Investments (Details-1) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale securities:
Cost basis		$ 2,216	$ 2,225
Gross unrealized gains		346	599
Gross unrealized losses		(8)	(2)
Fair Value		2,554	2,822
Equity method investments:
Equity method investments		73,616	70,650
Other Investments		120	159
Total investments		76,290	73,631
Results of Investment Liquidation [Abstract]
Proceeds from sale of investments		408	19	$ 38
Gain (loss) on sale of investments		121	10	21
ATC and ATC Holdco [Member]
Equity method investments:
Equity method investments	[1]	72,458	69,466
Other Equity Method Investments [Member]
Equity method investments:
Equity method investments		1,158	1,184
MGE [Member]
Available-for-sale securities:
Cost basis		455	480
Gross unrealized gains		40	40
Gross unrealized losses		(8)	(2)
Fair Value		487	518
Equity method investments:
Equity method investments		0	69,466
Other Investments		0	0
Total investments		487	69,984
Results of Investment Liquidation [Abstract]
Proceeds from sale of investments		16	19	0
Gain (loss) on sale of investments		(8)	10	$ 0
MGE [Member] | ATC and ATC Holdco [Member]
Equity method investments:
Equity method investments	[1]	0	69,466
MGE [Member] | Other Equity Method Investments [Member]
Equity method investments:
Equity method investments		$ 0	$ 0

[1] MGE Transco holds an ownership interest in ATC, and MGEE Transco holds an ownership interest in ATC Holdco. In July 2016, MGE's ownership interest in MGE Transco declined below a majority, resulting in MGE Energy's investment in MGE Transco being deconsolidated from MGE's consolidated financial statements. See Footnote 8 for further discussion of noncontrolling interest. In December 2016, MGE's ownership interest in MGE Transco was transferred to MGE Energy, see "ATC and ATC Holdco" below f or additional information.