Fair Value Measurements Fair Value Recurring Basis (Details) (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Estimate of Fair Value, Fair Value Disclosure [Member]		Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Estimate of Fair Value, Fair Value Disclosure [Member]		Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member]		Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member]		Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member]		Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member]		Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]		Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]		Sep. 30, 2011 Fair Value, Measurements, Recurring [Member] Netting and Collateral [Member]		Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring 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		11,213		12,297		11,213		12,297		0		0		0		0		0		0
Rabbi Trust Investments		7,003		5,495		7,003		5,495		0		0		0		0		0		0
Derivative Asset				1,620	[1]			0	[1]			1,620	[1]			0	[1]			0	[1]
Derivative Liability		(20,057)	[1]	(31,332)	[1]	0	[1]	0	[1]	(20,057)	[1]	(31,332)	[1]	0	[1]	0	[1]	0	[1]	0	[1]
Net derivative liability				(29,712)				0				(29,712)				0				0
Total		$ (1,841)		$ (11,920)		$ 18,216		$ 17,792		$ (20,057)		$ (29,712)		$ 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.