Jointly owned facilities (Tables)

12 Months Ended

Dec. 31, 2016

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:

	2016		2015
	(In thousands)
Big Stone Station:
Utility plant in service	$	157,144	$	157,761
Less accumulated depreciation	49,568		48,242
	$	107,576	$	109,519
Coyote Station:
Utility plant in service	$	156,334	$	140,895
Less accumulated depreciation	105,928		94,755
	$	50,406	$	46,140
Wygen III:
Utility plant in service	$	66,251	$	65,023
Less accumulated depreciation	7,550		6,788
	$	58,701	$	58,235