,538)	(80,687)
Total Revenue and Other Income									(424)	(1,538)	(80,687)
Income (Loss) from Continuing Operations before Income Taxes, Domestic									(424)	(1,538)	(2,458)
Total Assets	83		1,021,820						83	1,021,820	1,009,546
Depreciation, Depletion and Amortization									0	0	0
Segment Reporting - Capital Expenditures									0	0	0
PA Operations [Member] | Coal Segment [Member]
Segment Reporting Information [Line Items]
Sales-Outside									1,065,582	1,289,036	1,616,874
Gain (Loss) on Hedging Activity									0	0	0
Sales Revenue, Services, Other									0	0	0
Sales-Purchased Gas									0	0	0
Freight-Outside									46,468	20,499	23,133
Segment Reporting - Intersegment Transfers									0	0	0
Total Revenue and Other Income									1,112,050	1,309,535	1,640,007
Income (Loss) from Continuing Operations before Income Taxes, Domestic									130,708	404,994	430,968
Total Assets	$ 1,982,206		$ 2,076,301						1,982,206	2,076,301	2,094,041
Depreciation, Depletion and Amortization									168,195	176,864	173,316
Segment Reporting - Capital Expenditures									50,809	136,291	341,229
Coalbed Methane | Gas Segment [Member]
Segment Reporting Information [Line Items]
Oil and Gas Sales Revenue									174,323	200,645	340,739
Gain (Loss) on Hedging Activity									52,396	67,281	4,103
Sales Revenue, Services, Other									0	0	0
Sales-Purchased Gas									0	0	0
Freight-Outside									0	0	0
Segment Reporting - Intersegment Transfers									424	1,538	2,458
Total Revenue and Other Income									227,143	269,464	347,300
Income (Loss) from Continuing Operations before Income Taxes, Domestic									37,999	59,662	108,107
Marcellus Shale | Gas Segment [Member]
Segment Reporting Information [Line Items]
Oil and Gas Sales Revenue									414,484	379,453	457,679
Gain (Loss) on Hedging Activity									147,282	100,785	14,764
Sales Revenue, Services, Other									0	0	0
Sales-Purchased Gas									0	0	0
Freight-Outside									0	0	0
Segment Reporting - Intersegment Transfers									0	0	0
Total Revenue and Other Income									561,766	480,238	472,443
Income (Loss) from Continuing Operations before Income Taxes, Domestic									72,141	56,116	171,902
Utica Shale [Member] | Gas Segment [Member]
Segment Reporting Information [Line Items]
Oil and Gas Sales Revenue									163,112	92,223	86,948
Gain (Loss) on Hedging Activity									29,285	6,430	1,247
Sales Revenue, Services, Other									0	0	0
Sales-Purchased Gas									0	0	0
Freight-Outside									0	0	0
Segment Reporting - Intersegment Transfers									0	0	0
Total Revenue and Other Income									192,397	98,653	88,195
Income (Loss) from Continuing Operations before Income Taxes, Domestic									28,390	(19,428)	43,645
Other Gas | Gas Segment [Member]
Segment Reporting Information [Line Items]
Oil and Gas Sales Revenue									41,329	54,600	119,558
Gain (Loss) on Hedging Activity									(369,984)	218,446	3,079
Sales Revenue, Services, Other									0	0	0
Sales-Purchased Gas									43,256	14,450	8,999
Freight-Outside									0	0	0
Segment Reporting - Intersegment Transfers									0	0	0
Total Revenue and Other Income									(285,399)	287,496	131,636
Income (Loss) from Continuing Operations before Income Taxes, Domestic									$ (517,370)	(775,207)	(133,940)
Duke Energy [Member]
Segment Reporting Information [Line Items]
Total Revenue and Other Income										$ 242,020
NJR Energy Services Company [Member]
Segment Reporting Information [Line Items]
Total Revenue and Other Income											$ 295,779