Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2020

Property, plant and equipment at December 31 consisted of the following (dollars in thousands):


	2020			2019			Lives (in years)
Electric Utilities	Property, Plant and Equipment		Weighted Average Useful Life (in years)	Property, Plant and Equipment		Weighted Average Useful Life (in years)	Minimum	Maximum

Electric plant:
Production	$	1,417,951	40	$	1,348,049	41	32	46
Electric transmission	517,794		49	483,640		51	44	51
Electric distribution	959,453		46	861,042		47	46	48
Plant acquisition adjustment (a)	4,870		32	4,870		32	32	32
General	259,010		28	259,266		28	26	29
Total electric plant in service	3,159,078			2,956,867
Construction work in progress	89,402			102,268
Total electric plant	3,248,480			3,059,135
Less accumulated depreciation	(666,669)			(670,861)
Electric plant net of accumulated depreciation	$	2,581,811		$	2,388,274

_____________

(a) The plant acquisition adjustment is included in rate base and is being recovered with 10 years remaining.


	2020			2019			Lives (in years)
Gas Utilities	Property, Plant and Equipment		Weighted Average Useful Life (in years)	Property, Plant and Equipment		Weighted Average Useful Life (in years)	Minimum	Maximum

Gas plant:
Production	$	15,603	40	$	13,000	35	24	46
Gas transmission	578,278		54	516,172		50	22	71
Gas distribution	2,115,082		53	1,857,233		43	45	59
Cushion gas - depreciable (a)	3,539		28	3,539		28	28	28
Cushion gas - not depreciable (a)	39,184		N/A	44,443		N/A	N/A	N/A
Storage	55,481		38	46,977		31	24	52
General	438,217		19	437,054		20	12	23
Total gas plant in service	3,245,384			2,918,418
Construction work in progress	67,229			63,080
Total gas plant	3,312,613			2,981,498
Less accumulated depreciation	(323,679)			(336,721)
Gas plant net of accumulated depreciation	$	2,988,934		$	2,644,777

_____________

(a) Depreciation of Cushion Gas is determined by the respective regulatory jurisdiction in which the Cushion Gas resides.


2020											Lives (in years)
	Property, Plant and Equipment		Construction Work in Progress		Total Property Plant and Equipment		Less Accumulated Depreciation and Depletion		Net Property, Plant and Equipment		Weighted Average Useful Life	Minimum	Maximum

Power Generation	$	529,927	$	4,876	$	534,803	$	(167,787)	$	367,016	31	2	40
Mining	$	186,552	$	988	$	187,540	$	(126,537)	$	61,003	14	2	59


2019											Lives (in years)
	Property, Plant and Equipment		Construction Work in Progress		Total Property Plant and Equipment		Less Accumulated Depreciation and Depletion		Net Property, Plant and Equipment		Weighted Average Useful Life	Minimum	Maximum

Power Generation	$	532,397	$	2,121	$	534,518	$	(154,362)	$	380,156	31	2	40
Mining	$	179,198	$	1,275	$	180,473	$	(118,585)	$	61,888	13	2	59


2020											Lives (in years)
	Property, Plant and Equipment		Construction Work in Progress		Total Property Plant and Equipment		Less Accumulated Depreciation		Net Property, Plant and Equipment		Weighted Average Useful Life	Minimum	Maximum
Corporate	$	5,692	$	16,402	$	22,094	$	(1,144)	$	20,950	10	10	22


2019											Lives (in years)
	Property, Plant and Equipment		Construction Work in Progress		Total Property Plant and Equipment		Less Accumulated Depreciation		Net Property, Plant and Equipment		Weighted Average Useful Life	Minimum	Maximum
Corporate	$	5,721	$	23,334	$	29,055	$	(964)	$	28,091	10	3	30