Consolidated Statements of Changes in 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	$ (28,438)
Changes During Year	(2,667)	[1]	(6,626)	[1]	(2,343)	[1]
Balance at December 31	(31,105)		(28,438)
Postretirement Liability Adjustment [Member]
Change In Accumulated Other Comprehensive Loss Balances [Roll Forward]
Balance at January 1	(21,595)	[1]	(15,928)	[1]	(12,626)	[1]
Changes During Year	(1,842)	[1]	(5,667)	[1]	(3,302)	[1]
Balance at December 31	(23,437)	[1]	(21,595)	[1]	(15,928)	[1]
Unrealized Gain (Loss) on Derivatives-Other [Member]
Change In Accumulated Other Comprehensive Loss Balances [Roll Forward]
Balance at January 1	(2,870)	[1]	(2,082)	[1]	(2,331)	[1]
Changes During Year	(92)	[1]	(788)	[1]	249	[1]
Balance at December 31	(2,962)	[1]	(2,870)	[1]	(2,082)	[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]
Other Comprehensive Income (Loss) of Affiliated Companies [Member]
Change In Accumulated Other Comprehensive Loss Balances [Roll Forward]
Balance at January 1	(3,767)	[1]	(3,956)	[1]	(4,327)	[1]
Changes During Year	(1,233)	[1]	189	[1]	371	[1]
Balance at December 31	(5,000)	[1]	(3,767)	[1]	(3,956)	[1]
Accumulated Other Comprehensive Loss [Member]
Change In Accumulated Other Comprehensive Loss Balances [Roll Forward]
Balance at January 1	(28,438)	[1]	(21,812)	[1]	(19,469)	[1]
Changes During Year	(2,667)	[1]	(6,626)	[1]	(2,343)	[1]
Balance at December 31	$ (31,105)	[1]	$ (28,438)	[1]	$ (21,812)	[1]

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