STATEMENTS OF CHANGES IN COMMON EQUITY AND COMPREHENSIVE INCOME (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Change In Accumulated Other Comprehensive Loss Balances [Roll Forward]
Balance at January 1	$ (12,129)
Changes During Year	(1,156)	[1]	(3,009)	[1]	(2,790)	[1]
Balance at December 31	(13,285)		(12,129)
Postretirement Liability Adjustment [Member]
Change In Accumulated Other Comprehensive Loss Balances [Roll Forward]
Balance at January 1	(11,275)	[1]	(8,599)	[1]	(5,443)	[1]
Changes During Year	(1,683)	[1]	(2,676)	[1]	(3,156)	[1]
Balance at December 31	(12,958)	[1]	(11,275)	[1]	(8,599)	[1]
Unrealized Gain (Loss) on Available-for-Sale Securities [Member]
Change In Accumulated Other Comprehensive Loss Balances [Roll Forward]
Balance at January 1	(206)	[1]	154	[1]	(185)	[1]
Changes During Year	500	[1]	(360)	[1]	339	[1]
Balance at December 31	294	[1]	(206)	[1]	154	[1]
Unrealized (Loss) Gain on Derivatives [Member]
Change In Accumulated Other Comprehensive Loss Balances [Roll Forward]
Balance at January 1	(648)	[1]	(675)	[1]	(702)	[1]
Changes During Year	27	[1]	27	[1]	27	[1]
Balance at December 31	(621)	[1]	(648)	[1]	(675)	[1]
Accumulated Other Comprehensive Loss [Member]
Change In Accumulated Other Comprehensive Loss Balances [Roll Forward]
Balance at January 1	(12,129)	[1]	(9,120)	[1]	(6,330)	[1]
Changes During Year	(1,156)	[1]	(3,009)	[1]	(2,790)	[1]
Balance at December 31	$ (13,285)	[1]	$ (12,129)	[1]	$ (9,120)	[1]

[1] Determined using a combined statutory tax rate of 41%.