Revenues (Tables)

3 Months Ended

Mar. 31, 2018

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue [Table Text Block]

	Three Months Ended
(Thousands of Dollars)	March 31, 2018		March 31, 2017
Major product lines
Revenue from contracts with customers:
Residential	$	80,049	$	79,601
Commercial and industrial (C&I)	195,771		200,957
Other	9,664		9,612
Total retail	285,484		290,170
Wholesale	93,232		91,141
Transmission	55,646		54,178
Other	7,531		1,945
Total revenue from contracts with customers	441,893		437,434
Alternative revenue and other	5,339		22,638
Total revenues	$	447,232	$	460,072