Benefits 3 (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Pension member
Net Periodic Benefit Cost
Service cost	$ 3,657	$ 3,251	$ 2,778
Interest cost	10,140	10,172	9,955
Expected return on plan assets	(10,653)	(9,348)	(8,577)
Prior service cost (credit) amortization	587	552	552
Actuarial loss (gain) amortization	7,985	8,048	8,405
Net periodic benefit cost subtotal	11,716	12,675	13,113
Regulatory adjustment	868	(4)	54
Net periodic benefit cost	12,584	12,671	13,167
OPEB member
Net Periodic Benefit Cost
Service cost	3,480	3,064	2,970
Interest cost	6,050	5,612	5,481
Expected return on plan assets	(5,820)	(4,918)	(3,123)
Prior service cost (credit) amortization	(1,811)	(1,647)	(1,260)
Actuarial loss (gain) amortization	(1,353)	(1,862)	(847)
Net periodic benefit cost subtotal	546	249	3,221
Regulatory adjustment	2,665	2,665	2,665
Net periodic benefit cost	$ 3,211	$ 2,914	$ 5,886