Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2021

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,
		2021		2020
	(years)	(in thousands)
Transmission, distribution, and storage	15 – 95	$	4,004,819	$	3,771,023
Generation	23 – 72	1,287,517		1,252,805
Plant acquisition adjustment(1)	25 – 50	686,328		686,328
Building and improvements	23 – 73	296,955		303,099
Land, land rights and easements	53 – 96	161,585		157,379
Other	2 – 45	585,448		571,981
Construction work in process	–—	294,617		173,492
Total property, plant and equipment		7,317,269		6,916,107
Less accumulated depreciation		(1,787,550)		(1,703,016)
Less accumulated amortization		(282,487)		(260,156)
Net property, plant and equipment		$	5,247,232	$	4,952,935

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, 2021
Ownership percentages	23.4		%	8.7		%	10.0		%	30.0		%
Plant in service	$	154,375		$	62,865		$	51,652		$	324,433
Accumulated depreciation	42,102			34,629			38,453			113,805
December 31, 2020
Ownership percentages	23.4		%	8.7		%	10.0		%	30.0		%
Plant in service	$	153,632		$	62,927		$	51,586		$	317,438
Accumulated depreciation	40,665			33,942			37,980			105,738