Pension and Other Postretirement Plans (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Deferred pension and OPRB costs recovered [Abstract]
Deferred pension and OPRB costs recovered	$ 300,000	$ 700,000
Pension Benefits [Member]
Components of net periodic benefit cost [Line Items]
Service cost	1,823,000	1,540,000
Interest cost	3,154,000	3,080,000
Expected return on assets	(3,818,000)	(3,531,000)
Amortization of:
Prior service cost	108,000	109,000
Actuarial loss	2,006,000	946,000
Net periodic benefit cost	3,273,000	2,144,000
Postretirement Benefits [Member]
Components of net periodic benefit cost [Line Items]
Service cost	647,000	487,000
Interest cost	1,125,000	982,000
Expected return on assets	(435,000)	(396,000)
Amortization of:
Transition obligation	106,000	107,000
Prior service cost	28,000	27,000
Actuarial loss	621,000	111,000
Net periodic benefit cost	$ 2,092,000	$ 1,318,000