Pension Plans and Other Postretirement Benefits (Details-5) (USD $)	12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jan. 31, 2013	Dec. 31, 2013 Pension Benefits [Member]	Dec. 31, 2012 Pension Benefits [Member]	Dec. 31, 2011 Pension Benefits [Member]	Dec. 31, 2010 Pension Benefits [Member]	Dec. 31, 2013 Postretirement Benefits [Member]	Dec. 31, 2012 Postretirement Benefits [Member]	Dec. 31, 2011 Postretirement Benefits [Member]	Dec. 31, 2010 Postretirement Benefits [Member]	Dec. 31, 2012 Gross Postretirement Benefits [Member]	Dec. 31, 2012 Expected Medicare Part D Subsidy [Member]
Amounts recognized as regulatory asset [Abstract]
Net actuarial loss						$ 112,637,000	$ 110,989,000			$ 21,529,000	$ 34,928,000
Prior service cost						105,000	1,447,000			530,000	640,000
Transition obligation						0	0			38,000	463,000
Total	134,800,000	148,500,000				112,742,000	112,436,000			22,097,000	36,031,000
Projected benefit obligation in excess of plan assets [Abstract]
Projected benefit obligation, end of year						315,505,000	283,668,000
Accumulated benefit obligation, end of year						272,462,000	245,918,000
Fair value of plan assets						212,277,000	173,311,000	159,354,000		32,124,000	23,456,000	20,949,000
Expected defined benefit plan contributions [Abstract]
Expected contributions for next year	$32 million
Contributions made in next fiscal year.				30,000,000
Expected future contributions	$11 million to $13 million each year
Cash contributions to pension and other postretirement plans	28,857,000	23,670,000	16,901,000
Defined benefit plan expected future benefit payments in year one						10,722,000				2,617,000			2,796,000	(179,000)
Defined benefit plan expected future benefit payments in year two						11,498,000				2,802,000			3,007,000	(205,000)
Defined benefit plan expected future benefit payments in year three						12,327,000				2,999,000			3,234,000	(235,000)
Defined benefit plan expected future benefit payments in year four						13,022,000				3,275,000			3,537,000	(262,000)
Defined benefit plan expected future benefit payments in year five						13,896,000				3,734,000			4,018,000	(284,000)
Defined benefit plan expected future benefit payments in five fiscal years thereafter						84,834,000				24,564,000			26,425,000	(1,861,000)
Components of net periodic benefit cost [Abstract]
Service cost						7,139,000	6,013,000	5,554,000		2,528,000	1,920,000	1,849,000
Interest cost						12,704,000	12,281,000	11,928,000		4,431,000	3,980,000	3,926,000
Expected return on assets						(15,182,000)	(14,034,000)	(11,530,000)		(1,741,000)	(1,584,000)	(1,317,000)
Special termination benefits						0	13,000	0		0	0	0
Amortization of:
Transition obligation						0	0	0		425,000	427,000	427,000
Prior service cost						430,000	433,000	437,000		110,000	110,000	110,000
Actuarial loss						8,288,000	3,771,000	3,401,000		2,346,000	566,000	403,000
Net periodic benefit cost						13,379,000	8,477,000	9,790,000		8,099,000	5,419,000	5,398,000
Discount rate						4.50%	5.36%	5.87%		4.55%	5.42%	5.92%
Long-term rate of return					8.10%	8.10%	8.25%	8.50%	6.79%	7.26%	7.39%	7.44%
Rate of compensation increase						4.59%	4.59%	4.59%
How 1% increase or decrease in health care cost trends could impact postretirement benefits [Abstract]
1% increase	1,261,000
1% decrease	(1,003,000)
Deferred Pension and OPRB Costs Recovered [Abstract]
Deferred pension and OPRB costs recovered	$ 1,200,000	$ 2,600,000