Variable Interest Entities (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2016 USD ($) MW	Dec. 31, 2015 USD ($) MW
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Property, plant, and equipment, net		$ 1,245,269	$ 1,217,094
Construction work in progress		36,790	26,351
Accrued interest and taxes		5,495	5,067
Deferred income taxes		383,813	$ 360,785
Long-term debt, gross, current and noncurrent		$ 391,242
Other Variable Interest Entities
Other variable interest entities, purchase power agreement, plant capacity (in MW) | MW		51	61
MGE Power Elm Road [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Property, plant, and equipment, net		$ 175,502	$ 177,904
Construction work in progress		3,241	2,400
Deferred income taxes		42,525	40,865
Long-term debt		62,021	64,622
Noncontrolling interest	[1]	80,362	79,113
Long-term debt, gross, current and noncurrent		62,600
Total carrying costs		62,500
Total capitalized interest		17,000
Total capitalized cost of equity		$ 45,500
Carrying cost rate recovery period		6 years
MGE Power Elm Road [Member] | Minimum [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Debt service coverage ratio		1.25
MGE Power West Campus [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Property, plant, and equipment, net		$ 81,588	84,403
Affiliate receivables, current and noncurrent		4,769	5,295
Deferred income taxes		19,912	19,612
Long-term debt		44,932	46,510
Noncontrolling interest	[1]	35,303	$ 37,603
Long-term debt, gross, current and noncurrent		45,100
Carrying costs recovered		$ 12,100
Carrying cost rate recovery period		10 years
MGE Power West Campus [Member] | Minimum [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Debt service coverage ratio		1.25
MGE Power West Campus [Member] | Maximum [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Debt to total capitalization ratio		0.65

[1] MGE Power Elm Road and MGE Power West Campus are not su bsidiaries of MGE; however, they have been consolidated in the consolidated financial statements of MGE (see Footnote 2). MGE Power Elm Road and MGE Power West Campus are 100 % owned by MGE Power, and MGE Power is 100 % o wned by MGE Energy. MGE Energy's proportionate share of the equity and net income (through its wholly owned subsidiary MGE Power) of MGE Power Elm Road and MGE Power West Campus is classified within the MGE consolidated financial statements as noncontrolling interest.