Cost and Fair Value Basis of Long-Term Debt (tables)

12 Months Ended

Dec. 31, 2011

Long-term Debt Current And Noncurrent Abstract

Schedule of Debt [Table Text Block]

Thousands			2011		2010		2009
Utility Medium-Term Notes:
First Mortgage Bonds:
	4.11 % Series B due 2010	$	-	$	-	$	10,000
	7.45 % Series B due 2010		-		-		25,000
	6.665% Series B due 2011		-		10,000		10,000
	7.13 % Series B due 2012		40,000		40,000		40,000
	8.26 % Series B due 2014		10,000		10,000		10,000
	3.95 % Series B due 2014		50,000		50,000		50,000
	4.70 % Series B due 2015		40,000		40,000		40,000
	5.15 % Series B due 2016		25,000		25,000		25,000
	7.00 % Series B due 2017		40,000		40,000		40,000
	6.60 % Series B due 2018		22,000		22,000		22,000
	8.31 % Series B due 2019		10,000		10,000		10,000
	7.63 % Series B due 2019		20,000		20,000		20,000
	5.37 % Series B due 2020		75,000		75,000		75,000
	9.05 % Series A due 2021		10,000		10,000		10,000
	3.176 % Series A due 2021		50,000		-		-
	5.62 % Series B due 2023		40,000		40,000		40,000
	7.72 % Series B due 2025		20,000		20,000		20,000
	6.52 % Series B due 2025		10,000		10,000		10,000
	7.05 % Series B due 2026		20,000		20,000		20,000
	7.00 % Series B due 2027		20,000		20,000		20,000
	6.65 % Series B due 2027		19,700		19,700		19,700
	6.65 % Series B due 2028		10,000		10,000		10,000
	7.74 % Series B due 2030		20,000		20,000		20,000
	7.85 % Series B due 2030		10,000		10,000		10,000
	5.82 % Series B due 2032		30,000		30,000		30,000
	5.66 % Series B due 2033		40,000		40,000		40,000
	5.25 % Series B due 2035		10,000		10,000		10,000
			641,700		601,700		636,700
Subsidiary Senior Secured Notes:
	Gill Ranch Notes due 2016(1)		40,000		-		-
			681,700		601,700		636,700
	Less current maturities of long-term debt		40,000		10,000		35,000
Total long-term debt		$	641,700	$	591,700	$	601,700

Fair Value Of Long Term Debt Table [Text Block]

		December 31,
Thousands		2011		2010
Carrying amount	$	681,700	$	601,700
Estimated fair value	$	808,724	$	690,126