Fair Value Measurements Fair Value Recurring Basis (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Total Net Fair Value [Member]		Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Total Net Fair Value [Member]		Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member]		Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member]		Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Significant Other Observable Inputs(Level 2) [Member]		Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Significant Other Observable Inputs(Level 2) [Member]		Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Significant Unobservable Inputs(Level 3) [Member]		Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Significant Unobservable Inputs(Level 3) [Member]		Mar. 31, 2012 Fair Value, Measurements, Recurring [Member] Margin Cash Collateral Offset [Member]		Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Margin Cash Collateral Offset [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value, level 1 to level 2 transfers, amount	$ 0
Fair value, level 2 to level 1 transfers, amount	0
Restricted cash		8,645,000		12,292,000		8,645,000		12,292,000		0		0		0		0		0		0
Rabbi trust investments		10,017,000		8,049,000		10,017,000		8,049,000		0		0		0		0		0		0
Derivative liability (1)		(19,056,000)	[1]	(20,312,000)	[1]	0	[1]	0	[1]	(19,056,000)	[1]	(20,312,000)	[1]	0	[1]	0	[1]	0	[1]	0	[1]
Net derivative liability				(20,312,000)				0				(20,312,000)				0				0
Total		$ (394,000)		$ 29,000		$ 18,662,000		$ 20,341,000		$ (19,056,000)		$ (20,312,000)		$ 0		$ 0		$ 0		$ 0

[1] The changes in the fair value of these derivatives are deferred as a regulatory asset or liability until the contracts are settled. Upon settlement, associated proceeds or costs are passed through the applicable cost tracking mechanism to customers.