Pension and Other Postretirement Plans (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Deferred pension and OPRB costs recovered [Abstract]
Deferred pension and OPRB costs recovered	$ 300,000	$ 300,000	$ 900,000	$ 900,000
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	1,924,000	1,871,000	5,764,000	5,613,000
Interest cost	3,178,000	3,236,000	9,521,000	9,711,000
Expected return on assets	(4,764,000)	(3,917,000)	(14,273,000)	(11,756,000)
Amortization of:
Prior service cost	79,000	111,000	237,000	333,000
Actuarial loss	2,011,000	2,058,000	6,023,000	6,177,000
Net periodic benefit cost	2,428,000	3,359,000	7,272,000	10,078,000
Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	594,000	626,000	1,781,000	1,879,000
Interest cost	966,000	1,089,000	2,898,000	3,267,000
Expected return on assets	(542,000)	(421,000)	(1,626,000)	(1,263,000)
Amortization of:
Transition obligation	0	103,000	2,000	309,000
Prior service cost	28,000	27,000	83,000	81,000
Actuarial loss	310,000	601,000	930,000	1,802,000
Net periodic benefit cost	$ 1,356,000	$ 2,025,000	$ 4,068,000	$ 6,075,000