Pension and Other Postretirement Plans (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Deferred pension and OPRB costs recovered [Abstract]
Deferred pension and OPRB costs recovered	$ 300,000	$ 700,000	$ 900,000	$ 2,000,000
Pension Benefits [Member]
Components of net periodic benefit cost [Line Items]
Service cost	1,871,000	1,527,000	5,613,000	4,581,000
Interest cost	3,236,000	3,055,000	9,711,000	9,165,000
Expected return on assets	(3,917,000)	(3,502,000)	(11,756,000)	(10,507,000)
Amortization of:
Prior service cost	111,000	108,000	333,000	324,000
Actuarial loss	2,058,000	939,000	6,177,000	2,816,000
Net periodic benefit cost	3,359,000	2,127,000	10,078,000	6,379,000
Postretirement Benefits [Member]
Components of net periodic benefit cost [Line Items]
Service cost	626,000	500,000	1,879,000	1,501,000
Interest cost	1,089,000	1,010,000	3,267,000	3,028,000
Expected return on assets	(421,000)	(407,000)	(1,263,000)	(1,221,000)
Amortization of:
Transition obligation	103,000	110,000	309,000	329,000
Prior service cost	27,000	28,000	81,000	85,000
Actuarial loss	601,000	114,000	1,802,000	342,000
Net periodic benefit cost	$ 2,025,000	$ 1,355,000	$ 6,075,000	$ 4,064,000