Pension and Other Postretirement Plans (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Deferred pension and OPRB costs recovered [Abstract]
Deferred pension and OPRB costs recovered	$ 300,000	$ 700,000	$ 600,000	$ 1,300,000
Pension Benefits [Member]
Components of net periodic benefit cost [Line Items]
Service cost	1,920,000	1,514,000	3,743,000	3,054,000
Interest cost	3,321,000	3,030,000	6,475,000	6,110,000
Expected return on assets	(4,021,000)	(3,473,000)	(7,839,000)	(7,004,000)
Amortization of:
Prior service cost	114,000	107,000	222,000	216,000
Actuarial loss	2,112,000	931,000	4,118,000	1,877,000
Net periodic benefit cost	3,446,000	2,109,000	6,719,000	4,253,000
Postretirement Benefits [Member]
Components of net periodic benefit cost [Line Items]
Service cost	606,000	514,000	1,253,000	1,001,000
Interest cost	1,053,000	1,036,000	2,178,000	2,018,000
Expected return on assets	(407,000)	(418,000)	(842,000)	(814,000)
Amortization of:
Transition obligation	99,000	113,000	206,000	219,000
Prior service cost	26,000	29,000	54,000	57,000
Actuarial loss	581,000	117,000	1,201,000	228,000
Net periodic benefit cost	$ 1,958,000	$ 1,391,000	$ 4,050,000	$ 2,709,000