Business Acquisitions Business Acquisitions (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended	0 Months Ended		18 Months Ended
	Dec. 31, 2014 D MW	Oct. 01, 2014	Jul. 01, 2014	Dec. 31, 2014	Dec. 31, 2013 employee
Business Acquisition [Line Items]
Peak electric usage	68
Business Combination Number of Trading Days to Price Equity Consideration Share Price	10
Alaska Electric Light & Power [Member]
Business Acquisition [Line Items]
Number of Customers					16,394
Entity Number of Employees	59			59
Alaska Energy Resources Company [Member]
Business Acquisition [Line Items]
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Gross Accounts Receivable			$ 3,928
Business Combination, Acquisition Related Costs				3,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares		1,427	4,500,014
Business Combination Equity Consideration Share Price			$ 32.46
Business Acquisition Contract Price			170,000
Business Acquisition, Share Price		$ 30.71	$ 33.35
Power purchase agreement [Member] | Alaska Electric Light & Power [Member]
Business Acquisition [Line Items]
Evaluated Power Capacity	78
AEL&P Hydroelectric Production [Member] | Alaska Electric Light & Power [Member]
Business Acquisition [Line Items]
Evaluated Power Capacity	24.7
Number of Electric Generating Facilities	4			4
Hydroelectric Production [Member] | Alaska Electric Light & Power [Member]
Business Acquisition [Line Items]
Evaluated Power Capacity	102.7
Fossil Fuel Plant [Member] | Alaska Electric Light & Power [Member]
Business Acquisition [Line Items]
Evaluated Power Capacity	93.9
Acquisition-related Costs [Member] | Alaska Energy Resources Company [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs				$ 400