Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

Major classifications of property, plant and equipment

The following table presents the major classifications of our property, plant and equipment (in thousands):

	Estimated Useful Life	December 31,
		2019			2018
	(years)	(in thousands)
Land, land rights and easements	50 – 96	$	156,069		$	149,636
Building and improvements	23 – 73	278,164			264,205
Transmission, distribution, and storage	15 – 85	3,569,141			3,341,001
Generation	23 – 71	1,222,796			1,193,117
Plant acquisition adjustment (1)	25 – 50	686,328			686,328
Other	2 – 45	545,009			541,741
Construction work in process	–—	96,421			110,076
Total property, plant and equipment		6,553,928			6,286,104
Less accumulated depreciation		(1,853,004		)	(1,764,786		)
Net property, plant and equipment		$	4,700,924		$	4,521,318

Schedule of jointly owned utility plants

Information relating to our ownership interest in these facilities is as follows (in thousands):

	Big Stone (SD)			Neal #4 (IA)			Coyote (ND)			Colstrip Unit 4 (MT)
December 31, 2019
Ownership percentages	23.4		%	8.7		%	10.0		%	30.0		%
Plant in service	$	155,662		$	62,565		$	52,448		$	311,399
Accumulated depreciation	40,988			32,853			38,310			97,563
December 31, 2018
Ownership percentages	23.4		%	8.7		%	10.0		%	30.0		%
Plant in service	$	155,359		$	60,758		$	50,325		$	309,163
Accumulated depreciation	42,235			31,542			37,955			88,985