RETIREMENT PLAN AND POST-RETIREMENT BENEFITS, Accumulated Other Comprehensive Income and Accumulated Benefit Obligation in Excess of Plan Assets (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Projected Benefit Obligation	$ 842,045	$ 806,034
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Accumulated Benefit Obligation	813,101	772,846
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	811,480	729,940
Pension Benefits [Member]
Amounts recorded in accumulated other comprehensive income and as regulatory assets for pension plans [Abstract]
Net actuarial (gain)/loss	(238,672)	(263,015)
Prior service (credit)/cost	34,730	24,343
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	203,942	238,672
Regulatory asset for pension plans	(194,936)	(232,717)
Accumulated other comprehensive income, pre-tax, at December 31	9,006	5,955
Amounts to be amortized from regulatory assets for pension plans and accumulated other comprehensive income into net periodic cost [Abstract]
Actuarial (gain)/loss	(13,891)
Prior service (credit)/cost	(2,897)
Other Post-Retirement Benefits [Member]
Amounts recorded in accumulated other comprehensive income and as regulatory assets for pension plans [Abstract]
Net actuarial (gain)/loss	(34,501)	(71,650)
Prior service (credit)/cost	15,141	37,149
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	19,360	34,501
Regulatory asset for pension plans	(19,360)	(34,501)
Accumulated other comprehensive income, pre-tax, at December 31	0	0
Amounts to be amortized from regulatory assets for pension plans and accumulated other comprehensive income into net periodic cost [Abstract]
Actuarial (gain)/loss	(2,924)
Prior service (credit)/cost	$ (3,947)