Business Segment Information:

9 Months Ended

Sep. 30, 2020

Segment Reporting Information, Additional Information [Abstract]

Business Segment Information

Business Segment Information

Our reportable segments are based on our method of internal reporting, which is generally segregated by differences in products, services and regulation. All of our operations and assets are located within the United States.

Segment and Corporate and Other information is as follows (in thousands):

Three Months Ended September 30, 2020	External Operating Revenue				Inter-company Operating Revenue				Total Revenues
	Contract Customers		Other Revenues		Contract Customers		Other Revenues
Segment:
Electric Utilities	$	194,941	$	224	$	5,677	$	—	$	200,842
Gas Utilities	141,275		863		1,601		190		143,929
Power Generation	1,528		414		24,521		55		26,518
Mining	6,568		777		8,100		(209)		15,236
Inter-company eliminations	—		—		(39,899)		(36)		(39,935)
Total	$	344,312	$	2,278	$	—	$	—	$	346,590

Three Months Ended September 30, 2019	External Operating Revenue				Inter-company Operating Revenue				Total Revenues
	Contract Customers		Other Revenues		Contract Customers		Other Revenues
Segment:
Electric Utilities	$	185,811	$	234	$	5,339	$	—	$	191,384
Gas Utilities	129,385		810		549		—		130,744
Power Generation	1,703		531		14,415		9,162		25,811
Mining	6,846		228		8,146		332		15,552
Inter-company eliminations	—		—		(28,449)		(9,494)		(37,943)
Total	$	323,745	$	1,803	$	—	$	—	$	325,548

Nine Months Ended September 30, 2020	External Operating Revenue				Inter-company Operating Revenue				Total Revenues
	Contract Customers		Other Revenues		Contract Customers		Other Revenues
Segment:
Electric Utilities	$	518,641	$	2,074	$	17,466	$	—	$	538,181
Gas Utilities	655,386		7,083		3,153		190		665,812
Power Generation	4,625		1,206		72,609		166		78,606
Mining	20,062		1,477		23,855		463		45,857
Inter-company eliminations	—		—		(117,083)		(819)		(117,902)
Total	$	1,198,714	$	11,840	$	—	$	—	$	1,210,554

Nine Months Ended September 30, 2019	External Operating Revenue				Inter-company Operating Revenue				Total Revenues
	Contract Customers		Other Revenues		Contract Customers		Other Revenues
Segment:
Electric Utilities	$	521,614	$	2,465	$	16,586	$	—	$	540,665
Gas Utilities	704,188		1,134		1,971		—		707,293
Power Generation	5,725		1,401		40,924		27,714		75,764
Mining	19,934		785		23,315		992		45,026
Inter-company eliminations	—		—		(82,796)		(28,706)		(111,502)
Total	$	1,251,461	$	5,785	$	—	$	—	$	1,257,246

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Adjusted operating income (a):
Electric Utilities	$	52,083	$	50,653	$	121,726	$	125,219
Gas Utilities	18,147		4,736		139,253		116,607
Power Generation	8,738		11,822		31,489		33,945
Mining	3,505		3,374		9,992		9,351
Corporate and Other	(239)		(34)		(108)		(439)
Operating income	82,234		70,551		302,352		284,683
Interest expense, net	(36,041)		(33,487)		(107,039)		(102,469)
Impairment of investment	—		(19,741)		(6,859)		(19,741)
Other income (expense), net	(1,193)		580		(703)		55
Income tax (expense)	(4,651)		(2,508)		(25,484)		(22,078)
Net income	40,349		15,395		162,267		140,450
Net income attributable to noncontrolling interest	(4,066)		(3,655)		(11,844)		(10,319)
Net income available for common stock	$	36,283	$	11,740	$	150,423	$	130,131

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(a)    Adjusted operating income recognizes inter-segment revenues and costs for Colorado Electric’s PPA with Black Hills Colorado IPP on an accrual basis rather than as a finance lease. This presentation of segment information does not impact consolidated financial results.

Segment and Corporate and Other balances included in the accompanying Condensed Consolidated Balance Sheets were as follows (in thousands):

Total assets (net of inter-company eliminations) as of:	September 30, 2020		December 31, 2019
Segment:
Electric Utilities	$	3,040,064	$	2,900,983
Gas Utilities	4,201,325		4,032,339
Power Generation	403,491		417,715
Mining	75,752		77,175
Corporate and Other	108,418		130,245
Total assets	$	7,829,050	$	7,558,457