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, 2012	Dec. 31, 2011
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	$ 935,503	$ 842,045
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Accumulated Benefit Obligation	896,988	813,101
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	841,047	811,480
United States Pension Plans of US Entity, Defined Benefit [Member]
Amounts recorded in accumulated other comprehensive income and as regulatory assets for pension plans [Abstract]
Net actuarial (gain)/loss	(203,942)	(238,672)
Prior service (credit)/cost	(60,691)	34,730
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	(264,633)	(203,942)
Regulatory asset for pension plans	(252,114)	(194,936)
Accumulated other comprehensive income, pre-tax, at December 31	(12,519)	(9,006)
Amounts to be amortized from regulatory assets for pension plans and accumulated other comprehensive income into net periodic cost [Abstract]
Actuarial (gain)/loss	19,188
Prior service (credit)/cost	(2,882)
United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member]
Amounts recorded in accumulated other comprehensive income and as regulatory assets for pension plans [Abstract]
Net actuarial (gain)/loss	(19,360)	(34,501)
Prior service (credit)/cost	(9,474)	15,141
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	(28,834)	(19,360)
Regulatory asset for pension plans	(28,834)	(19,360)
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	3,561
Prior service (credit)/cost	$ (3,809)