Revenues (Tables)

6 Months Ended

Jun. 30, 2018

Disaggregation of Revenue [Line Items]

Disaggregation of Revenue [Table Text Block]

In the following tables, revenue is classified by the type of goods/services rendered and market/customer type. The tables also reconcile revenue to the reportable segments.

	Three Months Ended June 30, 2018
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	58,734	$	10,912	$	10	$	69,656
Commercial and industrial (C&I)	106,367		9,407		25		115,799
Other	1,782		—		236		2,018
Total retail	166,883		20,319		271		187,473
Interchange	38,370		—		—		38,370
Other	1,360		1,069		—		2,429
Total revenue from contracts with customers	206,613		21,388		271		228,272
Alternative revenue and other	2,889		593		—		3,482
Total revenues	$	209,502	$	21,981	$	271	$	231,754

	Three Months Ended June 30, 2017
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	54,754	$	9,015	$	—	$	63,769
C&I	107,899		8,577		27		116,503
Other	1,678		—		230		1,908
Total retail	164,331		17,592		257		182,180
Interchange	42,965		—		—		42,965
Other	523		910		—		1,433
Total revenue from contracts with customers	207,819		18,502		257		226,578
Alternative revenue and other	2,923		525		—		3,448
Total revenues	$	210,742	$	19,027	$	257	$	230,026

	Six Months Ended June 30, 2018
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	126,537	$	41,238	$	26	$	167,801
Commercial and industrial (C&I)	211,184		33,957		50		245,191
Other	3,388		—		473		3,861
Total retail	341,109		75,195		549		416,853
Interchange	76,044		—		—		76,044
Other	2,864		2,076		—		4,940
Total revenue from contracts with customers	420,017		77,271		549		497,837
Alternative revenue and other	5,851		1,210		—		7,061
Total revenues	$	425,868	$	78,481	$	549	$	504,898

	Six Months Ended June 30, 2017
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	120,797	$	35,643	$	20	$	156,460
C&I	210,279		28,835		51		239,165
Other	3,198		—		461		3,659
Total retail	334,274		64,478		532		399,284
Interchange	85,343		—		—		85,343
Other	1,492		1,818		—		3,310
Total revenue from contracts with customers	421,109		66,296		532		487,937
Alternative revenue and other	5,942		1,078		—		7,020
Total revenues	$	427,051	$	67,374	$	532	$	494,957