Eklutna Hydroelectric Project (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Jointly Owned Utility Plant Interests [Line Items]
Percentage ownership	70.00%								70.00%
Net utility plant	$ 661,346,913				$ 598,085,816				$ 661,346,913	$ 598,085,816
Net utility plant	661,346,913				598,085,816				661,346,913	598,085,816
Less accumulated depreciation	(493,894,390)				(470,282,210)				(493,894,390)	(470,282,210)
Accumulated depreciation	493,894,390				470,282,210				493,894,390	470,282,210
Total operating expenses	68,250,215	60,200,529	55,725,151	64,019,060	70,143,069	65,509,750	65,592,311	61,096,736	248,194,955	262,341,866	233,967,201
Eklutna Hydroelectric Project [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percentage ownership	30.00%								30.00%
Net utility plant	4,725,470				4,880,583				4,725,470	4,880,583
Net utility plant	4,725,470				4,880,583				4,725,470	4,880,583
Less accumulated depreciation	(1,671,335)				(1,491,704)				(1,671,335)	(1,491,704)
Accumulated depreciation	1,671,335				1,491,704				1,671,335	1,491,704
Total operating expenses									$ 682,757	$ 662,035	$ 664,747
Matanuska Electric Association, Inc. [Member] | Eklutna Hydroelectric Project [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percentage ownership	16.70%								16.70%
Municipal Light & Power [Member] | Eklutna Hydroelectric Project [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percentage ownership	53.30%								53.30%