INCOME TAXES (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current
Federal	$ (16,626,000)	$ (21,059,000)	$ 35,452,000
State	(3,951,000)	(547,000)	4,331,000
Total current	(20,577,000)	(21,606,000)	39,783,000
Deferred
Federal	72,840,000	56,484,000	(1,835,000)
State	10,433,000	558,000	(4,706,000)
Total deferred	83,273,000	57,042,000	(6,541,000)
Investment tax credits	(195,000)	(152,000)	(146,000)
Total income tax expense	62,501,000	35,284,000	33,096,000
Components of the deferred income tax provision:
Property related (accelerated depreciation and other)	43,734,000	76,168,000	10,289,000
Investment in GenConn	32,694,000	19,201,000	132,000
Pension benefits	11,653,000	(11,182,000)	(5,941,000)
Storm costs	8,922,000	2,358,000	184,000
Regulatory deferrals	6,570,000	(19,213,000)	(5,278,000)
Corporate acquisition costs	6,260,000	(9,206,000)	0
Goodwill	4,668,000	588,000	0
Conservation adjustment mechanisms-Gas Companies	864,000	418,000	0
Bond redemption costs	(340,000)	(340,000)	(340,000)
Incentive compensation plans	(620,000)	268,000	(634,000)
Deferred gas costs	(1,608,000)	4,216,000	0
Post retirement benefits	(2,117,000)	(2,271,000)	(2,870,000)
Seabrook lease buyout	(2,985,000)	(2,542,000)	(1,367,000)
Net operating loss carry forward	(23,300,000)	0	0
Other, net	(1,122,000)	(1,421,000)	(716,000)
Total deferred	83,273,000	57,042,000	(6,541,000)
Reconciliation of federal statutory rate to effective tax rate
Computed tax at federal statutory rate	56,774,000	31,549,000	30,595,000
Investment tax credits	(195,000)	(152,000)	(146,000)
Allowance for equity funds used during construction	(3,689,000)	(2,511,000)	(227,000)
Amortization of nuclear plant regulatory assets	8,885,000	7,661,000	3,696,000
Book depreciation more (less) than non-normalized tax depreciation	(1,023,000)	(734,000)	313,000
State income taxes, net of federal income tax benefits	4,214,000	7,000	(223,000)
ESOP dividend payments	(526,000)	(488,000)	(457,000)
Mark-to-market adjustments to non-qualified pension investments	3,000	(208,000)	(391,000)
Uncollectible reserve and programs	1,477,000	159,000	0
Acquisition and closing related expenses	6,000	967,000	0
Other items, net	(3,425,000)	(966,000)	(64,000)
Total income tax expense	62,501,000	35,284,000	33,096,000
Book income before income taxes	162,211,000	90,141,000	87,413,000
Effective income tax rates	38.50%	39.10%	37.90%
Net operating loss for federal taxes	100,000,000
Effect of accelerated capital recovery		40,500,000
Interest income	500,000
Changes gross income tax reserves [Roll Forward]
Balance, beginning balance	11,349,000	0
Increases for tax positions related to prior years	0	8,922,000
Increases for tax positions related to current year	2,327,000	2,427,000
Balance as of December 31,	13,676,000	11,349,000	0
Non-current deferred tax liabilities for taxable temporary differences	512,700,000
Non-current deferred tax assets for deductible temporary differences	124,100,000
Non-current deferred tax liability	388,600,000
Current deferred tax assets	41,635,000	24,039,000
Deferred income tax assets:
Regulatory asset related to pension and other post-retirement benefits	83,057,000	78,427,000
Post-retirement benefits	69,624,000	12,106,000
Net operating loss carry forward	23,300,000
Regulatory deferrals	4,751,000	10,966,000
Acquisition and closing related expenses	2,947,000	9,207,000
ASC 740 gross-up effect on deferred taxes	3,531,000	6,477,000
Deferred gas company costs	0	3,637,000
Connecticut Yankee equity investment	3,145,000	3,145,000
Long-term incentive plan	4,622,000	3,498,000
Vacation accrual	2,927,000	2,728,000
Incentive compensation plans	2,895,000	2,275,000
Deferred compensation plan	2,708,000	2,171,000
Supplemental pensions	2,354,000	2,134,000
Stock compensation plans	2,037,000	1,836,000
Uncollectibles	1,359,000	1,439,000
Post-employment benefits	615,000	700,000
Gains on sale of property	662,000	662,000
Interest during construction	360,000	442,000
Other	11,166,000	12,449,000
Total deferred tax assets	222,060,000	154,299,000
Deferred income tax liabilities:
Plant basis differences	169,890,000	182,797,000
Accelerated depreciation timing differences	220,030,000	154,067,000
Regulatory asset related to pension and other post-retirement benefits	71,325,000	69,358,000
Investment in GenConn	52,027,000	19,332,000
Seabrook lease buyout	13,656,000	16,641,000
Hardship programs	5,037,000	5,889,000
Bond redemption costs	5,446,000	5,786,000
Other	31,567,000	30,554,000
Total deferred tax liabilities	568,978,000	484,424,000
Deferred income taxes	388,553,000	354,164,000
Deferred income taxes - net	346,918,000	330,125,000
Assets:
Deferred and refundable income taxes	41,635,000	24,039,000
Liabilities:
Plant basis differences	169,890,000	182,797,000
Accelerated depreciation timing differences	220,030,000	154,067,000
Regulatory asset related to pension and other post-retirement benefits	71,325,000	69,358,000
Investment in GenConn	52,027,000	19,332,000
Seabrook lease buyout	13,656,000	16,641,000
Hardship programs	5,037,000	5,889,000
Bond redemption costs	5,446,000	5,786,000
Other	31,567,000	30,554,000
Total deferred tax liabilities	568,978,000	484,424,000
Deferred income taxes	388,553,000	354,164,000
Deferred income taxes - net	$ 346,918,000	$ 330,125,000