Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2016

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,
		2016			2015
	(years)	(in thousands)
Land, land rights and easements	54 – 96	$	138,963		$	135,930
Building and improvements	27 – 64	225,003			219,907
Transmission, distribution, and storage	15 – 85	2,933,788			2,785,944
Generation	25 – 50	1,167,525			1,154,513
Plant acquisition adjustment	25 – 50	685,417			685,417
Other	2 – 45	472,264			445,679
Construction work in process	–—	116,995			75,694
Total property, plant and equipment		5,739,955			5,503,084
Less accumulated depreciation		(1,525,063		)	(1,443,585		)
Net property, plant and equipment		$	4,214,892		$	4,059,499

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, 2016
Ownership percentages	23.4		%	8.7		%	10.0		%	30.0		%
Plant in service	$	153,623		$	60,491		$	50,802		$	297,289
Accumulated depreciation	38,894			29,235			37,099			77,513
December 31, 2015
Ownership percentages	23.4		%	8.7		%	10.0		%	30.0		%
Plant in service	$	153,740		$	60,088		$	46,387		$	289,604
Accumulated depreciation	37,522			27,940			37,160			73,328