Pension Plans and Other Postretirement Benefits (Details-5) (USD $)	12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jan. 31, 2012	Dec. 31, 2012 Pension Benefits [Member]	Dec. 31, 2011 Pension Benefits [Member]	Dec. 31, 2010 Pension Benefits [Member]	Dec. 31, 2009 Pension Benefits [Member]	Dec. 31, 2012 Postretirement Benefits [Member]	Dec. 31, 2011 Postretirement Benefits [Member]	Dec. 31, 2010 Postretirement Benefits [Member]	Dec. 31, 2009 Postretirement Benefits [Member]	Dec. 31, 2011 Gross Postretirement Benefits [Member]	Dec. 31, 2011 Expected Medicare Part D Subsidy [Member]
Amounts recognized as regulatory asset [Abstract]
Net actuarial loss						$ 110,989,000	$ 63,008,000			$ 34,928,000	$ 12,131,000
Prior service cost						1,447,000	1,880,000			640,000	750,000
Transition obligation						0	0			463,000	890,000
Total	148,500,000	78,700,000				112,436,000	64,888,000			36,031,000	13,771,000
Projected benefit obligation in excess of plan assets [Abstract]
Projected benefit obligation, end of year						283,668,000	232,900,000
Accumulated benefit obligation, end of year						245,918,000	200,946,000
Fair value of plan assets						173,311,000	159,354,000	133,871,000		23,456,000	20,949,000	17,338,000
Expected defined benefit plan contributions [Abstract]
Expected contributions for next year	$22 million
Contributions made in January 2012.				20,000,000
Expected future contributions	$11 million to $13 million each year
Cash contributions to pension and other postretirement plans	23,670,000	16,901,000	15,278,000
Defined benefit plan expected future benefit payments in year one						9,721,000				2,682,000			2,881,000	(199,000)
Defined benefit plan expected future benefit payments in year two						10,423,000				2,969,000			3,197,000	(228,000)
Defined benefit plan expected future benefit payments in year three						11,172,000				3,201,000			3,462,000	(261,000)
Defined benefit plan expected future benefit payments in year four						12,014,000				3,454,000			3,752,000	(298,000)
Defined benefit plan expected future benefit payments in year five						12,758,000				3,806,000			4,140,000	(334,000)
Defined benefit plan expected future benefit payments in five fiscal years thereafter						78,493,000				25,918,000			28,124,000	(2,206,000)
Components of net periodic benefit cost [Abstract]
Service cost						6,013,000	5,554,000	5,235,000		1,920,000	1,849,000	1,783,000
Interest cost						12,281,000	11,928,000	11,430,000		3,980,000	3,926,000	3,801,000
Expected return on assets						(14,034,000)	(11,530,000)	(9,016,000)		(1,584,000)	(1,317,000)	(1,005,000)
Special termination benefits						13,000	0	0		0	0	0
Amortization of:
Transition obligation						0	0	143,000		427,000	427,000	427,000
Prior service cost						433,000	437,000	440,000		110,000	110,000	130,000
Actuarial loss						3,771,000	3,401,000	4,748,000		566,000	403,000	581,000
Net periodic benefit cost						8,477,000	9,790,000	12,980,000		5,419,000	5,398,000	5,717,000
Discount rate						5.36%	5.87%	6.11%		5.42%	5.92%	6.11%
Long-term rate of return					8.10%	8.25%	8.50%	8.50%	7.26%	7.39%	7.44%	7.11%
Rate of compensation increase						4.59%	4.59%	4.58%
How 1% increase or decrease in health care cost trends could impact postretirement benefits [Abstract]
1% increase	1,018,000
1% decrease	(819,000)
Deferred Pension and OPRB Costs Recovered [Abstract]
Deferred pension and OPRB costs recovered	$ 2,600,000	$ 2,600,000