INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax at Statutory Rate									$ 60,624	$ 37,440	$ 35,727
Increase (Decrease) Resulting from:
State Income Taxes									6,438	3,985	1,960
ESOP Dividend									(1,300)	(1,298)	(1,232)
Amortization of Investment Tax Credits - Utility									0	(149)	(211)
AFUDC									(900)	(1,109)	(1,481)
Investment and Other Tax Credits									(10,706)	(37,503)	(30,661)
Other - Net									(5)	(6)	347
Income Taxes: Continuing Operations	$ 19,266	$ 2,807	$ (7,189)	$ 39,267	$ (1,006)	$ (10,968)	$ (3,279)	$ 16,613	54,151	1,360	4,449
Income Taxes: Discontinued Operations									(133)	(257)	(312)
Total Income Tax Expense									54,018	1,103	4,137
Current:
Federal									0	0	(62)
State									(1,638)	(2,352)	3,052
Total Current									(1,638)	(2,352)	2,990
Deferred:
Federal									44,246	(4,622)	1,707
State									11,543	8,483	(37)
Total Deferred									55,789	3,861	1,670
Investment Tax Credit - Utility									0	(149)	(211)
Income Taxes: Continuing Operations	19,266	$ 2,807	$ (7,189)	39,267	(1,006)	$ (10,968)	$ (3,279)	16,613	54,151	1,360	4,449
Income Taxes: Discontinued Operations									$ (133)	(257)	(312)
Annual amortization rate of investment tax credits									3.00%
Deferred Tax Assets:
Net Operating Loss Carryforward												$ 211,004	$ 195,358
Investment and Other Tax Credits												213,946	200,491
Derivatives / Unrealized Gain												0	5,652
Deferred State Tax												28,833	24,833
Pension & Other Post Retirement Benefits												19,351	29,998
Deferred Revenues												7,669	4,924
Provision for Uncollectibles												5,231	4,200
Other												8,368	6,448
Total Deferred Tax Asset												494,402	471,904
Deferred Tax Liabilities:
Book versus Tax Basis of Property												732,535	675,521
Deferred Gas Costs - Net												2,052	3,998
Derivatives / Unrealized Loss												1,794	0
Environmental Remediation												32,885	19,207
Deferred Regulatory Costs												1,554	566
Budget Billing - Customer Accounts												3,347	830
Deferred Pension & Other Post Retirement Benefits												34,432	42,216
Conservation Incentive Program												11,846	1,132
Equity In Loss Of Affiliated Companies												3,092	9,111
Other												14,414	15,268
Total Deferred Tax Liability												837,951	767,849
Deferred Tax Liability - Net												343,549	295,945
Research and development credits												3,300
Unrecognized tax benefits	1,445			559	559			552	$ 559	552	547	1,445	559	$ 552
Accrued interest and penalties on unrecognized tax benefits												700	$ 700	$ 700
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance (beginning)				$ 559				$ 552	559	552	547
Increase as a result of tax positions taken in prior years									886	7	5
Balance (ending)	$ 1,445				$ 559				$ 1,445	$ 559	$ 552
Federal
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												557,678
Investment Tax Credit Carryforward												209,424
Alternative minimum tax credits												1,200
Federal | 2030
Deferred Tax Liabilities:
Investment Tax Credit Carryforward												11,628
Federal | 2031
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												163,572
Investment Tax Credit Carryforward												25,664
Federal | 2032
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												42,988
Investment Tax Credit Carryforward												32,071
Federal | 2033
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												67,496
Investment Tax Credit Carryforward												45,606
Federal | 2034
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												119,122
Investment Tax Credit Carryforward												37,699
Federal | 2035
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												70,992
Investment Tax Credit Carryforward												45,097
Federal | 2036
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												93,508
Investment Tax Credit Carryforward												11,659
State
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												220,013
State | 2031
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												45,866
State | 2032
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												19,356
State | 2033
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												34,940
State | 2034
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												28,622
State | 2035
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												9,860
State | 2036
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												$ 81,369