RETIREMENT BENEFITS (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
RETIREMENT BENEFITS
Number of non-callable corporate bonds (in Counts)	500
Amounts recognized in the balance sheet
Accounts payable and accrued liabilities	$ 59,307,000	$ 58,820,000
Pension and other postretirement benefit obligations	103,371,000	93,405,000
Maximum
Retirement benefits
Maturity of non-callable corporate bonds (in years)	30
Minimum
Retirement benefits
Maturity of non-callable corporate bonds (in years)	0
Pensions
Retirement benefits
Increase in net liability	7,600,000	4,500,000
Estimated contribution in next fiscal year	11,100,000
Reconciliation of Projected Benefit Obligations:
Benefit obligation at beginning of year	186,840,000	169,055,000
Service cost	5,596,000	4,887,000	4,612,000
Interest cost	10,405,000	10,115,000	9,876,000
Net actuarial (gain)/loss	20,869,000	10,946,000
Benefits and expenses paid	(8,622,000)	(8,163,000)
Benefit obligation at end of year	215,088,000	186,840,000	169,055,000
Reconciliation of Fair Value of Plan Assets:
Fair value of plan assets at beginning of year	120,353,000	107,076,000
Actual return on plan assets gain/(loss)	(625,000)	11,740,000
Employer contribution	29,869,000	9,700,000
Benefits paid	(8,622,000)	(8,163,000)
Fair value of plan assets at end of year	140,975,000	120,353,000	107,076,000
Reconciliation of Funded Status:
Fair value of plan assets	140,975,000	120,353,000	107,076,000
Projected benefit obligations	(215,088,000)	(186,840,000)	(169,055,000)
Funded status	(74,113,000)	(66,487,000)
Employee pension plan accumulated benefit obligation
Accumulated benefit obligation	191,295,000	164,340,000
Amounts recognized in the balance sheet
Pension and other postretirement benefit obligations	74,113,000	66,487,000
Net Periodic Pension Benefit Cost:
Service cost	5,596,000	4,887,000	4,612,000
Interest cost	10,405,000	10,115,000	9,876,000
Expected return on plan assets	(11,139,000)	(9,847,000)	(10,379,000)
Amortization of prior service cost	532,000	531,000	604,000
Amortization of Actuarial Loss	5,494,000	3,996,000	3,182,000
Net periodic benefit cost	10,888,000	9,682,000	7,895,000
Activity in the regulatory asset accounts
Beginning Balance	67,050,000
Current Year Actuarial Loss	32,632,000
Amortization of Actuarial Loss	(5,494,000)
Amortization of Prior Service (Cost)/Credit	(532,000)
Ending Balance	93,656,000	67,050,000
Amount of net actuarial gains / losses, transition obligations / assets and prior period service costs in regulatory assets not yet recognized as a component of net periodic benefit cost
Net actuarial loss	91,144,000
Prior service cost (benefit)	2,512,000
Total	93,656,000	67,050,000
Amounts expected to be recognized in the subsequent year
Net actuarial loss	7,799,000
Prior service cost (benefit)	532,000
Total	8,331,000
Weighted-average assumptions used to determine the benefit obligation
Discount rate (as a percent)	4.70%	5.50%
Rate of compensation increase (as a percent)	3.50%	4.50%
Weighted-average assumptions used to determine the net benefit cost (income)
Discount rate (as a percent)	5.50%	6.00%	6.30%
Expected return on plan assets (as a percent)	8.00%	8.00%	8.50%
Rate of compensation increase (as a percent)	4.50%	4.50%	4.50%
Pensions | Payments from Trust
Expected benefit payments
2012	8,400,000
2013	9,000,000
2014	9,700,000
2015	10,400,000
2016	11,100,000
2017 - 2021	65,900,000
Pensions | Payments from Company Funds
Expected benefit payments
2012	300,000
2013	300,000
2014	300,000
2015	300,000
2016	300,000
2017 - 2021	1,900,000
OPEB
Retirement benefits
Increase in net liability	600,000	4,300,000
Estimated contribution in next fiscal year	3,200,000
Estimated benefit payments
Eligible age (in years)	55
Minimum service period for eligibility (in years)	5
Reconciliation of Projected Benefit Obligations:
Benefit obligation at beginning of year	80,938,000	69,911,000
Service cost	2,266,000	2,138,000	1,830,000
Interest cost	4,383,000	4,329,000	3,907,000
Net actuarial (gain)/loss	(2,136,000)	6,454,000
Plan participant's contribution	863,000	949,000
Benefits and expenses paid	(3,261,000)	(2,966,000)
Federal subsidy	173,000	123,000
Benefit obligation at end of year	83,226,000	80,938,000	69,911,000
Reconciliation of Fair Value of Plan Assets:
Fair value of plan assets at beginning of year	56,730,000	50,036,000
Actual return on plan assets gain/(loss)	279,000	4,825,000
Employer contribution	3,544,000	3,681,000
Benefits paid	(3,160,000)	(2,845,000)
Plan participant's contribution	826,000	917,000
Federal subsidy	165,000	116,000
Fair value of plan assets at end of year	58,384,000	56,730,000	50,036,000
Reconciliation of Funded Status:
Fair value of plan assets	58,384,000	56,730,000	50,036,000
Projected benefit obligations	(83,226,000)	(80,938,000)	(69,911,000)
Funded status	(24,842,000)	(24,208,000)
Amounts recognized in the balance sheet
Accounts payable and accrued liabilities	136,000	121,000
Pension and other postretirement benefit obligations	24,706,000	24,087,000
Net Periodic Pension Benefit Cost:
Service cost	2,266,000	2,138,000	1,830,000
Interest cost	4,383,000	4,329,000	3,907,000
Expected return on plan assets	(4,157,000)	(3,844,000)	(3,843,000)
Amortization of prior service cost	(1,011,000)	(1,011,000)	(1,011,000)
Amortization of Actuarial Loss	1,762,000	1,499,000	869,000
Net periodic benefit cost	3,243,000	3,111,000	1,752,000
Activity in the regulatory asset accounts
Beginning Balance	16,031,000
Current Year Actuarial Loss	1,740,000
Amortization of Actuarial Loss	(1,762,000)
Amortization of Prior Service (Cost)/Credit	1,011,000
Ending Balance	17,020,000	16,031,000
Amount of net actuarial gains / losses, transition obligations / assets and prior period service costs in regulatory assets not yet recognized as a component of net periodic benefit cost
Net actuarial loss	22,637,000
Prior service cost (benefit)	(5,617,000)
Total	17,020,000	16,031,000
Amounts expected to be recognized in the subsequent year
Net actuarial loss	1,871,000
Prior service cost (benefit)	(1,011,000)
Total	860,000
Weighted-average assumptions used to determine the benefit obligation
Discount rate (as a percent)	4.90%	5.50%
Rate of compensation increase (as a percent)	3.50%	4.50%
Weighted-average assumptions used to determine the net benefit cost (income)
Discount rate (as a percent)	5.50%	6.00%	6.30%
Expected return on plan assets (as a percent)	7.00%	7.00%	7.45%
Rate of compensation increase (as a percent)	4.50%	4.50%	4.50%
Cost trend rate used to measure the expected cost of healthcare benefits and benefit obligation
Cost trend rate assumed (as a percent)	8.00%
Decrease in trend rate through 2018 (as a percent)	0.50%
Ultimate rate (as a percent)	5.00%
Effect of 1% change in assumed healthcare cost growth rates
Effect of 1% increase on total of service and interest cost	1,258,000
Effect of 1% decrease on total of service and interest cost	(990,000)
Effect of 1% increase on post-retirement benefit obligation	12,663,000
Effect of 1% decrease on post-retirement benefit obligation	(10,235,000)
OPEB | Payments from Trust
Expected benefit payments
2012	2,300,000
2013	2,600,000
2014	2,900,000
2015	3,100,000
2016	3,500,000
2017 - 2021	21,300,000
OPEB | Expected Federal Subsidy
Estimated benefit payments
2012	300,000
2013	300,000
2014	400,000
2015	400,000
2016	500,000
2017 - 2021	3,100,000
OPEB | Payments from Company Funds
Expected benefit payments
2012	100,000
2013	100,000
2014	100,000
2015	100,000
2016	200,000
2017 - 2021	900,000
SERP
Reconciliation of Projected Benefit Obligations:
Benefit obligation at beginning of year	2,895,000	2,575,000
Service cost	93,000	70,000	61,000
Interest cost	183,000	153,000	148,000
Net actuarial (gain)/loss	1,883,000	160,000
Benefits and expenses paid	(191,000)	(63,000)
Benefit obligation at end of year	4,863,000	2,895,000	2,575,000
Reconciliation of Funded Status:
Projected benefit obligations	(4,863,000)	(2,895,000)	(2,575,000)
Funded status	(4,863,000)	(2,895,000)
Employee pension plan accumulated benefit obligation
Accumulated benefit obligation	4,670,000	2,431,000
Amounts recognized in the balance sheet
Accounts payable and accrued liabilities	311,000	64,000
Pension and other postretirement benefit obligations	4,552,000	2,831,000
Net Periodic Pension Benefit Cost:
Service cost	93,000	70,000	61,000
Interest cost	183,000	153,000	148,000
Amortization of prior service cost	(8,000)	(8,000)	(8,000)
Amortization of Actuarial Loss	171,000	96,000	103,000
Net periodic benefit cost	439,000	311,000	304,000
Activity in the regulatory asset accounts
Beginning Balance	1,291,000
Current Year Actuarial Loss	1,884,000
Amortization of Actuarial Loss	(171,000)
Amortization of Prior Service (Cost)/Credit	8,000
Ending Balance	3,012,000	1,291,000
Amount of net actuarial gains / losses, transition obligations / assets and prior period service costs in regulatory assets not yet recognized as a component of net periodic benefit cost
Net actuarial loss	3,051,000
Prior service cost (benefit)	(39,000)
Total	3,012,000	1,291,000
Amounts expected to be recognized in the subsequent year
Net actuarial loss	305,000
Prior service cost (benefit)	(8,000)
Total	$ 297,000