Commitments And Contingencies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 item
Number of collective bargaining agreements with IBEW	3
Percentage of employees belonging to unions	70.00%
Expiration date of collective bargaining agreements	Jun. 30, 2017
Percentage of fuel supply needs filled by contracts, through 2014	100.00%
Percentage of fuel supply needs filled by contracts, in 2015	70.00%
Percentage of fuel supply needs filled by contracts, in 2016	40.00%
Chugach and ML&P Electricity Generation Plant [Member]
Base capacity of power plant	200
Number of generating units	4
Percentage ownership in natural gas-fired generation plant on land owned by Chugach	70.00%
Payments made on contracts associated with power project	15.2
Accepted By Board Of Directors On March 27, 2013 [Member]
Number of collective bargaining agreements ratified and accepted	2
Date of collective bargaining agreement acceptance	Mar. 27, 2013
Accepted By Board Of Directors On April 24, 2013 [Member]
Number of collective bargaining agreements ratified and accepted	1
Date of collective bargaining agreement acceptance	Apr. 24, 2013
ConocoPhillips (COP) [Member]
Expiration date of long term contract for purchase of gas supply	December 31, 2016
Estimated amount of gas under contract	60,000
Marathon Alaska Production, LLC [Member]
Expiration date of long term contract for purchase of gas supply	December 31, 2014
Estimated amount of gas under contract	40,000