Pension Plans and Other Postretirement Benefits (Details-4) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Unfunded status of the plans in balance sheet [Abstract]
Current liability		$ 900,000	$ 800,000
Long-term liability		183,622,000	123,648,000
Regulatory asset		148,500,000	78,700,000
Pension Benefits [Member]
Other postretirement benefits [Abstract]
Fair value of plan assets		173,311,000	159,354,000	133,871,000
Long-term rate of return	8.10%	8.25%	8.50%	8.50%
Funded status [Abstract]
Fair value of plan assets		173,311,000	159,354,000	133,871,000
Benefit obligations		283,668,000	232,900,000	208,780,000
Funded status		(110,357,000)	(73,546,000)
Unfunded status of the plans in balance sheet [Abstract]
Regulatory asset		112,436,000	64,888,000
Postretirement Benefits [Member]
Other postretirement benefits [Abstract]
Fair value of plan assets		23,456,000	20,949,000	17,338,000
Long-term rate of return	7.26%	7.39%	7.44%	7.11%
Fair value of plan assets in master pension trust		20,100,000	17,900,000
Funded status [Abstract]
Fair value of plan assets		23,456,000	20,949,000	17,338,000
Benefit obligations		97,644,000	71,762,000	66,138,000
Funded status		(74,188,000)	(50,813,000)
Unfunded status of the plans in balance sheet [Abstract]
Regulatory asset		$ 36,031,000	$ 13,771,000