Pension and Other Postretirement Plans (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Deferred Pension and OPRB Costs Recovered [Abstract]
Deferred pension and OPRB costs recovered	$ 700,000	$ 700,000	$ 2,000,000	$ 2,000,000
Pension Benefits [Member]
Components of net periodic benefit cost [Line Items]
Service cost	1,527,000	1,469,000	4,581,000	4,406,000
Interest cost	3,055,000	2,912,000	9,165,000	8,734,000
Expected return on assets	(3,502,000)	(2,848,000)	(10,507,000)	(8,541,000)
Amortization of:
Transition obligation	0	0	0	0
Prior service cost	108,000	106,000	324,000	318,000
Actuarial loss	939,000	839,000	2,816,000	2,517,000
Net periodic benefit cost	2,127,000	2,478,000	6,379,000	7,434,000
Postretirement Benefits [Member]
Components of net periodic benefit cost [Line Items]
Service cost	500,000	463,000	1,501,000	1,389,000
Interest cost	1,010,000	948,000	3,028,000	2,844,000
Expected return on assets	(407,000)	(296,000)	(1,221,000)	(888,000)
Amortization of:
Transition obligation	110,000	102,000	329,000	307,000
Prior service cost	28,000	27,000	85,000	80,000
Actuarial loss	114,000	106,000	342,000	316,000
Net periodic benefit cost	$ 1,355,000	$ 1,350,000	$ 4,064,000	$ 4,048,000