Business Acquisitions Business Acquisitions (Alaska Energy and Resources Company (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013 MW	Dec. 31, 2012	Dec. 31, 2011
Business Acquisition [Line Items]
Operating revenues	$ 447,676,000	$ 335,875,000	$ 352,048,000	$ 482,906,000	$ 410,528,000	$ 340,632,000	$ 343,585,000	$ 452,257,000	$ 1,618,505,000	$ 1,547,002,000	$ 1,619,780,000
Peak electric usage									80
Alaska Electric Light & Power [Member]
Business Acquisition [Line Items]
Operating revenues										42,000,000
Total Rate Base					111,000,000					111,000,000
Entity Number of Employees	60								60
Number of Customers					16,000					16,000
Alaska Energy Resources Company [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable									170,000,000
Payments to Acquire Businesses, Gross									500,000
Business Combination, Acquisition Related Costs									$ 1,600,000
Minimum [Member] | Alaska Energy Resources Company [Member]
Business Acquisition [Line Items]
Business Combination Equity Consideration Share Price	$ 21.48								$ 21.48
Maximum [Member] | Alaska Energy Resources Company [Member]
Business Acquisition [Line Items]
Business Combination Equity Consideration Share Price	$ 34.30								$ 34.30
AEL&P Hydroelectric Production [Member] | Alaska Electric Light & Power [Member]
Business Acquisition [Line Items]
Evaluated power capacity, megawatts									24.7
Power purchase agreement [Member] | Alaska Electric Light & Power [Member]
Business Acquisition [Line Items]
Evaluated power capacity, megawatts									78
Hydroelectric Production [Member] | Alaska Electric Light & Power [Member]
Business Acquisition [Line Items]
Evaluated power capacity, megawatts									102.7
Fossil Fuel Plant [Member] | Alaska Electric Light & Power [Member]
Business Acquisition [Line Items]
Evaluated power capacity, megawatts									93.9