Jointly owned facilities (Tables)

12 Months Ended

Dec. 31, 2015

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:

	2015		2014
	(In thousands)
Big Stone Station:
Utility plant in service	$	157,761	$	64,283
Less accumulated depreciation	48,242		43,043
	$	109,519	$	21,240
Coyote Station:
Utility plant in service	$	140,895	$	138,810
Less accumulated depreciation	94,755		94,443
	$	46,140	$	44,367
Wygen III:
Utility plant in service	$	65,023	$	65,597
Less accumulated depreciation	6,788		5,928
	$	58,235	$	59,669