Regulatory Assets and Liabilities, Regulatory Liabilities (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	$ 83,759		$ 75,891
Regulatory Liability, Noncurrent	81,504		91,815
Plant Removal Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	0		0
Regulatory Liability, Noncurrent	53,006		66,575
Regulatory liability, remaining amortization period	Plant lives
Deferred Electric Energy Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	55,395		61,874
Regulatory Liability, Noncurrent	0		0
Regulatory liability, remaining amortization period	Less than one year
Contract Valuation Adjustments
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	14,243	[1]	4,292	[1]
Regulatory Liability, Noncurrent	6,849	[1]	11,159	[1]
Regulatory liability, remaining amortization period	Term of related contract
Gain From Asset Sales
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	11,172		4,903
Regulatory Liability, Noncurrent	4,201		8,272
Regulatory liability, remaining amortization period	Various
Conservation Programs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	1,465	[2]	1,875	[2]
Regulatory Liability, Noncurrent	0	[2]	0	[2]
Regulatory liability, remaining amortization period	Less than one year
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	1,484		2,947
Regulatory Liability, Noncurrent	$ 17,448		$ 5,809
Regulatory liability, remaining amortization period	Various

[1] Includes the fair value of certain long-term PPAs used to meet energy capacity requirements.

[2] Includes costs for conservation programs as well as incentives allowed in certain jurisdictions.