Pension and Other Postretirement Plans (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Deferred Pension and OPRB Costs Recovered [Abstract]
Deferred pension and OPRB costs recovered	$ 700,000	$ 700,000	$ 1,300,000	$ 1,300,000
Pension Plans Defined Benefit [Member]
Components of net periodic benefit cost [Line Items]
Service cost	1,514,000	1,403,000	3,054,000	2,937,000
Interest cost	3,030,000	2,781,000	6,110,000	5,822,000
Expected return on assets	(3,473,000)	(2,720,000)	(7,004,000)	(5,694,000)
Amortization of:
Transition obligation	0	0	0	0
Prior service cost	107,000	101,000	216,000	212,000
Actuarial loss	931,000	802,000	1,877,000	1,678,000
Net periodic benefit cost	2,109,000	2,367,000	4,253,000	4,955,000
Other Postretirement Benefit Plans Defined Benefit [Member]
Components of net periodic benefit cost [Line Items]
Service cost	514,000	443,000	1,001,000	926,000
Interest cost	1,036,000	906,000	2,018,000	1,896,000
Expected return on assets	(418,000)	(283,000)	(814,000)	(592,000)
Amortization of:
Transition obligation	113,000	98,000	219,000	205,000
Prior service cost	29,000	25,000	57,000	53,000
Actuarial loss	117,000	101,000	228,000	211,000
Net periodic benefit cost	$ 1,391,000	$ 1,290,000	$ 2,709,000	$ 2,699,000