Jointly owned facilities (Tables)

12 Months Ended

Dec. 31, 2018

Regulated Operations [Abstract]

Company's share of the cost of utility plant in service and related accumulated depreciation for the stations

At December 31, the Company's share of the cost of utility plant in service and related accumulated depreciation for the stations was as follows:

	2018		2017
	(In thousands)
Big Stone Station:
Utility plant in service	$	156,534	$	158,084
Less accumulated depreciation	49,345		51,740
	$	107,189	$	106,344
Coyote Station:
Utility plant in service	$	155,236	$	155,287
Less accumulated depreciation	105,565		103,897
	$	49,671	$	51,390
Wygen III:
Utility plant in service	$	65,382	$	65,065
Less accumulated depreciation	9,174		7,652
	$	56,208	$	57,413