Eklutna Hydroelectric Project (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Jointly Owned Utility Plant Interests [Line Items]
Net utility plant	$ 714,871,678				$ 674,876,440				$ 714,871,678	$ 674,876,440
Accumulated depreciation	496,098,131				469,199,226				496,098,131	469,199,226
Total operating expenses	$ 47,000,307	$ 40,308,301	$ 41,472,710	$ 42,359,071	42,182,178	$ 39,667,546	$ 43,490,558	$ 63,451,276	$ 171,140,389	188,791,558	$ 252,972,879
Eklutna Hydroelectric Project [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percentage ownership	30.00%								30.00%
Net utility plant	$ 4,229,167				4,401,440				$ 4,229,167	4,401,440
Accumulated depreciation	$ 2,442,175				$ 2,203,659				2,442,175	2,203,659
Total operating expenses									$ 532,678	$ 689,501	$ 761,613
Matanuska Electric Association, Inc. [Member] | Eklutna Hydroelectric Project [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percentage ownership	17.00%								17.00%
Municipal Light & Power [Member] | Eklutna Hydroelectric Project [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percentage ownership	53.00%								53.00%