INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax at Statutory Rate									$ 37,440	$ 35,727	$ 22,181
Increase (Decrease) Resulting from:
State Income Taxes									3,985	1,960	971
ESOP Dividend									(1,298)	(1,232)	(1,176)
Amortization of Investment Tax Credits - Utility									(149)	(211)	(258)
AFUDC									(1,109)	(1,481)	(916)
Investment and Other Tax Credits									(37,503)	(30,661)	(38,179)
Other - Net									(6)	347	(1,637)
Income Taxes: Continuing Operations	$ (1,006)	$ (10,968)	$ (3,279)	$ 16,613	$ 10,415	$ (8,325)	$ (9,510)	$ 11,869	1,360	4,449	(19,014)
Income Taxes: Discontinued Operations									(257)	(312)	(426)
Total Income Tax Expense (Benefit)									1,103	4,137	(19,440)
Current:
Federal									0	(62)	(273)
State									(2,352)	3,052	3,066
Total Current									(2,352)	2,990	2,793
Deferred:
Federal									(4,622)	1,707	(19,978)
State									8,483	(37)	(1,571)
Total Deferred									3,861	1,670	(21,549)
Investment Tax Credit - Utility									(149)	(211)	(258)
Income Taxes: Continuing Operations	(1,006)	$ (10,968)	$ (3,279)	16,613	10,415	$ (8,325)	$ (9,510)	11,869	1,360	4,449	(19,014)
Income Taxes: Discontinued Operations									$ (257)	(312)	(426)
Annual amortization rate of investment tax credits									3.00%
Deferred Tax Assets:
Net Operating Loss Carryforward	195,358				157,174				$ 195,358	157,174
Investment and Other Tax Credits	200,491				154,805				200,491	154,805
Derivatives / Unrealized Gain	5,652				12,554				5,652	12,554
Conservation Incentive Program	0				2,027				0	2,027
Deferred State Tax	24,833				21,548				24,833	21,548
Investment Tax Credit Basis Gross-Up	0				77				0	77
Pension & Other Post Retirement Benefits	29,998				34,892				29,998	34,892
Deferred Revenues	4,924				11,647				4,924	11,647
Provision for Uncollectibles	4,200				6,296				4,200	6,296
Other	6,448				6,734				6,448	6,734
Total Deferred Tax Asset	471,904				407,754				471,904	407,754
Deferred Tax Liabilities:
Book versus Tax Basis of Property	675,521				558,960				675,521	558,960
Deferred Gas Costs - Net	3,998				22,959				3,998	22,959
Environmental Remediation	19,207				12,147				19,207	12,147
Deferred Regulatory Costs	566				6,333				566	6,333
Budget Billing - Customer Accounts	830				1,138				830	1,138
Deferred Pension & Other Post Retirement Benefits	42,216				39,891				42,216	39,891
Conservation Incentive Program	1,132				0				1,132	0
Equity In Loss Of Affiliated Companies	9,111				39,230				9,111	39,230
Other	15,268				13,868				15,268	13,868
Total Deferred Tax Liability	767,849				694,526				767,849	694,526
Current Deferred Tax Asset	0				57,748				0	57,748
Noncurrent Deferred Tax Liability	295,945				344,520				295,945	344,520
Deferred Tax Liability - Net	295,945				286,772				295,945	286,772
Research and development credits	1,400								1,400
Accrued interest and penalties on unrecognized tax benefits	700				700				700	700	600
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at January 1,				$ 552				$ 547	552	547	503
Increase as a result of tax positions taken in prior years									7	5	44
Decrease due to a lapse in the statute of limitations									0	0	0
Settlements									0	0	0
Balance at December 31,	559				$ 552				559	$ 552	$ 547
Federal [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	527,407								527,407
Tax credit carryforwards	197,766								197,766
Alternative minimum tax credits	1,200								1,200
Federal [Member] | 2030 [Member]
Deferred Tax Liabilities:
Tax credit carryforwards	11,628								11,628
Federal [Member] | 2031 [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	163,880								163,880
Tax credit carryforwards	26,613								26,613
Federal [Member] | 2032 [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	43,724								43,724
Tax credit carryforwards	32,071								32,071
Federal [Member] | 2033 [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	68,696								68,696
Tax credit carryforwards	46,179								46,179
Federal [Member] | 2034 [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	117,325								117,325
Tax credit carryforwards	38,727								38,727
Federal [Member] | 2035 [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	133,782								133,782
Tax credit carryforwards	42,548								42,548
State and Local Jurisdiction [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	150,469								150,469
State and Local Jurisdiction [Member] | 2031 [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	45,866								45,866
State and Local Jurisdiction [Member] | 2032 [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	19,356								19,356
State and Local Jurisdiction [Member] | 2033 [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	34,940								34,940
State and Local Jurisdiction [Member] | 2034 [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	28,622								28,622
State and Local Jurisdiction [Member] | 2035 [Member]
Deferred Tax Liabilities:
Operating loss carryforwards	$ 21,685								$ 21,685