Black Hills (BKH) 10-Q 3 Nov 21 2021 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2021	Oct. 31, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-31303
Entity Registrant Name	Black Hills Corporation
Entity Incorporation, State or Country Code	SD
Entity Tax Identification Number	46-0458824
Entity Address, Address Line One	7001 Mount Rushmore Road
Entity Address, City or Town	Rapid City
Entity Address, State or Province	SD
Entity Address, Postal Zip Code	57702
City Area Code	605
Local Phone Number	721-1700
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Title of 12(b) Security	Common stock of $1.00 par value
Trading Symbol	BKH
Security Exchange Name	NYSE
Entity Common Stock, Shares Outstanding		63,820,271
Entity Central Index Key	0001130464
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Revenues	$ 380,590	$ 346,590	$ 1,386,594	$ 1,210,554
Operating expenses:
Fuel, purchased power and cost of natural gas sold	94,057	71,686	495,678	331,194
Operations and maintenance	122,277	122,759	375,201	365,533
Depreciation, depletion and amortization	59,159	56,348	174,871	169,413
Taxes - property and production	15,224	13,563	45,390	42,062
Total operating expenses	290,717	264,356	1,091,140	908,202
Operating income	89,873	82,234	295,454	302,352
Other income (expense):
Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts)	(38,604)	(36,521)	(115,098)	(108,067)
Interest income	586	480	1,278	1,028
Impairment of investment	0	0	0	(6,859)
Other income (expense), net	1,560	(1,193)	1,635	(703)
Total other income (expense)	(36,458)	(37,234)	(112,185)	(114,601)
Income before income taxes	53,415	45,000	183,269	187,751
Income tax (expense)	(5,253)	(4,651)	(6,333)	(25,484)
Net income	48,162	40,349	176,936	162,267
Net income attributable to non-controlling interest	(4,050)	(4,066)	(11,347)	(11,844)
Net income available for common stock	$ 44,112	$ 36,283	$ 165,589	$ 150,423
Earnings per share of common stock:
Earnings per share, Basic (usd per share)	$ 0.70	$ 0.58	$ 2.63	$ 2.41
Earnings per share, Diluted (usd per share)	$ 0.70	$ 0.58	$ 2.63	$ 2.41
Weighted average common shares outstanding:
Basic (in shares)	63,341	62,575	62,950	62,310
Diluted (in shares)	63,436	62,630	63,046	62,362

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net income	$ 48,162	$ 40,349	$ 176,936	$ 162,267
Other comprehensive income (loss), net of tax:
Benefit plan liability adjustments - net gain (net of tax of $0, $0, $0 and $(17), respectively)	0	0	0	55
Reclassification adjustments of benefit plan liability - prior service cost (net of tax of $6, $6, $21 and $19, respectively)	(19)	(18)	(53)	(60)
Reclassification adjustments of benefit plan liability - net loss (net of tax of $(139), $(149), $(513) and $(426), respectively)	459	448	1,280	1,365
Other comprehensive income, net of tax	5,277	1,512	8,177	3,733
Comprehensive income	53,439	41,861	185,113	166,000
Net income attributable to non-controlling interest	(4,050)	(4,066)	(11,347)	(11,844)
Comprehensive income available for common stock	49,389	37,795	173,766	154,156
Interest rate swaps
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses on settled/amortized derivatives, net of tax	657	544	1,743	1,630
Commodity Contract
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses on settled/amortized derivatives, net of tax	(250)	137	(269)	562
Net unrealized gains (losses) on commodity derivatives (net of tax of $(1,437), $(112), $(1,776) and $(44), respectively)	$ 4,430	$ 401	$ 5,476	$ 181

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
(Tax) benefit on benefit plan liability adjustments - net gain (loss)	$ 0	$ 0	$ 0	$ (17)
(Tax) benefit on benefit plan liability adjustments - prior service costs	6	6	21	19
(Tax) benefit on reclassification adjustment of benefit plan liability - net loss	(139)	(149)	(513)	(426)
Interest rate swaps
(Tax) benefit on reclassification of net realized (gains) losses on settled/amortized derivatives	(55)	(168)	(395)	(508)
Commodity Contract
(Tax) benefit on reclassification of net realized (gains) losses on settled/amortized derivatives	81	(41)	87	(172)
(Tax) benefit on net unrealized gains (losses) on commodity derivatives	$ (1,437)	$ (112)	$ (1,776)	$ (44)

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 10,181	$ 6,356
Restricted cash and equivalents	4,753	4,383
Accounts receivable, net	181,956	265,961
Materials, supplies and fuel	145,743	117,400
Derivative assets, current	12,316	1,848
Income tax receivable, net	17,472	19,446
Regulatory assets, current	213,031	51,676
Other current assets	42,274	26,221
Total current assets	627,726	493,291
Property, plant and equipment	7,697,880	7,305,530
Less: accumulated depreciation and depletion	(1,380,304)	(1,285,816)
Total property, plant and equipment, net	6,317,576	6,019,714
Other assets:
Goodwill	1,299,454	1,299,454
Intangible assets, net	11,063	11,944
Regulatory assets, non-current	617,024	226,582
Other assets, non-current	37,547	37,801
Total other assets, non-current	1,965,088	1,575,781
TOTAL ASSETS	8,910,390	8,088,786
Current liabilities:
Accounts payable	142,130	183,340
Accrued liabilities	249,835	243,612
Derivative liabilities, current	3,471	2,044
Regulatory liabilities, current	30,156	25,061
Notes payable	332,525	234,040
Current maturities of long-term debt	0	8,436
Total current liabilities	758,117	696,533
Long-term debt, net of current maturities	4,125,571	3,528,100
Deferred credits and other liabilities:
Deferred income tax liabilities, net	445,036	408,624
Regulatory liabilities, non-current	496,261	507,659
Benefit plan liabilities	150,727	150,556
Other deferred credits and other liabilities	134,776	134,667
Total deferred credits and other liabilities	1,226,800	1,201,506
Commitments, contingencies and guarantees (Note 3)
Equity:
Common stock $1 par value; 100,000,000 shares authorized; issued 63,865,151 and 62,827,179 shares, respectively	63,865	62,827
Additional paid-in capital	1,726,277	1,657,285
Retained earnings	929,369	870,738
Treasury stock, at cost – 43,885 and 32,492 shares, respectively	(2,819)	(2,119)
Accumulated other comprehensive income (loss)	(19,169)	(27,346)
Total stockholders’ equity	2,697,523	2,561,385
Non-controlling interest	102,379	101,262
Total equity	2,799,902	2,662,647
TOTAL LIABILITIES AND TOTAL EQUITY	$ 8,910,390	$ 8,088,786

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Common stock, par value (usd per share)	$ 1	$ 1
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares, issued	63,865,151	62,827,179
Treasury stock, shares	43,885	32,492

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating activities:
Net income	$ 176,936	$ 162,267
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation, depletion and amortization	174,871	169,413
Deferred financing cost amortization	3,892	5,523
Impairment of investment	0	6,859
Stock compensation	7,245	2,696
Deferred income taxes	5,844	28,502
Employee benefit plans	6,779	9,294
Other adjustments, net	2,708	7,910
Changes in certain operating assets and liabilities:
Materials, supplies and fuel	(29,948)	(10,905)
Accounts receivable and other current assets	97,348	75,960
Accounts payable and other current liabilities	(20,094)	(11,136)
Regulatory assets	(559,389)	1,954
Regulatory liabilities	(9,533)	(17,686)
Contributions to defined benefit pension plans	0	(12,700)
Other operating activities, net	(1,419)	1,508
Net cash provided by (used in) operating activities	(144,760)	419,459
Investing activities:
Property, plant and equipment additions	(497,849)	(535,993)
Other investing activities	13,743	6,269
Net cash (used in) investing activities	(484,106)	(529,724)
Financing activities:
Dividends paid on common stock	(106,957)	(99,999)
Common stock issued	62,977	99,316
Term loan - borrowings	800,000	0
Term loan - repayments	(800,000)	0
Net borrowings (payments) of Revolving Credit Facility and CP Program	98,485	(265,180)
Long-term debt - issuances	600,000	400,000
Long-term debt - repayments	(8,436)	(7,163)
Distributions to non-controlling interest	(10,230)	(12,636)
Other financing activities	(2,778)	(6,519)
Net cash provided by financing activities	633,061	107,819
Net change in cash, restricted cash and cash equivalents	4,195	(2,446)
Cash, restricted cash and cash equivalents at beginning of period	10,739	13,658
Cash, restricted cash and cash equivalents at end of period	14,934	11,212
Supplemental cash flow information:
Interest, net of amounts capitalized	(93,325)	(87,453)
Income taxes	1,486	1,256
Accrued property, plant and equipment purchases at September 30	$ 55,619	$ 86,474

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Equity (unaudited) - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Retained EarningsCumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (loss)	Noncontrolling Interest
Beginning balance (in shares) at Dec. 31, 2019			61,480,658	3,956
Beginning balance at Dec. 31, 2019	$ 2,464,069		$ 61,481	$ (267)	$ 1,552,788	$ 778,776		$ (30,655)	$ 101,946
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	97,224					93,174			4,050
Other comprehensive income, net of tax	1,273							1,273
Dividends on common stock	(32,902)					(32,902)
Share-based compensation (in shares)			69,378	20,700
Share-based compensation	674		$ 69	$ (1,658)	2,263
Issuance of common stock (in shares)			1,222,942
Issuance of common stock	100,000		$ 1,223		98,777
Issuance costs	(967)				(967)
Distributions to non-controlling interest	(4,741)								(4,741)
Ending balance (in shares) at Mar. 31, 2020			62,772,978	24,656
Ending balance at Mar. 31, 2020	2,624,423	$ (207)	$ 62,773	$ (1,925)	1,652,861	838,841	$ (207)	(29,382)	101,255
Beginning balance (in shares) at Dec. 31, 2019			61,480,658	3,956
Beginning balance at Dec. 31, 2019	2,464,069		$ 61,481	$ (267)	1,552,788	778,776		(30,655)	101,946
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	162,267
Other comprehensive income, net of tax	3,733
Ending balance (in shares) at Sep. 30, 2020			62,773,015	24,897
Ending balance at Sep. 30, 2020	2,620,200		$ 62,773	$ (1,710)	1,655,912	828,993		(26,922)	101,154
Beginning balance (in shares) at Mar. 31, 2020			62,772,978	24,656
Beginning balance at Mar. 31, 2020	2,624,423	$ (207)	$ 62,773	$ (1,925)	1,652,861	838,841	$ (207)	(29,382)	101,255
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	24,694					20,966			3,728
Other comprehensive income, net of tax	948							948
Dividends on common stock	(33,538)					(33,538)
Share-based compensation (in shares)			18	1,743
Share-based compensation	1,827		$ 0	$ 46	1,781
Issuance costs	(79)				(79)
Distributions to non-controlling interest	(3,779)								(3,779)
Ending balance (in shares) at Jun. 30, 2020			62,772,996	26,399
Ending balance at Jun. 30, 2020	2,614,496		$ 62,773	$ (1,879)	1,654,563	826,269		(28,434)	101,204
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,349					36,283			4,066
Other comprehensive income, net of tax	1,512							1,512
Dividends on common stock	(33,559)					(33,559)
Share-based compensation (in shares)			19	(1,502)
Share-based compensation	1,637		$ 0	$ 169	1,468
Issuance costs	(119)				(119)
Distributions to non-controlling interest	(4,116)								(4,116)
Ending balance (in shares) at Sep. 30, 2020			62,773,015	24,897
Ending balance at Sep. 30, 2020	2,620,200		$ 62,773	$ (1,710)	1,655,912	828,993		(26,922)	101,154
Beginning balance (in shares) at Dec. 31, 2020			62,827,179	32,492
Beginning balance at Dec. 31, 2020	2,662,647		$ 62,827	$ (2,119)	1,657,285	870,738		(27,346)	101,262
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	100,487					96,316			4,171
Other comprehensive income, net of tax	1,018							1,018
Dividends on common stock	(35,514)					(35,514)
Share-based compensation (in shares)			82,794	7,448
Share-based compensation	1,310		$ 83	$ (445)	1,672
Other	(2)					(2)
Distributions to non-controlling interest	(4,644)								(4,644)
Ending balance (in shares) at Mar. 31, 2021			62,909,973	39,940
Ending balance at Mar. 31, 2021	2,725,302		$ 62,910	$ (2,564)	1,658,957	931,538		(26,328)	100,789
Beginning balance (in shares) at Dec. 31, 2020			62,827,179	32,492
Beginning balance at Dec. 31, 2020	2,662,647		$ 62,827	$ (2,119)	1,657,285	870,738		(27,346)	101,262
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	176,936
Other comprehensive income, net of tax	8,177
Ending balance (in shares) at Sep. 30, 2021			63,865,151	43,885
Ending balance at Sep. 30, 2021	2,799,902		$ 63,865	$ (2,819)	1,726,277	929,369		(19,169)	102,379
Beginning balance (in shares) at Mar. 31, 2021			62,909,973	39,940
Beginning balance at Mar. 31, 2021	2,725,302		$ 62,910	$ (2,564)	1,658,957	931,538		(26,328)	100,789
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	28,287					25,161			3,126
Other comprehensive income, net of tax	1,882							1,882
Dividends on common stock	(35,578)					(35,578)
Share-based compensation (in shares)			20,905	6,588
Share-based compensation	3,295		$ 21	$ (424)	3,698
Issuance of common stock (in shares)			596,035
Issuance of common stock	40,232		$ 596		39,636
Issuance costs	(466)				(466)
Other	1					1
Distributions to non-controlling interest	(4,061)								(4,061)
Ending balance (in shares) at Jun. 30, 2021			63,526,913	46,528
Ending balance at Jun. 30, 2021	2,758,894		$ 63,527	$ (2,988)	1,701,825	921,122		(24,446)	99,854
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	48,162					44,112			4,050
Other comprehensive income, net of tax	5,277							5,277
Dividends on common stock	(35,865)					(35,865)
Share-based compensation (in shares)			17	(2,643)
Share-based compensation	2,018		$ 0	$ 169	1,849
Issuance of common stock (in shares)			338,221
Issuance of common stock	23,172		$ 338		22,834
Issuance costs	(231)				(231)
Distributions to non-controlling interest	(1,525)								(1,525)
Ending balance (in shares) at Sep. 30, 2021			63,865,151	43,885
Ending balance at Sep. 30, 2021	$ 2,799,902		$ 63,865	$ (2,819)	$ 1,726,277	$ 929,369		$ (19,169)	$ 102,379

Condensed Consolidated Statem_6

Condensed Consolidated Statements of Equity (unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Dividends on common stock (usd per share)	$ 0.565	$ 0.565	$ 0.565	$ 0.535	$ 0.535	$ 0.535

Management's Statements_

Management's Statements:	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Management's Statement	Management’s Statement The unaudited Condensed Consolidated Financial Statements included herein have been prepared by Black Hills Corporation (together with our subsidiaries the “Company”, “us”, “we” or “our”), pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America have been condensed or omitted pursuant to such rules and regulations; however, we believe that the footnotes adequately disclose the information presented. These Condensed Consolidated Financial Statements should be read in conjunction with the consolidated financial statements and the notes included in our 2020 Annual Report on Form 10-K. Segment Reporting We conduct our operations through the following reportable segments: Electric Utilities, Gas Utilities, Power Generation and Mining. 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. Use of Estimates and Basis of Presentation The information furnished in the accompanying Condensed Consolidated Financial Statements reflects certain estimates required and all adjustments, including accruals, which are, in the opinion of management, necessary for a fair presentation of the September 30, 2021, December 31, 2020 and September 30, 2020 financial information. Certain lines of business in which we operate are highly seasonal, and our interim results of operations are not necessarily indicative of the results of operations to be expected for an entire year. COVID-19 Pandemic In March 2020, the World Health Organization categorized COVID-19 as a pandemic and the President of the United States declared the outbreak a national emergency. The U.S. government has deemed the electric and natural gas utilities to be critical infrastructure sectors that provide essential services during this emergency. As a provider of essential services, the Company has an obligation to provide services to our customers. The Company remains focused on protecting the health of our customers, employees and the communities in which we operate while assuring the continuity of our business operations. The Company’s Condensed Consolidated Financial Statements reflect estimates and assumptions made by management that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the Condensed Consolidated Financial Statements and reported amounts of revenue and expenses during the reporting periods presented. The Company considered the impacts of COVID-19 on the assumptions and estimates used and determined that for the three and nine months ended September 30, 2021, there were no material adverse impacts on the Company’s results of operations. Recently Issued Accounting Standards Facilitation of the Effects of Reference Rate Reform on Financial Reporting, ASU 2020-04 In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which was subsequently amended by ASU 2021-01. The standard provides relief for companies preparing for discontinuation of interest rates, such as LIBOR, and allows optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions affected by reference rate reform if certain criteria are met. The amendments in this update are elective and are effective upon the ASU issuance through December 31, 2022. We are currently evaluating whether we will apply the optional guidance as we assess the impact of the discontinuance of LIBOR on our current arrangements and the potential impact on our financial position, results of operations and cash flows. Recently Adopted Accounting Standards Simplifying the Accounting for Income Taxes, ASU 2019-12 In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes as part of its overall simplification initiative to reduce costs and complexity in applying accounting standards while maintaining or improving the usefulness of the information provided to users of the financial statements. Amendments include removal of certain exceptions to the general principles of ASC 740, Income Taxes , and simplification in several other areas such as accounting for a franchise tax (or similar tax) that is partially based on income. We adopted this standard prospectively on January 1, 2021. Adoption of this standard did not have an impact on our financial position, results of operations or cash flows.

Regulatory Matters_

Regulatory Matters:	9 Months Ended
	Sep. 30, 2021
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Matters	Regulatory Matters We had the following regulatory assets and liabilities (in thousands): As of As of September 30, 2021 December 31, 2020 Regulatory assets Winter Storm Uri (a) $ 532,766 $ — Deferred energy and fuel cost adjustments (b) 59,741 39,035 Deferred gas cost adjustments (b) 6,076 3,200 Gas price derivatives (b) — 2,226 Deferred taxes on AFUDC (c) 7,537 7,491 Employee benefit plans and related deferred taxes (d) 114,234 116,598 Environmental (b) 1,395 1,413 Loss on reacquired debt (b) 21,460 22,864 Deferred taxes on flow through accounting (d) 54,199 47,515 Decommissioning costs (b) 6,583 8,988 Gas supply contract termination (b) — 2,524 Other regulatory assets (b) 26,064 26,404 Total regulatory assets 830,055 278,258 Less current regulatory assets (213,031) (51,676) Regulatory assets, non-current $ 617,024 $ 226,582 Regulatory liabilities Deferred energy and gas costs (b) $ 9,408 $ 13,253 Gas price derivatives (b) 13,234 — Employee benefit plan costs and related deferred taxes (d) 39,203 40,256 Cost of removal (b) 181,180 172,902 Excess deferred income taxes (d) 266,477 285,259 Other regulatory liabilities (d) 16,915 21,050 Total regulatory liabilities 526,417 532,720 Less current regulatory liabilities (30,156) (25,061) Regulatory liabilities, non-current $ 496,261 $ 507,659 __________ (a) Timing of Winter Storm Uri incremental cost recovery and associated carrying costs are subject to pending applications with our utility commissions. See further information below. (b) Recovery of costs, but we are not allowed a rate of return. (c) In addition to recovery of costs, we are allowed a rate of return. (d) In addition to recovery or repayment of costs, we are allowed a return on a portion of this amount or a reduction in rate base. Regulatory Activity Except as discussed below, there have been no other significant changes to our Regulatory Matters from those previously disclosed in Note 2 of the Notes to the Consolidated Financial Statements in our 2020 Annual Report on Form 10-K. Winter Storm Uri In February 2021, a prolonged period of historic cold temperatures across the central United States, which covered all of our Utilities’ service territories, caused a substantial increase in heating and energy demand and contributed to unforeseeable and unprecedented market prices for natural gas and electricity. As a result of Winter Storm Uri, we incurred significant incremental fuel, purchased power and natural gas costs. Our Utilities submitted Winter Storm Uri cost recovery applications in our state jurisdictions seeking to recover $546 million of these incremental costs through separate tracking mechanisms over a weighted-average recovery period of 3.7 years. These incremental cost estimates are subject to adjustments as final decisions are issued by the respective utility commissions. In these applications, we seek approval to recover carrying costs. For the nine months ended September 30, 2021, $1.8 million of carrying costs were accrued and recorded to a regulatory asset. We are also seeking recovery of $13 million of previously disclosed Winter Storm Uri incremental costs through our existing regulatory mechanisms. To date, Nebraska Gas and South Dakota Electric received commission approval of their Winter Storm Uri cost recovery applications. Additionally, Arkansas Gas, Iowa Gas and Wyoming Gas received approval for interim cost recovery subject to a final decision on carrying costs and recovery periods at a later date. In October 2021, Wyoming Gas filed a settlement agreement for their application with final rates to be implemented January 1, 2022. The settlement is subject to final approval by the commission. For the nine months ended September 30, 2021, our Utilities collected $15 million of Winter Storm Uri incremental costs and carrying costs from customers. TCJA On December 30, 2020, an administrative law judge approved a settlement of Colorado Electric’s plan to provide $9.3 million of TCJA-related bill credits to its customers. The bill credits, which represent a disposition of excess deferred income tax benefits resulting from the TCJA, were delivered to customers in February 2021. The settlement agreement further provided for Colorado Electric to deliver annual bill credits to customers, starting in April 2021, until remaining excess deferred income tax regulatory liabilities associated with the TCJA are fully amortized. In April 2021, Colorado Electric delivered $0.9 million of TCJA-related bill credits to customers. On January 26, 2021, the NPSC approved Nebraska Gas’s plan to provide $2.9 million of TCJA-related bill credits to its customers. The bill credits, which represent a disposition of excess deferred income tax benefits resulting from the TCJA, were delivered to customers in June 2021. These Colorado Electric and Nebraska Gas bill credits, which resulted in a reduction in revenue, were offset by a reduction in income tax expense and resulted in a minimal impact to Net income for the three and nine months ended September 30, 2021. As part of the settlement agreement discussed further below, Kansas Gas will deliver $3.0 million of TCJA and state tax reform benefits to customers, annually, for each of the next three years starting in 2022 (approximately $9.1 million of total benefits expected to be delivered). Colorado Gas Rate Review On June 1, 2021, Colorado Gas filed a rate review with the CPUC seeking recovery of significant infrastructure investments in its 7,000-mile natural gas pipeline system. On October 5, 2021, Colorado Gas reached a settlement agreement with the CPUC Staff and various intervenors for a general rate increase. The settlement agreement is subject to review and approval by an ALJ and the CPUC. If approved, the settlement is expected to generate $6.5 million of new annual revenue with new rates effective January 1, 2022. The new revenue is based on a return on equity of 9.2% and a capital structure of 50.3% equity and 49.7% debt. SSIR On September 11, 2020, in accordance with the final Order from an earlier rate review filed on February 1, 2019, Colorado Gas filed a SSIR proposal with the CPUC that would recover safety and integrity focused investments in its system for five years. On July 6, 2021, Colorado Gas received approval from the CPUC for its SSIR proposal that will recover safety and integrity focused system investments for three years effective January 1, 2022. The return on SSIR investments will be the current weighted-average cost of long-term debt. Iowa Gas Rate Review On June 1, 2021, Iowa Gas filed a rate review with the IUB seeking recovery of significant infrastructure investments in its 5,000-mile natural gas pipeline system. The rate review requests shifting $2.2 million of rider revenue to base rates and $8.3 million in additional new annual revenue with a capital structure of 50% equity and 50% debt and a return on equity of 10.15%. Iowa statute allows implementation of interim rates 10 days after filing a rate review and Iowa Gas implemented interim rates effective on June 11, 2021. The request seeks to finalize rates in the first quarter of 2022. Kansas Gas Rate Review On May 7, 2021, Kansas Gas filed a rate review and rider renewal with the KCC seeking recovery of significant infrastructure investments in its 4,600-mile natural gas pipeline system. On October 8, 2021, Kansas Gas reached a Global Settlement agreement with KCC Staff and various intervenors for a general rate increase and renewal of its safety and integrity rider. The settlement agreement is subject to review and approval by the KCC. If approved, the settlement will shift $6.6 million of rider revenue to base rates, which are expected to be effective January 1, 2022, and also allow rider renewal for at least five Nebraska Gas Jurisdictional Consolidation and Rate Review On January 26, 2021, Nebraska Gas received approval from the NPSC to consolidate rate schedules into a new, single statewide structure and recover infrastructure investments in its 13,000-mile natural gas pipeline system. Final rates were enacted on March 1, 2021, which replaced interim rates effective September 1, 2020. The approval shifted $4.6 million of SSIR revenue to base rates and is expected to generate $6.5 million in new annual revenue with a capital structure of 50% equity and 50% debt and an authorized return on equity of 9.5%. The approval also includes an extension of the SSIR for five years and an expansion of this mechanism across the consolidated jurisdictions.

Commitments, Contingencies and

Commitments, Contingencies and Guarantees:	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments, Contingencies and Guarantees	Commitments, Contingencies and Guarantees There have been no significant changes to commitments, contingencies and guarantees from those previously disclosed in Note 3 of our Notes to the Consolidated Financial Statements in our 2020 Annual Report on Form 10-K except for those described below. Power Purchase Agreement - Colorado Electric Renewable Advantage On February 19, 2021, Colorado Electric entered into a PPA with TC Colorado Solar, LLC to purchase up to 200 MW of renewable energy upon construction of a new solar facility, to be owned by TC Colorado Solar, LLC, which is expected to be completed by the end of 2023. This agreement will expire 15 years after construction completion. The solar project represents Colorado Electric’s preferred bid in a competitive solicitation process completed in September 2020 through its Renewable Advantage plan.

Revenue_

Revenue:	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Revenue	RevenueOur revenue contracts generally provide for performance obligations that are: fulfilled and transfer control to customers over time; represent a series of distinct services that are substantially the same; involve the same pattern of transfer to the customer; and provide a right to consideration from our customers in an amount that corresponds directly with the value to the customer for the performance completed to date. Therefore, we recognize revenue in the amount to which we have a right to invoice. The following tables depict the disaggregation of revenue, including intercompany revenue, from contracts with customers by customer type and timing of revenue recognition for each of the reportable segments for the three and nine months ended September 30, 2021 and 2020. Sales tax and other similar taxes are excluded from revenues. Three Months Ended September 30, 2021 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 179,982 $ 115,908 $ — $ 15,814 $ (8,846) $ 302,858 Transportation — 37,651 — — (110) 37,541 Wholesale 3,856 — 26,058 — (23,725) 6,189 Market - off-system sales 15,149 75 — — (1,638) 13,586 Transmission/Other 13,913 9,863 — — (5,297) 18,479 Revenue from contracts with customers $ 212,900 $ 163,497 $ 26,058 $ 15,814 $ (39,616) $ 378,653 Other revenues 203 1,186 462 574 (488) 1,937 Total revenues $ 213,103 $ 164,683 $ 26,520 $ 16,388 $ (40,104) $ 380,590 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 15,814 $ (8,846) $ 6,968 Services transferred over time 212,900 163,497 26,058 — (30,770) 371,685 Revenue from contracts with customers $ 212,900 $ 163,497 $ 26,058 $ 15,814 $ (39,616) $ 378,653 Three Months Ended September 30, 2020 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer Types: (in thousands) Retail $ 169,505 $ 94,367 $ — $ 14,668 $ (8,100) $ 270,440 Transportation — 38,196 — — (139) 38,057 Wholesale 5,925 — 26,049 — (24,521) 7,453 Market - off-system sales 9,535 36 — — (1,904) 7,667 Transmission/Other 15,653 10,277 — — (5,235) 20,695 Revenue from contracts with customers $ 200,618 $ 142,876 $ 26,049 $ 14,668 $ (39,899) $ 344,312 Other revenues 224 1,053 469 568 (36) 2,278 Total Revenues $ 200,842 $ 143,929 $ 26,518 $ 15,236 $ (39,935) $ 346,590 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 14,668 $ (8,100) $ 6,568 Services transferred over time 200,618 142,876 26,049 — (31,799) 337,744 Revenue from contracts with customers $ 200,618 $ 142,876 $ 26,049 $ 14,668 $ (39,899) $ 344,312 Nine Months Ended September 30, 2021 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 536,952 $ 601,358 $ — $ 43,751 $ (23,093) $ 1,158,968 Transportation — 117,251 — — (329) 116,922 Wholesale 12,788 — 79,662 — (71,656) 20,794 Market - off-system sales 31,746 235 — — (6,197) 25,784 Transmission/Other 41,339 29,378 — — (15,892) 54,825 Revenue from contracts with customers $ 622,825 $ 748,222 $ 79,662 $ 43,751 $ (117,167) $ 1,377,293 Other revenues 2,619 5,030 1,369 1,738 (1,455) 9,301 Total revenues $ 625,444 $ 753,252 $ 81,031 $ 45,489 $ (118,622) $ 1,386,594 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 43,751 $ (23,093) $ 20,658 Services transferred over time 622,825 748,222 79,662 — (94,074) 1,356,635 Revenue from contracts with customers $ 622,825 $ 748,222 $ 79,662 $ 43,751 $ (117,167) $ 1,377,293 Nine Months Ended September 30, 2020 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer Types: (in thousands) Retail $ 459,949 $ 513,208 $ — $ 43,917 $ (23,855) $ 993,219 Transportation — 113,096 — — (416) 112,680 Wholesale 14,947 — 77,234 — (72,609) 19,572 Market - off-system sales 17,940 197 — — (6,123) 12,014 Transmission/Other 43,271 32,038 — — (14,080) 61,229 Revenue from contracts with customers $ 536,107 $ 658,539 $ 77,234 $ 43,917 $ (117,083) $ 1,198,714 Other revenues 2,074 7,273 1,372 1,940 (819) 11,840 Total Revenues $ 538,181 $ 665,812 $ 78,606 $ 45,857 $ (117,902) $ 1,210,554 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 43,917 $ (23,855) $ 20,062 Services transferred over time 536,107 658,539 77,234 — (93,228) 1,178,652 Revenue from contracts with customers $ 536,107 $ 658,539 $ 77,234 $ 43,917 $ (117,083) $ 1,198,714 Contract Balances The nature of our primary revenue contracts provides an unconditional right to consideration upon service delivery; therefore, no customer contract assets or liabilities exist. The unconditional right to consideration is represented by the balance in our Accounts Receivable further discussed in Note 13

Financing_

Financing:	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Financing	Financing Short-term Debt We had the following Notes payable outstanding in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2021 December 31, 2020 Balance Outstanding Letters of Credit (a) Balance Outstanding Letters of Credit (a) Revolving Credit Facility — 23,255 — 24,730 CP Program 332,525 — 234,040 — Total Notes payable $ 332,525 $ 23,255 $ 234,040 $ 24,730 _______________ (a) Letters of credit are off-balance sheet commitments that reduce the borrowing capacity available on our corporate Revolving Credit Facility. Revolving Credit Facility and CP Program On July 19, 2021, we amended and restated our corporate Revolving Credit Facility, maintaining total commitments of $750 million and extending the term through July 19, 2026 with two one year extension options (subject to consent from lenders). This facility is similar to the former revolving credit facility, which includes an accordion feature that allows us, with the consent of the administrative agent, the issuing agents and each bank increasing or providing a new commitment, to increase total commitments up to $1.0 billion. Borrowings continue to be available under a base rate or various Eurodollar rate options. Based on our current credit ratings, the margins for base rate borrowings, Eurodollar borrowings and letters of credit will be 0.125%, 1.125% and 1.125%, respectively, and a 0.175% commitment fee will be charged on unused amounts. Our net short-term borrowings related to our Revolving Credit Facility and CP Program during the nine months ended September 30, 2021 were $98.5 million. The weighted average interest rate on short-term borrowings related to our Revolving Credit Facility and CP Program at September 30, 2021 was 0.19%. Term Loan On February 24, 2021, we entered into a nine-month, $800 million unsecured term loan to provide additional liquidity and to meet our cash needs related to the incremental fuel, purchased power and natural gas costs from Winter Storm Uri. The term loan, carried no prepayment penalty and was subject to the same covenant requirements as our Revolving Credit Facility. We repaid $200 million of this term loan in the first quarter of 2021. Proceeds from the August 26, 2021 public debt offering (discussed below) were used to repay the remaining balance on this term loan. Long-term Debt On August 26, 2021, we completed a public debt offering which consisted of $600 million, 1.037% three year senior unsecured notes due August 23, 2024. The notes include an optional redemption provision and may be redeemed, in whole or in part, without premium, on or after February 23, 2022. The proceeds from the offering, which were net of $3.7 million of deferred financing costs, were used to repay amounts outstanding under our term loan entered into on February 24, 2021. Debt Covenants Under our Revolving Credit Facility, we are required to maintain a Consolidated Indebtedness to Capitalization Ratio not to exceed 0.65 to 1.00. Our Consolidated Indebtedness to Capitalization Ratio was calculated by dividing (i) consolidated indebtedness, which includes letters of credit and certain guarantees issued, by (ii) capital, which includes consolidated indebtedness plus consolidated net worth, which excludes non-controlling interest in subsidiaries. Subject to applicable cure periods, a violation of any of these covenants would constitute an event of default that entitles the lenders to terminate their remaining commitments and accelerate all principal and interest outstanding. Our Revolving Credit Facility and term loans require compliance with the following financial covenant, which we were in compliance with at September 30, 2021: As of September 30, 2021 Covenant Requirement Consolidated Indebtedness to Capitalization Ratio 62.4% Less than 65% Equity At-the-Market Equity Offering Program During the three months ended September 30, 2021, we issued a total of 0.3 million shares of common stock under the ATM for proceeds of $23 million, net of $0.2 million in issuance costs. During the nine months ended September 30, 2021, we issued a total of 0.9 million shares of common stock under the ATM for proceeds of $63 million, net of $0.6 million in issuance costs.

Earnings Per Share_

Earnings Per Share:	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share A reconciliation of share amounts used to compute earnings per share in the accompanying Condensed Consolidated Statements of Income was as follows (in thousands, except per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net income available for common stock $ 44,112 $ 36,283 $ 165,589 $ 150,423 Weighted average shares - basic 63,341 62,575 62,950 62,310 Dilutive effect of: Equity compensation 95 55 96 52 Weighted average shares - diluted 63,436 62,630 63,046 62,362 Earnings per share of common stock: Earnings per share, Basic $ 0.70 $ 0.58 $ 2.63 $ 2.41 Earnings per share, Diluted $ 0.70 $ 0.58 $ 2.63 $ 2.41 The following securities were excluded from the diluted earnings per share computation because of their anti-dilutive nature (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Equity compensation 9 22 12 22 Restricted stock — 49 1 40 Anti-dilutive shares 9 71 13 62

Risk Management and Derivatives

Risk Management and Derivatives:	9 Months Ended
	Sep. 30, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Risk Management and Derivatives	Risk Management and Derivatives Market and Credit Risk Disclosures Our activities in the regulated and non-regulated energy sectors expose us to a number of risks in the normal operations of our businesses. Depending on the activity, we are exposed to varying degrees of market risk and credit risk. Market Risk Market risk is the potential loss that may occur as a result of an adverse change in market price, rate or supply. We are exposed to the following market risks, including, but not limited to: • Commodity price risk associated with our retail natural gas and wholesale electric power marketing activities, as well as our fuel procurement for several of our gas-fired generation assets, which include market fluctuations due to unpredictable factors such as weather (Winter Storm Uri), market speculation, pipeline constraints, and other factors that may impact natural gas and electric energy supply and demand; and • Interest rate risk associated with future debt, including reduced access to liquidity during periods of extreme capital markets volatility, such as the 2008 financial crisis and the COVID-19 pandemic. Credit Risk Credit risk is the risk of financial loss resulting from non-performance of contractual obligations by a counterparty. We attempt to mitigate our credit exposure by conducting business primarily with high credit quality entities, setting tenor and credit limits commensurate with counterparty financial strength, obtaining master netting agreements and mitigating credit exposure with less creditworthy counterparties through parental guarantees, cash collateral requirements, letters of credit and other security agreements. We perform ongoing credit evaluations of our customers and adjust credit limits based upon payment history and the customers’ current creditworthiness, as determined by review of their current credit information. We maintain a provision for estimated credit losses based upon historical experience, changes in current market conditions, expected losses and any specific customer collection issue that is identified. Derivatives and Hedging Activity Our derivative and hedging activities included in the accompanying Condensed Consolidated Balance Sheets, Condensed Consolidated Statements of Income and Condensed Consolidated Statements of Comprehensive Income are detailed below and in Note 8 . The operations of our utilities, including natural gas sold by our Gas Utilities and natural gas used by our Electric Utilities’ generating facilities or those facilities under PPAs where our Electric Utilities must provide the generation fuel (tolling agreements), expose our utility customers to natural gas price volatility. Therefore, as allowed or required by state regulatory commissions, we have entered into commission-approved hedging programs utilizing natural gas futures, options, over-the-counter swaps and basis swaps to reduce our customers’ underlying exposure to these fluctuations. These transactions are considered derivatives and in accordance with accounting standards for derivatives and hedging, mark-to-market adjustments are recorded as Derivative assets or Derivative liabilities on the accompanying Condensed Consolidated Balance Sheets, net of balance sheet offsetting as permitted by GAAP. For our regulated Utilities’ hedging plans, unrealized and realized gains and losses, as well as option premiums and commissions on these transactions, are recorded as Regulatory assets or Regulatory liabilities in the accompanying Condensed Consolidated Balance Sheets in accordance with the state regulatory commission guidelines. When the related costs are recovered through our rates, the hedging activity is recognized in the Condensed Consolidated Statements of Income. We periodically use wholesale power purchase and sale contracts to manage purchased power costs and load requirements associated with serving our electric customers that are considered derivative instruments due to not qualifying for the normal purchases and normal sales exception to derivative accounting. Changes in the fair value of these commodity derivatives are recognized in the Condensed Consolidated Statements of Income. We buy, sell and deliver natural gas at competitive prices by managing commodity price risk. As a result of these activities, this area of our business is exposed to risks associated with changes in the market price of natural gas. We manage our exposure to such risk using over-the-counter and exchange traded options and swaps with counterparties in anticipation of forecasted purchases and sales during time frames ranging from October 2021 through August 2024. A portion of our over-the-counter swaps have been designated as cash flow hedges to mitigate the commodity price risk associated with deliveries under fixed price forward contracts to deliver gas to our Choice Gas Program customers. The gain or loss on these designated derivatives is reported in AOCI in the accompanying Condensed Consolidated Balance Sheets and reclassified into earnings in the same period that the underlying hedged item is recognized in earnings. Effectiveness of our hedging position is evaluated at least quarterly. The contract or notional amounts and terms of the electric and natural gas derivative commodity instruments held at our Utilities are composed of both long and short positions. We had the following net long positions as of: September 30, 2021 December 31, 2020 Units Notional Maximum Term (months) (a) Notional Maximum Term (months) (a) Natural gas futures purchased MMBtus 1,700,000 6 620,000 3 Natural gas options purchased, net MMBtus 8,420,000 6 3,160,000 3 Natural gas basis swaps purchased MMBtus 1,500,000 6 900,000 3 Natural gas over-the-counter swaps, net (b) MMBtus 5,920,000 35 3,850,000 17 Natural gas physical contracts, net (c) MMBtus 18,758,835 7 17,513,061 22 Electric wholesale contracts (c) MWh 65,625 3 219,000 12 __________ (a) Term reflects the maximum forward period hedged. (b) As of September 30, 2021, 2,700,000 MMBtus of natural gas over-the-counter swaps purchases were designated as cash flow hedges. (c) Volumes exclude derivative contracts that qualify for the normal purchases and normal sales exception permitted by GAAP. We have certain derivative contracts which contain credit provisions. These credit provisions may require the Company to post collateral when credit exposure to the Company is in excess of a negotiated line of unsecured credit. At September 30, 2021, the Company posted $0.9 million related to such provisions, which is included in Other current assets on the Condensed Consolidated Balance Sheets. Derivatives by Balance Sheet Classification As required by accounting standards for derivatives and hedges, fair values within the following tables are presented on a gross basis aside from the netting of asset and liability positions. Netting of positions is permitted in accordance with accounting standards for offsetting and under terms of our master netting agreements. The following table presents the fair value and balance sheet classification of our derivative instruments (in thousands) as of: Balance Sheet Location September 30, 2021 December 31, 2020 Derivatives designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 6,989 $ 181 Noncurrent commodity derivatives Other assets, non-current 32 43 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current — (108) Total derivatives designated as hedges $ 7,021 $ 116 Derivatives not designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 5,327 $ 1,667 Noncurrent commodity derivatives Other assets, non-current 1,580 151 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current (3,471) (1,936) Total derivatives not designated as hedges $ 3,436 $ (118) Derivatives Designated as Hedge Instruments The impacts of cash flow hedges on our Condensed Consolidated Statements of Comprehensive Income and Condensed Consolidated Statements of Income are presented below for the three and nine months ended September 30, 2021 and 2020. Note that this presentation does not reflect gains or losses arising from the underlying physical transactions; therefore, it is not indicative of the economic profit or loss we realized when the underlying physical and financial transactions were settled. Three Months Ended September 30, Three Months Ended September 30, 2021 2020 2021 2020 Derivatives in Cash Flow Hedging Relationships Amount of Gain/(Loss) Recognized in OCI Income Statement Location Amount of Gain/(Loss) Reclassified from AOCI into Income (in thousands) (in thousands) Interest rate swaps $ 712 $ 712 Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) $ (712) $ (712) Commodity derivatives 5,536 691 Fuel, purchased power and cost of natural gas sold 331 (178) Total $ 6,248 $ 1,403 $ (381) $ (890) Nine Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Derivatives in Cash Flow Hedging Relationships Amount of Gain/(Loss) Recognized in OCI Income Statement Location Amount of Gain/(Loss) Reclassified from AOCI into Income (in thousands) (in thousands) Interest rate swaps $ 2,138 $ 2,138 Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) $ (2,138) $ (2,138) Commodity derivatives 6,896 959 Fuel, purchased power and cost of natural gas sold 356 (734) Total $ 9,034 $ 3,097 $ (1,782) $ (2,872) As of September 30, 2021, $4.0 million of net gains related to our interest rate swaps and commodity derivatives are expected to be reclassified from AOCI into earnings as gains within the next 12 months. As market prices fluctuate, estimated and actual realized gains or losses will change during future periods. Derivatives Not Designated as Hedge Instruments The following table summarizes the impacts of derivative instruments not designated as hedge instruments on our Condensed Consolidated Statements of Income for the three and nine months ended September 30, 2021 and 2020. Note that this presentation does not reflect gains or losses arising from the underlying physical transactions; therefore, it is not indicative of the economic profit or loss we realized when the underlying physical and financial transactions were settled. Three Months Ended September 30, 2021 2020 Derivatives Not Designated as Hedging Instruments Location of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income (in thousands) Commodity derivatives - Electric Fuel, purchased power and cost of natural gas sold $ 2,494 $ (1,386) Commodity derivatives - Natural Gas Fuel, purchased power and cost of natural gas sold 4,004 1,777 $ 6,498 $ 391 Nine Months Ended September 30, 2021 2020 Derivatives Not Designated as Hedging Instruments Location of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income (in thousands) Commodity derivatives - Electric Fuel, purchased power and cost of natural gas sold $ (2,628) $ (228) Commodity derivatives - Natural Gas Fuel, purchased power and cost of natural gas sold 6,186 2,992 $ 3,558 $ 2,764 As discussed above, financial instruments used in our regulated Gas Utilities are not designated as cash flow hedges. There is no earnings impact because the unrealized gains and losses arising from the use of these financial instruments are recorded as Regulatory assets or Regulatory liabilities. The net unrealized (losses) or gains included in our Regulatory asset or Regulatory liability related to the hedges in our Gas Utilities were $13.2 million and $(2.2) million as of September 30, 2021 and December 31, 2020, respectively. For our Electric Utilities, the unrealized gains and losses arising from these derivatives are recognized in the Condensed Consolidated Statements of Income.

Fair Value Measurements_

Fair Value Measurements:	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurement	Fair Value Measurements We use the following fair value hierarchy for determining inputs for our financial instruments. Our assets and liabilities for financial instruments are classified and disclosed in one of the following fair value categories: Level 1 — Unadjusted quoted prices available in active markets that are accessible at the measurement date for identical unrestricted assets or liabilities. Level 1 instruments primarily consist of highly liquid and actively traded financial instruments with quoted pricing information on an ongoing basis. Level 2 — Pricing inputs include quoted prices for identical or similar assets and liabilities in active markets other than quoted prices in Level 1, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability and inputs that are derived principally from or corroborated by observable market data by correlation or other means. Level 3 — Pricing inputs are generally less observable from objective sources. These inputs reflect management’s best estimate of fair value using its own assumptions about the assumptions a market participant would use in pricing the asset or liability. Assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement requires judgment and may affect the placement within the fair value hierarchy levels. We record transfers, if necessary, between levels at the end of the reporting period for all of our financial instruments. Transfers into Level 3, if any, occur when significant inputs used to value the derivative instruments become less observable, such as a significant decrease in the frequency and volume in which the instrument is traded, negatively impacting the availability of observable pricing inputs. Transfers out of Level 3, if any, occur when the significant inputs become more observable, such as when the time between the valuation date and the delivery date of a transaction becomes shorter, positively impacting the availability of observable pricing inputs. Recurring Fair Value Measurements Derivatives The commodity contracts for our Utilities segments are valued using the market approach and include forward strip pricing at liquid delivery points, exchange-traded futures, options, basis swaps and over-the-counter swaps and options (Level 2) for wholesale electric energy and natural gas contracts. For exchange-traded futures, options and basis swap assets and liabilities, fair value was derived using broker quotes validated by the exchange settlement pricing for the applicable contract. For over-the-counter instruments, the fair value is obtained by utilizing a nationally recognized service that obtains observable inputs to compute the fair value, which we validate by comparing our valuation with the counterparty. The fair value of these swaps includes a CVA based on the credit spreads of the counterparties when we are in an unrealized gain position or on our own credit spread when we are in an unrealized loss position. For additional information, see Note 1 of our Notes to the Consolidated Financial Statements in our 2020 Annual Report on Form 10-K. As of September 30, 2021 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting (a) Total (in thousands) Assets: Commodity derivatives — Gas Utilities $ — $ 32,298 $ — $ (18,370) $ 13,928 Commodity derivatives — Electric Utilities $ — $ — $ — $ — $ — Total $ — $ 32,298 $ — $ (18,370) $ 13,928 Liabilities: Commodity derivatives — Gas Utilities $ — $ 1,128 $ — $ (141) $ 987 Commodity derivatives — Electric Utilities $ — $ 2,484 $ — $ — $ 2,484 Total $ — $ 3,612 $ — $ (141) $ 3,471 __________ (a) As of September 30, 2021, $18 million of our commodity derivative assets and $0.1 million of our commodity derivative liabilities, as well as related collateral amounts, were subject to master netting agreements. Collateral amounts are included in Other current assets on the Condensed Consolidated Balance Sheets. As of December 31, 2020 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting (a) Total (in thousands) Assets: Commodity derivatives — Gas Utilities $ — $ 2,504 $ — $ (1,527) $ 977 Commodity derivatives — Electric Utilities $ — $ 1,065 $ — $ — $ 1,065 Total $ — $ 3,569 $ — $ (1,527) $ 2,042 Liabilities: Commodity derivatives — Gas Utilities $ — $ 2,675 $ — $ (1,552) $ 1,123 Commodity derivatives — Electric Utilities $ — $ 921 $ — $ — $ 921 Total $ — $ 3,596 $ — $ (1,552) $ 2,044 __________ (a) As of December 31, 2020, $1.5 million of our commodity derivative assets and $1.6 million of our commodity derivative liabilities, as well as related collateral amounts, were subject to master netting agreements. Collateral amounts are included in Other current assets on the Condensed Consolidated Balance Sheets. Pension and Postretirement Plan Assets Fair value measurements also apply to the valuation of our pension and postretirement plan assets. Current accounting guidance requires employers to annually disclose information about the fair value measurements of their assets of a defined benefit pension or other postretirement plan. The fair value of these assets is presented in Note 15 to the Consolidated Financial Statements included in our 2020 Annual Report on Form 10-K. Other fair value measures The carrying amount of cash and cash equivalents, restricted cash and equivalents, and short-term borrowings approximates fair value due to their liquid or short-term nature. Cash, cash equivalents, and restricted cash are classified in Level 1 in the fair value hierarchy. Notes payable consist of commercial paper borrowings and since these borrowings are not traded on an exchange, they are classified in Level 2 in the fair value hierarchy. The following table presents the carrying amounts and fair values of financial instruments not recorded at fair value on the Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2021 December 31, 2020 Carrying Fair Value Carrying Fair Value Long-term debt, including current maturities (a) $ 4,125,571 $ 4,614,244 $ 3,536,536 $ 4,208,167 __________ (a) Long-term debt is valued based on observable inputs available either directly or indirectly for similar liabilities in active markets and therefore is classified as Level 2 in the fair value hierarchy. Carrying amount of long-term debt is net of deferred financing costs.

Other Comprehensive Income_

Other Comprehensive Income:	9 Months Ended
	Sep. 30, 2021
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income	Other Comprehensive Income We record deferred gains (losses) in AOCI related to interest rate swaps designated as cash flow hedges, commodity contracts designated as cash flow hedges and the amortization of components of our defined benefit plans. Deferred gains (losses) for our commodity contracts designated as cash flow hedges are recognized in earnings upon settlement, while deferred gains (losses) related to our interest rate swaps are recognized in earnings as they are amortized. The following table details reclassifications out of AOCI and into Net income. The amounts in parentheses below indicate decreases to Net income in the Condensed Consolidated Statements of Income for the period (in thousands): Location on the Condensed Consolidated Statements of Income Amount Reclassified from AOCI Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Gains and (losses) on cash flow hedges: Interest rate swaps Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) $ (712) $ (712) $ (2,138) $ (2,138) Commodity contracts Fuel, purchased power and cost of natural gas sold 331 (178) 356 (734) (381) (890) (1,782) (2,872) Income tax Income tax (expense) (26) 209 308 680 Total reclassification adjustments related to cash flow hedges, net of tax $ (407) $ (681) $ (1,474) $ (2,192) Amortization of components of defined benefit plans: Prior service cost Operations and maintenance $ 25 $ 24 $ 74 $ 79 Actuarial gain (loss) Operations and maintenance (598) (597) (1,793) (1,791) (573) (573) (1,719) (1,712) Income tax Income tax (expense) 133 143 492 407 Total reclassification adjustments related to defined benefit plans, net of tax $ (440) $ (430) $ (1,227) $ (1,305) Total reclassifications $ (847) $ (1,111) $ (2,701) $ (3,497) Balances by classification included within AOCI, net of tax on the accompanying Condensed Consolidated Balance Sheets were as follows (in thousands): Derivatives Designated as Cash Flow Hedges Interest Rate Swaps Commodity Derivatives Employee Benefit Plans Total As of December 31, 2020 $ (12,558) $ 2 $ (14,790) $ (27,346) Other comprehensive income (loss) before reclassifications — 5,476 — 5,476 Amounts reclassified from AOCI 1,743 (269) 1,227 2,701 As of September 30, 2021 $ (10,815) $ 5,209 $ (13,563) $ (19,169) Derivatives Designated as Cash Flow Hedges Interest Rate Swaps Commodity Derivatives Employee Benefit Plans Total As of December 31, 2019 $ (15,122) $ (456) $ (15,077) $ (30,655) Other comprehensive income (loss) before reclassifications — 181 55 236 Amounts reclassified from AOCI 1,630 562 1,305 3,497 As of September 30, 2020 $ (13,492) $ 287 $ (13,717) $ (26,922)

Employee Benefit Plans_

Employee Benefit Plans:	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans Defined Benefit Pension Plan The components of net periodic benefit cost for the Defined Benefit Pension Plan were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Service cost $ 1,260 $ 1,352 $ 3,779 $ 4,058 Interest cost 2,328 3,356 6,984 10,069 Expected return on plan assets (5,219) (5,647) (15,657) (16,943) Net loss 1,828 2,093 5,486 6,279 Net periodic benefit cost $ 197 $ 1,154 $ 592 $ 3,463 Defined Benefit Postretirement Healthcare Plan The components of net periodic benefit cost for the Defined Benefit Postretirement Healthcare Plan were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Service cost $ 560 $ 514 $ 1,678 $ 1,542 Interest cost 264 412 793 1,237 Expected return on plan assets (34) (46) (102) (137) Prior service cost (benefit) (108) (136) (326) (410) Net loss 116 5 350 15 Net periodic benefit cost $ 798 $ 749 $ 2,393 $ 2,247 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans The components of net periodic benefit cost for the Supplemental Non-qualified Defined Benefit and Defined Contribution Plans were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Service cost $ 235 $ 1,035 $ 1,948 $ 1,482 Interest cost 176 274 530 824 Prior service cost — 1 — 1 Net loss 439 425 1,316 1,277 Net periodic benefit cost $ 850 $ 1,735 $ 3,794 $ 3,584 Contributions Contributions to the Defined Benefit Pension Plan are cash contributions made directly to the Pension Plan Trust account. Contributions to the Postretirement Healthcare and Supplemental Plans are made in the form of benefit payments. Contributions made in the first nine months of 2021 and anticipated contributions for 2021 and 2022 are as follows (in thousands): Contributions Made Additional Contributions Contributions Nine Months Ended September 30, 2021 Anticipated for 2021 Anticipated for 2022 Defined Benefit Pension Plan $ — $ — $ 3,900 Non-pension Defined Benefit Postretirement Healthcare Plan $ 4,145 $ 1,382 $ 5,202 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans $ 1,445 $ 482 $ 2,149

Income Taxes_

Income Taxes:	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Winter Storm Uri As discussed in Note 2 above, our Utilities submitted cost recovery applications which seek to recover incremental costs from Winter Storm Uri through a regulatory mechanism. We expect to recover these costs from customers over several years. Winter Storm Uri costs, which will be deductible in our 2021 tax return, created a net deferred tax liability of approximately $130 million. The deferred tax liability will reverse with the same timing as the costs are recovered from our customers. The income tax deduction recognized from Winter Storm Uri will create a NOL in our 2021 federal and state income tax returns. Our federal NOL carryforwards no longer expire due to the TCJA; however, our state NOL carryforwards expire at various dates from 2021 to 2041. We do not anticipate material changes to our valuation allowance against the state NOL carryforwards from Winter Storm Uri. Therefore, we did not record an additional valuation allowance against the state NOL carryforwards as of September 30, 2021. Income Tax (Expense) and Effective Tax Rates Three Months Ended September 30, 2021 Compared to the Three Months Ended September 30, 2020 Income tax (expense) and the effective tax rate were comparable to the same period in the prior year. Nine Months Ended September 30, 2021 Compared to the Nine Months Ended September 30, 2020 Income tax (expense) for the nine months ended September 30, 2021 was $(6.3) million compared to $(25) million reported for the same period in 2020. For the nine months ended September 30, 2021, the effective tax rate was 3.5% compared to 13.6% for the same period in 2020. The lower effective tax rate is primarily due to $10 million of increased tax benefits from Colorado Electric and Nebraska Gas TCJA-related bill credits to customers (which is offset by reduced revenue), $3.2 million of increased tax benefits from federal production tax credits associated with new wind assets, $2.2 million of increased tax benefits from amortization of excess deferred income taxes, $1.9 million of tax benefits from various statutory rate changes and $1.1 million of increased flow-through tax benefits related to repairs and certain indirect costs. These current year tax benefits were partially offset by a prior year tax benefit from the reversal of accrued excess deferred income taxes as part of resolving the last of the Company’s open dockets seeking approval of its TCJA plans.

Business Segment Information_

Business Segment Information:	9 Months Ended
	Sep. 30, 2021
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. Accounting standards for presentation of segments require an approach based on the way we organize the segments for making operating decisions and how the CODM assesses performance. The CODM assesses the performance of our segments using adjusted operating income, which recognizes intersegment revenues, costs, and assets 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 information was as follows (in thousands): Total assets (net of intercompany eliminations) as of: September 30, 2021 December 31, 2020 Electric Utilities $ 3,267,074 $ 3,120,928 Gas Utilities 5,052,898 4,376,204 Power Generation 398,915 404,220 Mining 76,791 77,085 Corporate and Other 114,712 110,349 Total assets $ 8,910,390 $ 8,088,786 Three Months Ended September 30, 2021 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 207,374 $ 203 $ 5,526 $ — $ 213,103 Gas Utilities 161,977 1,087 1,520 99 164,683 Power Generation 2,333 412 23,725 50 26,520 Mining 6,969 235 8,845 339 16,388 Inter-company eliminations — — (39,616) (488) (40,104) Total $ 378,653 $ 1,937 $ — $ — $ 380,590 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 Nine Months Ended September 30, 2021 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 604,966 $ 2,619 $ 17,859 $ — $ 625,444 Gas Utilities 743,663 4,745 4,559 285 753,252 Power Generation 8,006 1,219 71,656 150 81,031 Mining 20,658 718 23,093 1,020 45,489 Inter-company eliminations — — (117,167) (1,455) (118,622) Total $ 1,377,293 $ 9,301 $ — $ — $ 1,386,594 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 Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Adjusted operating income: Electric Utilities $ 57,608 $ 52,083 $ 114,989 $ 121,726 Gas Utilities 17,257 18,147 139,336 139,253 Power Generation 10,323 8,738 32,842 31,489 Mining 4,908 3,505 11,813 9,992 Corporate and Other (223) (239) (3,526) (108) Operating income 89,873 82,234 295,454 302,352 Interest expense, net (38,018) (36,041) (113,820) (107,039) Impairment of investment — — — (6,859) Other income (expense), net 1,560 (1,193) 1,635 (703) Income tax (expense) (5,253) (4,651) (6,333) (25,484) Net income 48,162 40,349 176,936 162,267 Net income attributable to non-controlling interest (4,050) (4,066) (11,347) (11,844) Net income available for common stock $ 44,112 $ 36,283 $ 165,589 $ 150,423

Selected Balance Sheet Informat

Selected Balance Sheet Information:	9 Months Ended
	Sep. 30, 2021
Selected Balance Sheet Information [Abstract]
Selected Balance Sheet Information	Selected Balance Sheet Information Accounts Receivable and Allowance for Credit Losses Following is a summary of Accounts receivable, net included in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2021 December 31, 2020 Accounts receivable, trade $ 120,930 $ 146,899 Unbilled revenue 63,338 126,065 Less: Allowance for credit losses (2,312) (7,003) Accounts receivable, net $ 181,956 $ 265,961 Changes to allowance for credit losses for the nine months ended September 30, 2021 and 2020, respectively, were as follows (in thousands): Balance at Beginning of Year Additions Charged to Costs and Expenses Recoveries and Other Additions Write-offs and Other Deductions Balance at September 30, 2021 $ 7,003 $ 1,111 $ 2,420 $ (8,222) $ 2,312 2020 $ 2,444 $ 8,471 $ 3,720 $ (6,026) $ 8,609 Materials, Supplies and Fuel The following amounts by major classification are included in Materials, supplies and fuel on the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2021 December 31, 2020 Materials and supplies $ 85,612 $ 85,250 Fuel - Electric Utilities 1,240 1,531 Natural gas in storage 58,891 30,619 Total materials, supplies and fuel $ 145,743 $ 117,400 Accrued Liabilities The following amounts by major classification are included in Accrued liabilities on the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2021 December 31, 2020 Accrued employee compensation, benefits and withholdings $ 72,328 $ 77,806 Accrued property taxes 44,231 47,105 Customer deposits and prepayments 53,652 52,185 Accrued interest 46,532 31,520 Other (none of which is individually significant) 33,092 34,996 Total accrued liabilities $ 249,835 $ 243,612

Subsequent Events_

Subsequent Events:	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events We evaluated all subsequent event activity and concluded that no subsequent events have occurred that would require recognition in the condensed consolidated financial statements or disclosures, with the exception of Colorado Gas, Kansas Gas and Wyoming Gas regulatory activity disclosed in Note 2 .

Management's Statement (Policie

Management's Statement (Policies)	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Segment Reporting	Segment Reporting We conduct our operations through the following reportable segments: Electric Utilities, Gas Utilities, Power Generation and Mining. 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.
Use of Estimates and Basis of Presentation	Use of Estimates and Basis of Presentation The information furnished in the accompanying Condensed Consolidated Financial Statements reflects certain estimates required and all adjustments, including accruals, which are, in the opinion of management, necessary for a fair presentation of the September 30, 2021, December 31, 2020 and September 30, 2020 financial information. Certain lines of business in which we operate are highly seasonal, and our interim results of operations are not necessarily indicative of the results of operations to be expected for an entire year.
Recently Issued and Adopted Accounting Standards	Recently Issued Accounting Standards Facilitation of the Effects of Reference Rate Reform on Financial Reporting, ASU 2020-04 In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which was subsequently amended by ASU 2021-01. The standard provides relief for companies preparing for discontinuation of interest rates, such as LIBOR, and allows optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions affected by reference rate reform if certain criteria are met. The amendments in this update are elective and are effective upon the ASU issuance through December 31, 2022. We are currently evaluating whether we will apply the optional guidance as we assess the impact of the discontinuance of LIBOR on our current arrangements and the potential impact on our financial position, results of operations and cash flows. Recently Adopted Accounting Standards Simplifying the Accounting for Income Taxes, ASU 2019-12 In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes as part of its overall simplification initiative to reduce costs and complexity in applying accounting standards while maintaining or improving the usefulness of the information provided to users of the financial statements. Amendments include removal of certain exceptions to the general principles of ASC 740, Income Taxes , and simplification in several other areas such as accounting for a franchise tax (or similar tax) that is partially based on income. We adopted this standard prospectively on January 1, 2021. Adoption of this standard did not have an impact on our financial position, results of operations or cash flows.
Revenue Recognition	Our revenue contracts generally provide for performance obligations that are: fulfilled and transfer control to customers over time; represent a series of distinct services that are substantially the same; involve the same pattern of transfer to the customer; and provide a right to consideration from our customers in an amount that corresponds directly with the value to the customer for the performance completed to date. Therefore, we recognize revenue in the amount to which we have a right to invoice. The nature of our primary revenue contracts provides an unconditional right to consideration upon service delivery; therefore, no customer contract assets or liabilities exist. The unconditional right to consideration is represented by the balance in our Accounts Receivable further discussed in Note 13

Regulatory Matters (Tables)

Regulatory Matters (Tables)	9 Months Ended
	Sep. 30, 2021
Regulatory Assets and Liabilities Disclosure [Abstract]
Schedule of Regulatory Assets and Liabilities	We had the following regulatory assets and liabilities (in thousands): As of As of September 30, 2021 December 31, 2020 Regulatory assets Winter Storm Uri (a) $ 532,766 $ — Deferred energy and fuel cost adjustments (b) 59,741 39,035 Deferred gas cost adjustments (b) 6,076 3,200 Gas price derivatives (b) — 2,226 Deferred taxes on AFUDC (c) 7,537 7,491 Employee benefit plans and related deferred taxes (d) 114,234 116,598 Environmental (b) 1,395 1,413 Loss on reacquired debt (b) 21,460 22,864 Deferred taxes on flow through accounting (d) 54,199 47,515 Decommissioning costs (b) 6,583 8,988 Gas supply contract termination (b) — 2,524 Other regulatory assets (b) 26,064 26,404 Total regulatory assets 830,055 278,258 Less current regulatory assets (213,031) (51,676) Regulatory assets, non-current $ 617,024 $ 226,582 Regulatory liabilities Deferred energy and gas costs (b) $ 9,408 $ 13,253 Gas price derivatives (b) 13,234 — Employee benefit plan costs and related deferred taxes (d) 39,203 40,256 Cost of removal (b) 181,180 172,902 Excess deferred income taxes (d) 266,477 285,259 Other regulatory liabilities (d) 16,915 21,050 Total regulatory liabilities 526,417 532,720 Less current regulatory liabilities (30,156) (25,061) Regulatory liabilities, non-current $ 496,261 $ 507,659 __________ (a) Timing of Winter Storm Uri incremental cost recovery and associated carrying costs are subject to pending applications with our utility commissions. See further information below. (b) Recovery of costs, but we are not allowed a rate of return. (c) In addition to recovery of costs, we are allowed a rate of return. (d) In addition to recovery or repayment of costs, we are allowed a return on a portion of this amount or a reduction in rate base.

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following tables depict the disaggregation of revenue, including intercompany revenue, from contracts with customers by customer type and timing of revenue recognition for each of the reportable segments for the three and nine months ended September 30, 2021 and 2020. Sales tax and other similar taxes are excluded from revenues. Three Months Ended September 30, 2021 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 179,982 $ 115,908 $ — $ 15,814 $ (8,846) $ 302,858 Transportation — 37,651 — — (110) 37,541 Wholesale 3,856 — 26,058 — (23,725) 6,189 Market - off-system sales 15,149 75 — — (1,638) 13,586 Transmission/Other 13,913 9,863 — — (5,297) 18,479 Revenue from contracts with customers $ 212,900 $ 163,497 $ 26,058 $ 15,814 $ (39,616) $ 378,653 Other revenues 203 1,186 462 574 (488) 1,937 Total revenues $ 213,103 $ 164,683 $ 26,520 $ 16,388 $ (40,104) $ 380,590 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 15,814 $ (8,846) $ 6,968 Services transferred over time 212,900 163,497 26,058 — (30,770) 371,685 Revenue from contracts with customers $ 212,900 $ 163,497 $ 26,058 $ 15,814 $ (39,616) $ 378,653 Three Months Ended September 30, 2020 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer Types: (in thousands) Retail $ 169,505 $ 94,367 $ — $ 14,668 $ (8,100) $ 270,440 Transportation — 38,196 — — (139) 38,057 Wholesale 5,925 — 26,049 — (24,521) 7,453 Market - off-system sales 9,535 36 — — (1,904) 7,667 Transmission/Other 15,653 10,277 — — (5,235) 20,695 Revenue from contracts with customers $ 200,618 $ 142,876 $ 26,049 $ 14,668 $ (39,899) $ 344,312 Other revenues 224 1,053 469 568 (36) 2,278 Total Revenues $ 200,842 $ 143,929 $ 26,518 $ 15,236 $ (39,935) $ 346,590 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 14,668 $ (8,100) $ 6,568 Services transferred over time 200,618 142,876 26,049 — (31,799) 337,744 Revenue from contracts with customers $ 200,618 $ 142,876 $ 26,049 $ 14,668 $ (39,899) $ 344,312 Nine Months Ended September 30, 2021 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 536,952 $ 601,358 $ — $ 43,751 $ (23,093) $ 1,158,968 Transportation — 117,251 — — (329) 116,922 Wholesale 12,788 — 79,662 — (71,656) 20,794 Market - off-system sales 31,746 235 — — (6,197) 25,784 Transmission/Other 41,339 29,378 — — (15,892) 54,825 Revenue from contracts with customers $ 622,825 $ 748,222 $ 79,662 $ 43,751 $ (117,167) $ 1,377,293 Other revenues 2,619 5,030 1,369 1,738 (1,455) 9,301 Total revenues $ 625,444 $ 753,252 $ 81,031 $ 45,489 $ (118,622) $ 1,386,594 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 43,751 $ (23,093) $ 20,658 Services transferred over time 622,825 748,222 79,662 — (94,074) 1,356,635 Revenue from contracts with customers $ 622,825 $ 748,222 $ 79,662 $ 43,751 $ (117,167) $ 1,377,293 Nine Months Ended September 30, 2020 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer Types: (in thousands) Retail $ 459,949 $ 513,208 $ — $ 43,917 $ (23,855) $ 993,219 Transportation — 113,096 — — (416) 112,680 Wholesale 14,947 — 77,234 — (72,609) 19,572 Market - off-system sales 17,940 197 — — (6,123) 12,014 Transmission/Other 43,271 32,038 — — (14,080) 61,229 Revenue from contracts with customers $ 536,107 $ 658,539 $ 77,234 $ 43,917 $ (117,083) $ 1,198,714 Other revenues 2,074 7,273 1,372 1,940 (819) 11,840 Total Revenues $ 538,181 $ 665,812 $ 78,606 $ 45,857 $ (117,902) $ 1,210,554 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 43,917 $ (23,855) $ 20,062 Services transferred over time 536,107 658,539 77,234 — (93,228) 1,178,652 Revenue from contracts with customers $ 536,107 $ 658,539 $ 77,234 $ 43,917 $ (117,083) $ 1,198,714

Financing (Tables)

Financing (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Schedule of Short-term Debt	We had the following Notes payable outstanding in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2021 December 31, 2020 Balance Outstanding Letters of Credit (a) Balance Outstanding Letters of Credit (a) Revolving Credit Facility — 23,255 — 24,730 CP Program 332,525 — 234,040 — Total Notes payable $ 332,525 $ 23,255 $ 234,040 $ 24,730 _______________ (a) Letters of credit are off-balance sheet commitments that reduce the borrowing capacity available on our corporate Revolving Credit Facility.
Credit Facility and Short Term Debt Covenants	Our Revolving Credit Facility and term loans require compliance with the following financial covenant, which we were in compliance with at September 30, 2021: As of September 30, 2021 Covenant Requirement Consolidated Indebtedness to Capitalization Ratio 62.4% Less than 65%

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Earnings Per Share Reconciliation	A reconciliation of share amounts used to compute earnings per share in the accompanying Condensed Consolidated Statements of Income was as follows (in thousands, except per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net income available for common stock $ 44,112 $ 36,283 $ 165,589 $ 150,423 Weighted average shares - basic 63,341 62,575 62,950 62,310 Dilutive effect of: Equity compensation 95 55 96 52 Weighted average shares - diluted 63,436 62,630 63,046 62,362 Earnings per share of common stock: Earnings per share, Basic $ 0.70 $ 0.58 $ 2.63 $ 2.41 Earnings per share, Diluted $ 0.70 $ 0.58 $ 2.63 $ 2.41
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following securities were excluded from the diluted earnings per share computation because of their anti-dilutive nature (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Equity compensation 9 22 12 22 Restricted stock — 49 1 40 Anti-dilutive shares 9 71 13 62

Risk Management and Derivativ_2

Risk Management and Derivatives (Tables)	9 Months Ended
	Sep. 30, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Contract or notional amounts and terms of marketing activities and derivative commodity instruments	We had the following net long positions as of: September 30, 2021 December 31, 2020 Units Notional Maximum Term (months) (a) Notional Maximum Term (months) (a) Natural gas futures purchased MMBtus 1,700,000 6 620,000 3 Natural gas options purchased, net MMBtus 8,420,000 6 3,160,000 3 Natural gas basis swaps purchased MMBtus 1,500,000 6 900,000 3 Natural gas over-the-counter swaps, net (b) MMBtus 5,920,000 35 3,850,000 17 Natural gas physical contracts, net (c) MMBtus 18,758,835 7 17,513,061 22 Electric wholesale contracts (c) MWh 65,625 3 219,000 12 __________ (a) Term reflects the maximum forward period hedged. (b) As of September 30, 2021, 2,700,000 MMBtus of natural gas over-the-counter swaps purchases were designated as cash flow hedges. (c)
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	The following table presents the fair value and balance sheet classification of our derivative instruments (in thousands) as of: Balance Sheet Location September 30, 2021 December 31, 2020 Derivatives designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 6,989 $ 181 Noncurrent commodity derivatives Other assets, non-current 32 43 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current — (108) Total derivatives designated as hedges $ 7,021 $ 116 Derivatives not designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 5,327 $ 1,667 Noncurrent commodity derivatives Other assets, non-current 1,580 151 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current (3,471) (1,936) Total derivatives not designated as hedges $ 3,436 $ (118)
Derivative Instruments, Gain (Loss)	The impacts of cash flow hedges on our Condensed Consolidated Statements of Comprehensive Income and Condensed Consolidated Statements of Income are presented below for the three and nine months ended September 30, 2021 and 2020. Note that this presentation does not reflect gains or losses arising from the underlying physical transactions; therefore, it is not indicative of the economic profit or loss we realized when the underlying physical and financial transactions were settled. Three Months Ended September 30, Three Months Ended September 30, 2021 2020 2021 2020 Derivatives in Cash Flow Hedging Relationships Amount of Gain/(Loss) Recognized in OCI Income Statement Location Amount of Gain/(Loss) Reclassified from AOCI into Income (in thousands) (in thousands) Interest rate swaps $ 712 $ 712 Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) $ (712) $ (712) Commodity derivatives 5,536 691 Fuel, purchased power and cost of natural gas sold 331 (178) Total $ 6,248 $ 1,403 $ (381) $ (890) Nine Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Derivatives in Cash Flow Hedging Relationships Amount of Gain/(Loss) Recognized in OCI Income Statement Location Amount of Gain/(Loss) Reclassified from AOCI into Income (in thousands) (in thousands) Interest rate swaps $ 2,138 $ 2,138 Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) $ (2,138) $ (2,138) Commodity derivatives 6,896 959 Fuel, purchased power and cost of natural gas sold 356 (734) Total $ 9,034 $ 3,097 $ (1,782) $ (2,872) The following table summarizes the impacts of derivative instruments not designated as hedge instruments on our Condensed Consolidated Statements of Income for the three and nine months ended September 30, 2021 and 2020. Note that this presentation does not reflect gains or losses arising from the underlying physical transactions; therefore, it is not indicative of the economic profit or loss we realized when the underlying physical and financial transactions were settled. Three Months Ended September 30, 2021 2020 Derivatives Not Designated as Hedging Instruments Location of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income (in thousands) Commodity derivatives - Electric Fuel, purchased power and cost of natural gas sold $ 2,494 $ (1,386) Commodity derivatives - Natural Gas Fuel, purchased power and cost of natural gas sold 4,004 1,777 $ 6,498 $ 391 Nine Months Ended September 30, 2021 2020 Derivatives Not Designated as Hedging Instruments Location of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income (in thousands) Commodity derivatives - Electric Fuel, purchased power and cost of natural gas sold $ (2,628) $ (228) Commodity derivatives - Natural Gas Fuel, purchased power and cost of natural gas sold 6,186 2,992 $ 3,558 $ 2,764

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value Hierarchy, Measured on Recurring Basis	The commodity contracts for our Utilities segments are valued using the market approach and include forward strip pricing at liquid delivery points, exchange-traded futures, options, basis swaps and over-the-counter swaps and options (Level 2) for wholesale electric energy and natural gas contracts. For exchange-traded futures, options and basis swap assets and liabilities, fair value was derived using broker quotes validated by the exchange settlement pricing for the applicable contract. For over-the-counter instruments, the fair value is obtained by utilizing a nationally recognized service that obtains observable inputs to compute the fair value, which we validate by comparing our valuation with the counterparty. The fair value of these swaps includes a CVA based on the credit spreads of the counterparties when we are in an unrealized gain position or on our own credit spread when we are in an unrealized loss position. For additional information, see Note 1 of our Notes to the Consolidated Financial Statements in our 2020 Annual Report on Form 10-K. As of September 30, 2021 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting (a) Total (in thousands) Assets: Commodity derivatives — Gas Utilities $ — $ 32,298 $ — $ (18,370) $ 13,928 Commodity derivatives — Electric Utilities $ — $ — $ — $ — $ — Total $ — $ 32,298 $ — $ (18,370) $ 13,928 Liabilities: Commodity derivatives — Gas Utilities $ — $ 1,128 $ — $ (141) $ 987 Commodity derivatives — Electric Utilities $ — $ 2,484 $ — $ — $ 2,484 Total $ — $ 3,612 $ — $ (141) $ 3,471 __________ (a) As of September 30, 2021, $18 million of our commodity derivative assets and $0.1 million of our commodity derivative liabilities, as well as related collateral amounts, were subject to master netting agreements. Collateral amounts are included in Other current assets on the Condensed Consolidated Balance Sheets. As of December 31, 2020 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting (a) Total (in thousands) Assets: Commodity derivatives — Gas Utilities $ — $ 2,504 $ — $ (1,527) $ 977 Commodity derivatives — Electric Utilities $ — $ 1,065 $ — $ — $ 1,065 Total $ — $ 3,569 $ — $ (1,527) $ 2,042 Liabilities: Commodity derivatives — Gas Utilities $ — $ 2,675 $ — $ (1,552) $ 1,123 Commodity derivatives — Electric Utilities $ — $ 921 $ — $ — $ 921 Total $ — $ 3,596 $ — $ (1,552) $ 2,044 __________ (a) As of December 31, 2020, $1.5 million of our commodity derivative assets and $1.6 million of our commodity derivative liabilities, as well as related collateral amounts, were subject to master netting agreements. Collateral amounts are included in Other current assets on the Condensed Consolidated Balance Sheets.
Fair Value, by Balance Sheet Grouping	The following table presents the carrying amounts and fair values of financial instruments not recorded at fair value on the Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2021 December 31, 2020 Carrying Fair Value Carrying Fair Value Long-term debt, including current maturities (a) $ 4,125,571 $ 4,614,244 $ 3,536,536 $ 4,208,167 __________ (a) Long-term debt is valued based on observable inputs available either directly or indirectly for similar liabilities in active markets and therefore is classified as Level 2 in the fair value hierarchy. Carrying amount of long-term debt is net of deferred financing costs.

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2021
Statement of Comprehensive Income [Abstract]
Reclassification Out of Accumulated Other Comprehensive Income (Loss)	The following table details reclassifications out of AOCI and into Net income. The amounts in parentheses below indicate decreases to Net income in the Condensed Consolidated Statements of Income for the period (in thousands): Location on the Condensed Consolidated Statements of Income Amount Reclassified from AOCI Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Gains and (losses) on cash flow hedges: Interest rate swaps Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) $ (712) $ (712) $ (2,138) $ (2,138) Commodity contracts Fuel, purchased power and cost of natural gas sold 331 (178) 356 (734) (381) (890) (1,782) (2,872) Income tax Income tax (expense) (26) 209 308 680 Total reclassification adjustments related to cash flow hedges, net of tax $ (407) $ (681) $ (1,474) $ (2,192) Amortization of components of defined benefit plans: Prior service cost Operations and maintenance $ 25 $ 24 $ 74 $ 79 Actuarial gain (loss) Operations and maintenance (598) (597) (1,793) (1,791) (573) (573) (1,719) (1,712) Income tax Income tax (expense) 133 143 492 407 Total reclassification adjustments related to defined benefit plans, net of tax $ (440) $ (430) $ (1,227) $ (1,305) Total reclassifications $ (847) $ (1,111) $ (2,701) $ (3,497)
Schedule of Accumulated Other Comprehensive Income (Loss)	Balances by classification included within AOCI, net of tax on the accompanying Condensed Consolidated Balance Sheets were as follows (in thousands): Derivatives Designated as Cash Flow Hedges Interest Rate Swaps Commodity Derivatives Employee Benefit Plans Total As of December 31, 2020 $ (12,558) $ 2 $ (14,790) $ (27,346) Other comprehensive income (loss) before reclassifications — 5,476 — 5,476 Amounts reclassified from AOCI 1,743 (269) 1,227 2,701 As of September 30, 2021 $ (10,815) $ 5,209 $ (13,563) $ (19,169) Derivatives Designated as Cash Flow Hedges Interest Rate Swaps Commodity Derivatives Employee Benefit Plans Total As of December 31, 2019 $ (15,122) $ (456) $ (15,077) $ (30,655) Other comprehensive income (loss) before reclassifications — 181 55 236 Amounts reclassified from AOCI 1,630 562 1,305 3,497 As of September 30, 2020 $ (13,492) $ 287 $ (13,717) $ (26,922)

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Schedule of Net Benefit Costs	The components of net periodic benefit cost for the Defined Benefit Pension Plan were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Service cost $ 1,260 $ 1,352 $ 3,779 $ 4,058 Interest cost 2,328 3,356 6,984 10,069 Expected return on plan assets (5,219) (5,647) (15,657) (16,943) Net loss 1,828 2,093 5,486 6,279 Net periodic benefit cost $ 197 $ 1,154 $ 592 $ 3,463 Defined Benefit Postretirement Healthcare Plan The components of net periodic benefit cost for the Defined Benefit Postretirement Healthcare Plan were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Service cost $ 560 $ 514 $ 1,678 $ 1,542 Interest cost 264 412 793 1,237 Expected return on plan assets (34) (46) (102) (137) Prior service cost (benefit) (108) (136) (326) (410) Net loss 116 5 350 15 Net periodic benefit cost $ 798 $ 749 $ 2,393 $ 2,247 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans The components of net periodic benefit cost for the Supplemental Non-qualified Defined Benefit and Defined Contribution Plans were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Service cost $ 235 $ 1,035 $ 1,948 $ 1,482 Interest cost 176 274 530 824 Prior service cost — 1 — 1 Net loss 439 425 1,316 1,277 Net periodic benefit cost $ 850 $ 1,735 $ 3,794 $ 3,584
Schedule of Defined Benefit Plans Contributions	Contributions made in the first nine months of 2021 and anticipated contributions for 2021 and 2022 are as follows (in thousands): Contributions Made Additional Contributions Contributions Nine Months Ended September 30, 2021 Anticipated for 2021 Anticipated for 2022 Defined Benefit Pension Plan $ — $ — $ 3,900 Non-pension Defined Benefit Postretirement Healthcare Plan $ 4,145 $ 1,382 $ 5,202 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans $ 1,445 $ 482 $ 2,149

Business Segment Information (T

Business Segment Information (Tables)	9 Months Ended
	Sep. 30, 2021
Segment Reporting Information, Additional Information [Abstract]
Schedule of Segment Reporting Information, by Segment	Segment information was as follows (in thousands): Total assets (net of intercompany eliminations) as of: September 30, 2021 December 31, 2020 Electric Utilities $ 3,267,074 $ 3,120,928 Gas Utilities 5,052,898 4,376,204 Power Generation 398,915 404,220 Mining 76,791 77,085 Corporate and Other 114,712 110,349 Total assets $ 8,910,390 $ 8,088,786 Three Months Ended September 30, 2021 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 207,374 $ 203 $ 5,526 $ — $ 213,103 Gas Utilities 161,977 1,087 1,520 99 164,683 Power Generation 2,333 412 23,725 50 26,520 Mining 6,969 235 8,845 339 16,388 Inter-company eliminations — — (39,616) (488) (40,104) Total $ 378,653 $ 1,937 $ — $ — $ 380,590 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 Nine Months Ended September 30, 2021 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 604,966 $ 2,619 $ 17,859 $ — $ 625,444 Gas Utilities 743,663 4,745 4,559 285 753,252 Power Generation 8,006 1,219 71,656 150 81,031 Mining 20,658 718 23,093 1,020 45,489 Inter-company eliminations — — (117,167) (1,455) (118,622) Total $ 1,377,293 $ 9,301 $ — $ — $ 1,386,594 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 Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Adjusted operating income: Electric Utilities $ 57,608 $ 52,083 $ 114,989 $ 121,726 Gas Utilities 17,257 18,147 139,336 139,253 Power Generation 10,323 8,738 32,842 31,489 Mining 4,908 3,505 11,813 9,992 Corporate and Other (223) (239) (3,526) (108) Operating income 89,873 82,234 295,454 302,352 Interest expense, net (38,018) (36,041) (113,820) (107,039) Impairment of investment — — — (6,859) Other income (expense), net 1,560 (1,193) 1,635 (703) Income tax (expense) (5,253) (4,651) (6,333) (25,484) Net income 48,162 40,349 176,936 162,267 Net income attributable to non-controlling interest (4,050) (4,066) (11,347) (11,844) Net income available for common stock $ 44,112 $ 36,283 $ 165,589 $ 150,423

Selected Balance Sheet Inform_2

Selected Balance Sheet Information (Tables)	9 Months Ended
	Sep. 30, 2021
Selected Balance Sheet Information [Abstract]
Account Receivable Schedule	Following is a summary of Accounts receivable, net included in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2021 December 31, 2020 Accounts receivable, trade $ 120,930 $ 146,899 Unbilled revenue 63,338 126,065 Less: Allowance for credit losses (2,312) (7,003) Accounts receivable, net $ 181,956 $ 265,961
Financing Receivable, Current, Allowance for Credit Loss	Changes to allowance for credit losses for the nine months ended September 30, 2021 and 2020, respectively, were as follows (in thousands): Balance at Beginning of Year Additions Charged to Costs and Expenses Recoveries and Other Additions Write-offs and Other Deductions Balance at September 30, 2021 $ 7,003 $ 1,111 $ 2,420 $ (8,222) $ 2,312 2020 $ 2,444 $ 8,471 $ 3,720 $ (6,026) $ 8,609
Materials, Supplies, and Fuel Schedule	The following amounts by major classification are included in Materials, supplies and fuel on the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2021 December 31, 2020 Materials and supplies $ 85,612 $ 85,250 Fuel - Electric Utilities 1,240 1,531 Natural gas in storage 58,891 30,619 Total materials, supplies and fuel $ 145,743 $ 117,400
Accrued Liabilities Schedule	The following amounts by major classification are included in Accrued liabilities on the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2021 December 31, 2020 Accrued employee compensation, benefits and withholdings $ 72,328 $ 77,806 Accrued property taxes 44,231 47,105 Customer deposits and prepayments 53,652 52,185 Accrued interest 46,532 31,520 Other (none of which is individually significant) 33,092 34,996 Total accrued liabilities $ 249,835 $ 243,612

Regulatory Matters (Details)

Regulatory Matters (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Regulatory assets
Regulatory assets	$ 830,055	$ 278,258
Less current regulatory assets	(213,031)	(51,676)
Regulatory assets, non-current	617,024	226,582
Regulatory liabilities
Regulatory liabilities	526,417	532,720
Less current regulatory liabilities	(30,156)	(25,061)
Regulatory liabilities, non-current	496,261	507,659
Deferred energy and gas costs
Regulatory liabilities
Regulatory liabilities	9,408	13,253
Gas price derivatives
Regulatory liabilities
Regulatory liabilities	13,234	0
Employee benefit plans and related deferred taxes
Regulatory liabilities
Regulatory liabilities	39,203	40,256
Cost of removal
Regulatory liabilities
Regulatory liabilities	181,180	172,902
Excess deferred income taxes
Regulatory liabilities
Regulatory liabilities	266,477	285,259
Other regulatory liabilities
Regulatory liabilities
Regulatory liabilities	16,915	21,050
Winter Storm Uri Incremental Costs in a Separately Tracked Mechanism
Regulatory assets
Regulatory assets	532,766	0
Deferred energy and gas costs
Regulatory assets
Regulatory assets	59,741	39,035
Deferred gas cost adjustments
Regulatory assets
Regulatory assets	6,076	3,200
Gas price derivatives
Regulatory assets
Regulatory assets	0	2,226
Deferred taxes on AFUDC
Regulatory assets
Regulatory assets	7,537	7,491
Employee benefit plans and related deferred taxes
Regulatory assets
Regulatory assets	114,234	116,598
Environmental
Regulatory assets
Regulatory assets	1,395	1,413
Loss on reacquired debt
Regulatory assets
Regulatory assets	21,460	22,864
Deferred taxes on flow through accounting
Regulatory assets
Regulatory assets	54,199	47,515
Decommissioning costs
Regulatory assets
Regulatory assets	6,583	8,988
Gas supply contract termination
Regulatory assets
Regulatory assets	0	2,524
Other regulatory assets
Regulatory assets
Regulatory assets	$ 26,064	$ 26,404

Regulatory Matters_ Winter Stor

Regulatory Matters: Winter Storm Uri (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory assets	$ 830,055	$ 278,258
Winter Storm Uri Incremental Costs in a Separately Tracked Mechanism
Public Utilities, General Disclosures [Line Items]
Regulatory assets	532,766	0
Deferred gas cost adjustments
Public Utilities, General Disclosures [Line Items]
Regulatory assets	6,076	$ 3,200
Winter Storm Uri
Public Utilities, General Disclosures [Line Items]
Amount Recovered Through Regulatory Mechanism	15,000
Winter Storm Uri | Winter Storm Uri Incremental Costs in a Separately Tracked Mechanism
Public Utilities, General Disclosures [Line Items]
Regulatory assets	$ 546,000
Regulatory Asset, Amortization Period	3 years 8 months 12 days
Winter Storm Uri | Carrrying Costs
Public Utilities, General Disclosures [Line Items]
Regulatory assets	$ 1,800
Winter Storm Uri | Deferred gas cost adjustments
Public Utilities, General Disclosures [Line Items]
Regulatory assets	$ 13,000

Regulatory Matters_ Tax Cut and

Regulatory Matters: Tax Cut and Jobs Act (Details) - USD ($) $ in Thousands	Jan. 01, 2022	Apr. 30, 2021	Jan. 26, 2021	Dec. 30, 2020
Colorado Public Utilities Commission (CPUC) | Colorado Electric
Public Utilities, General Disclosures [Line Items]
Settlement of plan to provide TCJA-related customer billing credits to its customers				$ 9,300
Annual TCJA-Related Customer Billing Credits		$ 900
Nebraska Public Service Commission (NPSC) | Nebraska Gas
Public Utilities, General Disclosures [Line Items]
Settlement of plan to provide TCJA-related customer billing credits to its customers			$ 2,900
Kansas Corporation Commission (KCC) | Kansas Gas | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Settlement of Plan to Provide TCJA and State Tax Reform benefits to Customers Annually	$ 3,000
Number of Years TCJA and State Tax Reform Benefits to be Provide to Customers	3 years
Settlement Total of Plan to Provide TCJA and State Tax Reform benefits to Customers	$ 9,100

Regulatory Matters_ Rate Review

Regulatory Matters: Rate Review (Details) $ in Millions	Oct. 08, 2021USD ($)mi	Oct. 05, 2021USD ($)mi	Jul. 06, 2021	Jun. 01, 2021USD ($)mi	Mar. 01, 2021USD ($)mi	Sep. 11, 2020
Settlement agreement reached with CPUC Staff and various intervenors, subject to the review and approval by an Administrative Law Judge and the CPUC. | Colorado Public Utilities Commission (CPUC) | Colorado Gas | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Public Utilities - Length of Natural Gas Pipeline to Receive Infrastructure Investments | mi		7,000
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 6.5
Public Utilities, Approved Equity Capital Structure, Percentage		50.30%
Public Utilities, Approved Debt Capital Structure, Percentage		49.70%
Public Utilities, Requested Return on Equity, Percentage		9.20%
Rate Review Filed with the Regulatory Agency | Colorado Public Utilities Commission (CPUC) | Colorado Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Term Extension of System Safety and Integrity Rider						5 years
Rate Review Filed with the Regulatory Agency | Iowa Utilities Board (IUB) | Iowa Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities - Length of Natural Gas Pipeline to Receive Infrastructure Investments | mi				5,000
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 8.3
Public Utilities, Requested Equity Capital Structure, Percentage				50.00%
Public Utilities, Requested Debt Capital Structure, Percentage				50.00%
Public Utilities, Requested Return on Equity, Percentage				10.15%
Public Utilities Amount of System Safety and Integrity Rider Moved to Base Rates Requested				$ 2.2
Public Utilities, Number of Days After Filing a Rate Review the Interim Rates May Be Implemented				10 days
Rate Review Approved by Regulatory Agency | Colorado Public Utilities Commission (CPUC) | Colorado Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Term Extension of System Safety and Integrity Rider			3 years
Rate Review Approved by Regulatory Agency | Nebraska Publc Service Commission (NPSC) | Nebraska Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage					9.50%
Public Utilities, Approved Equity Capital Structure, Percentage					50.00%
Public Utilities, Approved Debt Capital Structure, Percentage					50.00%
Public Utilities Amount of System Safety and Integrity Rider Moved to Base Rates Requested					$ 4.6
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 6.5
Global Settlement agreement with KCC Staff and various intervenors for a general rate increase and renewal of its safety and integrity rider. | Kansas Corporation Commission (KCC) | Kansas Gas | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Public Utilities - Length of Natural Gas Pipeline to Receive Infrastructure Investments | mi	4,600
Public Utilities, Term Extension of System Safety and Integrity Rider	5 years
Public Utilities Amount of System Safety and Integrity Rider Moved to Base Rates Requested	$ 6.6
Approval Recevied from Regulatory Agency | Nebraska Publc Service Commission (NPSC) | Nebraska Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities - Length of Natural Gas Pipeline to Receive Infrastructure Investments | mi					13,000
Public Utilities, Term Extension of System Safety and Integrity Rider					5 years

Commitments, Contingencies an_2

Commitments, Contingencies and Guarantees (Details) - Colorado Electric - TC Colorado Solar, LLC - Solar	Feb. 19, 2021MW
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of Megawatts Capacity Purchased	200
Purchase Power Agreement Set to Expire after a Certain Number of Years Following Completion of the Facility	15 years

Revenue_ Disaggregation of Reve

Revenue: Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 378,653	$ 344,312	$ 1,377,293	$ 1,198,714
Total revenues	380,590	346,590	1,386,594	1,210,554
Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,968	6,568	20,658	20,062
Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	371,685	337,744	1,356,635	1,178,652
Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	1,937	2,278	9,301	11,840
Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	302,858	270,440	1,158,968	993,219
Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	37,541	38,057	116,922	112,680
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,189	7,453	20,794	19,572
Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13,586	7,667	25,784	12,014
Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18,479	20,695	54,825	61,229
Inter-company Revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(39,616)	(39,899)	(117,167)	(117,083)
Total revenues	(40,104)	(39,935)	(118,622)	(117,902)
Inter-company Revenues | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(8,846)	(8,100)	(23,093)	(23,855)
Inter-company Revenues | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(30,770)	(31,799)	(94,074)	(93,228)
Inter-company Revenues | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(488)	(36)	(1,455)	(819)
Inter-company Revenues | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(8,846)	(8,100)	(23,093)	(23,855)
Inter-company Revenues | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(110)	(139)	(329)	(416)
Inter-company Revenues | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(23,725)	(24,521)	(71,656)	(72,609)
Inter-company Revenues | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1,638)	(1,904)	(6,197)	(6,123)
Inter-company Revenues | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(5,297)	(5,235)	(15,892)	(14,080)
Electric Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	212,900	200,618	622,825	536,107
Total revenues	213,103	200,842	625,444	538,181
Electric Utilities | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Electric Utilities | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	212,900	200,618	622,825	536,107
Electric Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	203	224	2,619	2,074
Electric Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	179,982	169,505	536,952	459,949
Electric Utilities | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Electric Utilities | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,856	5,925	12,788	14,947
Electric Utilities | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,149	9,535	31,746	17,940
Electric Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13,913	15,653	41,339	43,271
Gas Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	163,497	142,876	748,222	658,539
Total revenues	164,683	143,929	753,252	665,812
Gas Utilities | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Gas Utilities | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	163,497	142,876	748,222	658,539
Gas Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	1,186	1,053	5,030	7,273
Gas Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	115,908	94,367	601,358	513,208
Gas Utilities | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	37,651	38,196	117,251	113,096
Gas Utilities | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Gas Utilities | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	75	36	235	197
Gas Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9,863	10,277	29,378	32,038
Power Generation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26,058	26,049	79,662	77,234
Total revenues	26,520	26,518	81,031	78,606
Power Generation | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Power Generation | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26,058	26,049	79,662	77,234
Power Generation | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	462	469	1,369	1,372
Power Generation | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Power Generation | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Power Generation | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26,058	26,049	79,662	77,234
Power Generation | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Power Generation | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Mining
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,814	14,668	43,751	43,917
Total revenues	16,388	15,236	45,489	45,857
Mining | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,814	14,668	43,751	43,917
Mining | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Mining | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	574	568	1,738	1,940
Mining | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,814	14,668	43,751	43,917
Mining | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Mining | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Mining | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Mining | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0	$ 0	$ 0

Financing_ Schedule of Short-te

Financing: Schedule of Short-term Debt and Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Short-term Debt [Line Items]
Notes payable	$ 332,525	$ 234,040
Letters of Credit	23,255	24,730
Commercial Paper
Short-term Debt [Line Items]
Notes payable	332,525	234,040
Letters of Credit	0	0
Revolving Credit Facility
Short-term Debt [Line Items]
Notes payable	0	0
Letters of Credit	$ 23,255	$ 24,730

Financing_ Revolving Credit Fac

Financing: Revolving Credit Facility and CP Program (Details) $ in Thousands	Jul. 19, 2021USD ($)credit_extension	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)
Line of Credit Facility, Maximum Borrowing Capacity	$ 750,000
Net borrowings (payments) of Revolving Credit Facility and CP Program		$ 98,485	$ (265,180)
Commercial Paper
Short-term interest rate		0.19%
Revolving Credit Facility
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,000,000
Number Of One Year Extension Options | credit_extension	2
Debt Instrument, Term	1 year
Line of Credit Facility, Commitment Fee Percentage	0.175%
Revolving Credit Facility | Base Rate
Line of Credit Facility, Interest Rate at Period End	0.125%
Revolving Credit Facility | Eurodollar
Line of Credit Facility, Interest Rate at Period End	1.125%
Revolving Credit Facility | Letter of Credit
Line of Credit Facility, Interest Rate at Period End	1.125%

Financing_ Term Loan (Details)

Financing: Term Loan (Details) - USD ($) $ in Thousands	Feb. 24, 2021	Mar. 31, 2021	Sep. 30, 2021	Sep. 30, 2020
Repayments of Other Short-term Debt			$ 800,000	$ 0
Senior Unsecured Notes Due 2021 | Line of Credit
Debt Instrument, Term	9 months
Debt Instrument, Face Amount	$ 800,000
Payment for Debt Extinguishment or Debt Prepayment Cost			$ 0
Repayments of Other Short-term Debt		$ 200,000

Financing_ Long-term debt (Deta

Financing: Long-term debt (Details) - Senior Unsecured Notes Due 2024 $ in Millions	Aug. 26, 2021USD ($)
Debt Instrument, Face Amount	$ 600
Debt Instrument, Interest Rate, Stated Percentage	1.037%
Debt Instrument, Term	3 years
Debt Issuance Costs, Net	$ 3.7

Financing_ Debt Covenants (Deta

Financing: Debt Covenants (Details)	Sep. 30, 2021
Line of Credit Facility [Line Items]
Ratio of Indebtedness to Net Capital	0.624
Maximum
Line of Credit Facility [Line Items]
Consolidated Indebtedness to Capitalization Ratio	0.65

Financing_ Equity (Details)

Financing: Equity (Details) - Common Stock - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
At The Market Equity Offering Program Shares Issued	300,000	900,000
At The Market Equity Program Proceeds from Sale of Stock	$ 23,000	$ 63,000
At The Market Equity Program Stock Issued Issuance Costs	$ 200	$ 600

Earnings Per Share_ Earnings Pe

Earnings Per Share: Earnings Per Share Reconciliation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income available for common stock	$ 44,112	$ 36,283	$ 165,589	$ 150,423
Weighted average shares - basic (in shares)	63,341	62,575	62,950	62,310
Dilutive effect of:
Equity compensation (in shares)	95	55	96	52
Weighted average shares - diluted (in shares)	63,436	62,630	63,046	62,362
Earnings per share, Basic (usd per share)	$ 0.70	$ 0.58	$ 2.63	$ 2.41
Earnings per share, Diluted (usd per share)	$ 0.70	$ 0.58	$ 2.63	$ 2.41

Earnings Per Share_ Anti-diluti

Earnings Per Share: Anti-dilutive shares (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	9	71	13	62
Equity compensation - (in shares)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	9	22	12	22
Restricted Stock (in shares)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	0	49	1	40

Risk Management and Derivativ_3

Risk Management and Derivatives: Utilities (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021USD ($)mWMMBTU	Dec. 31, 2020MMBTUmW
Commodity Contract
Derivative [Line Items]
Credit Risk Derivative Liabilities, at Fair Value | $	$ 0.9
Natural Gas, Distribution | Cash Flow Hedging
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	2,700,000
Natural Gas, Distribution | Natural gas futures purchased
Derivative [Line Items]
Derivative, Remaining Maturity	6 months	3 months
Natural Gas, Distribution | Natural gas futures purchased | Long
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	1,700,000	620,000
Natural Gas, Distribution | Natural gas options purchased, net
Derivative [Line Items]
Derivative, Remaining Maturity	6 months	3 months
Natural Gas, Distribution | Natural gas options purchased, net | Long
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	8,420,000	3,160,000
Natural Gas, Distribution | Natural gas basis swaps purchased
Derivative [Line Items]
Derivative, Remaining Maturity	6 months	3 months
Natural Gas, Distribution | Natural gas basis swaps purchased | Long
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	1,500,000	900,000
Natural Gas, Distribution | Natural gas over-the-counter swaps, net
Derivative [Line Items]
Derivative, Remaining Maturity	35 months	17 months
Natural Gas, Distribution | Natural gas over-the-counter swaps, net | Long
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	5,920,000	3,850,000
Natural Gas, Distribution | Natural gas physical contracts, net
Derivative [Line Items]
Derivative, Remaining Maturity	7 months	22 months
Natural Gas, Distribution | Natural gas physical contracts, net | Long
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	18,758,835	17,513,061
Electricity | Electric wholesale contracts
Derivative [Line Items]
Derivative, Remaining Maturity	3 months	12 months
Electricity | Electric wholesale contracts | Long
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | mW	65,625	219,000

Risk Management and Derivativ_4

Risk Management and Derivatives: Derivatives by Balance Sheet Classification (Details) - Commodity Contract - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair Value Hedges, Net	$ 7,021	$ 116
Designated as Hedging Instrument | Derivative assets — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	6,989	181
Designated as Hedging Instrument | Other assets, non-current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	32	43
Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	0	(108)
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair Value Hedges, Net	3,436	(118)
Not Designated as Hedging Instrument | Derivative assets — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	5,327	1,667
Not Designated as Hedging Instrument | Other assets, non-current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	1,580	151
Not Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	$ (3,471)	$ (1,936)

Risk Management and Derivativ_5

Risk Management and Derivatives: Derivatives Designated as Hedge Instruments (Details) - Cash Flow Hedging - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (381)	$ (890)	$ (1,782)	$ (2,872)
Designated as Hedging Instrument
Derivative [Line Items]
Unrealized Gain (Loss) on Price Risk Cash Flow Derivatives, before Tax	6,248	1,403	9,034	3,097
Interest rate swaps | Interest Expense
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(712)	(712)	(2,138)	(2,138)
Interest rate swaps | Designated as Hedging Instrument
Derivative [Line Items]
Unrealized Gain (Loss) on Price Risk Cash Flow Derivatives, before Tax	712	712	2,138	2,138
Commodity Contract | Fuel, purchased power and cost of natural gas sold
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	331	(178)	356	(734)
Commodity Contract | Designated as Hedging Instrument
Derivative [Line Items]
Unrealized Gain (Loss) on Price Risk Cash Flow Derivatives, before Tax	$ 5,536	$ 691	6,896	$ 959
Interest Rate Swap and Commodity Derivative
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			$ 4,000

Risk Management and Derivativ_6

Risk Management and Derivatives: Derivatives Not Designated as Hedge Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Derivative [Line Items]
Regulatory Liabilities	$ 526,417		$ 526,417		$ 532,720
Regulatory assets	(830,055)		(830,055)		(278,258)
Gas price derivatives
Derivative [Line Items]
Regulatory Liabilities	13,234		13,234		0
Gas price derivatives
Derivative [Line Items]
Regulatory assets	0		0		$ (2,226)
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	6,498	$ 391	3,558	$ 2,764
Not Designated as Hedging Instrument | Fuel, purchased power and cost of natural gas sold | Electricity
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	2,494	(1,386)	(2,628)	(228)
Not Designated as Hedging Instrument | Fuel, purchased power and cost of natural gas sold | Natural Gas, Distribution
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 4,004	$ 1,777	$ 6,186	$ 2,992

Fair Value Measurements_ Schedu

Fair Value Measurements: Schedule of Fair Values (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
ContractSubjecttoMasterNetting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 18,000	$ 1,500
Derivative Liability, Fair Value, Gross Liability	100	1,600
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(18,370)	(1,527)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(141)	(1,552)
Fair Value, Measurements, Recurring | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	13,928	2,042
Derivative Liabilities, Total	3,471	2,044
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	0	0
Derivative Liabilities, Total	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	32,298	3,569
Derivative Liabilities, Total	3,612	3,596
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	0	0
Derivative Liabilities, Total	0	0
Fair Value, Measurements, Recurring | Gas Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(18,370)	(1,527)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(141)	(1,552)
Fair Value, Measurements, Recurring | Gas Utilities | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	13,928	977
Derivative Liabilities, Fair Value Disclosure	987	1,123
Fair Value, Measurements, Recurring | Gas Utilities | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	0	0
Derivative Liabilities, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring | Gas Utilities | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	32,298	2,504
Derivative Liabilities, Fair Value Disclosure	1,128	2,675
Fair Value, Measurements, Recurring | Gas Utilities | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	0	0
Derivative Liabilities, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring | Electric Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	0	0
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	0	0
Fair Value, Measurements, Recurring | Electric Utilities | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	0	1,065
Derivative Liabilities, Fair Value Disclosure	2,484	921
Fair Value, Measurements, Recurring | Electric Utilities | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	0	0
Derivative Liabilities, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring | Electric Utilities | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	0	1,065
Derivative Liabilities, Fair Value Disclosure	2,484	921
Fair Value, Measurements, Recurring | Electric Utilities | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	0	0
Derivative Liabilities, Fair Value Disclosure	$ 0	$ 0

Fair Value Measurements_ Other

Fair Value Measurements: Other Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 4,125,571	$ 3,536,536
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 4,614,244	$ 4,208,167

Other Comprehensive Income_ Rec

Other Comprehensive Income: Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Condensed Statement of Income Captions [Line Items]
Interest Expense	$ 38,604			$ 36,521			$ 115,098	$ 108,067
Fuel, purchased power and cost of natural gas sold	94,057			71,686			495,678	331,194
Operations and maintenance	122,277			122,759			375,201	365,533
Income tax benefit (expense)	(5,253)			(4,651)			(6,333)	(25,484)
Net income (loss)	48,162	$ 28,287	$ 100,487	40,349	$ 24,694	$ 97,224	176,936	162,267
Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Net income (loss)	(847)			(1,111)			(2,701)	(3,497)
Reclassification out of Accumulated Other Comprehensive Income | Cash Flow Hedging
Condensed Statement of Income Captions [Line Items]
Income before Income Taxes	(381)			(890)			(1,782)	(2,872)
Income tax benefit (expense)	(26)			209			308	680
Net income (loss)	(407)			(681)			(1,474)	(2,192)
Reclassification out of Accumulated Other Comprehensive Income | Cash Flow Hedging | Interest rate swaps
Condensed Statement of Income Captions [Line Items]
Interest Expense	(712)			(712)			(2,138)	(2,138)
Reclassification out of Accumulated Other Comprehensive Income | Cash Flow Hedging | Commodity Contract
Condensed Statement of Income Captions [Line Items]
Fuel, purchased power and cost of natural gas sold	331			(178)			356	(734)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost
Condensed Statement of Income Captions [Line Items]
Operations and maintenance	25			24			74	79
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss)
Condensed Statement of Income Captions [Line Items]
Operations and maintenance	(598)			(597)			(1,793)	(1,791)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment
Condensed Statement of Income Captions [Line Items]
Income before Income Taxes	(573)			(573)			(1,719)	(1,712)
Income tax benefit (expense)	133			143			492	407
Net income (loss)	$ (440)			$ (430)			$ (1,227)	$ (1,305)

Other Comprehensive Income_ Acc

Other Comprehensive Income: Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	$ (27,346)	$ (30,655)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(19,169)	(26,922)
Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	(14,790)	(15,077)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	55
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(13,563)	(13,717)
Accumulated Defined Benefit Plans Adjustment | Reclassification out of Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1,227	1,305
Accumulated Other Comprehensive Income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	5,476	236
Accumulated Other Comprehensive Income (loss) | Reclassification out of Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	2,701	3,497
Interest Rate Swaps | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	(12,558)	(15,122)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(10,815)	(13,492)
Interest Rate Swaps | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent | Reclassification out of Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1,743	1,630
Commodity Contract | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	2	(456)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	5,476	181
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	5,209	287
Commodity Contract | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent | Reclassification out of Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ (269)	$ 562

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 1,260	$ 1,352	$ 3,779	$ 4,058
Interest cost	2,328	3,356	6,984	10,069
Expected return on plan assets	(5,219)	(5,647)	(15,657)	(16,943)
Net loss (gain)	1,828	2,093	5,486	6,279
Net periodic benefit cost	197	1,154	592	3,463
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer			0
Estimated Future Employer Contributions in Current Fiscal Year	0		0
Estimated Future Employer Contributions in Next Fiscal Year	3,900		3,900
Other Postretirement Benefits Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	560	514	1,678	1,542
Interest cost	264	412	793	1,237
Expected return on plan assets	(34)	(46)	(102)	(137)
Prior service cost (benefit)	(108)	(136)	(326)	(410)
Net loss (gain)	116	5	350	15
Net periodic benefit cost	798	749	2,393	2,247
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer			4,145
Estimated Future Employer Contributions in Current Fiscal Year	1,382		1,382
Estimated Future Employer Contributions in Next Fiscal Year	5,202		5,202
Supplemental Non-qualified Defined Benefit and Defined Contribution Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	235	1,035	1,948	1,482
Interest cost	176	274	530	824
Prior service cost (benefit)	0	1	0	1
Net loss (gain)	439	425	1,316	1,277
Net periodic benefit cost	850	$ 1,735	3,794	$ 3,584
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer			1,445
Estimated Future Employer Contributions in Current Fiscal Year	482		482
Estimated Future Employer Contributions in Next Fiscal Year	$ 2,149		$ 2,149

Income Taxes_ Winter Storm Uri

Income Taxes: Winter Storm Uri (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Deferred income tax liabilities, net	$ 445,036	$ 408,624
Winter Storm Uri
Deferred income tax liabilities, net	$ 130,000

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income tax benefit (expense)	$ (5,253)	$ (4,651)	$ (6,333)	$ (25,484)
Effective Tax Rate			3.50%	13.60%
Effective Income Tax Reconciliation, Tax Benefit From Amortization Of Excess Deferred Income Taxes			$ 2,200
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount			1,900
Effective Income Tax Reconciliation, Tax Flow-through Benefit from Repairs and Indirect Costs			1,100
Wind Assets
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Amount			3,200
Colorado Electric and Nebraska Gas
Effective Income Tax Rate Reconciliation Tax Cuts And Jobs Act Of 2017 Amount, Tax Benefit from Bill Credit			$ 10,000

Business Segment Information_ S

Business Segment Information: Segment and Corporate Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 8,910,390	$ 8,088,786
Corporate
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	114,712	110,349
Electric Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	3,267,074	3,120,928
Gas Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	5,052,898	4,376,204
Power Generation
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	398,915	404,220
Mining
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 76,791	$ 77,085

Business Segment Information_ I

Business Segment Information: Information Relating to Segment Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information
Revenue from contracts with customers	$ 378,653			$ 344,312			$ 1,377,293	$ 1,198,714
Revenues	380,590			346,590			1,386,594	1,210,554
Operating income	89,873			82,234			295,454	302,352
Interest expense, net	(38,018)			(36,041)			(113,820)	(107,039)
Impairment of investment	0			0			0	(6,859)
Other income (expense), net	1,560			(1,193)			1,635	(703)
Income tax (expense)	(5,253)			(4,651)			(6,333)	(25,484)
Net income	48,162	$ 28,287	$ 100,487	40,349	$ 24,694	$ 97,224	176,936	162,267
Net income attributable to non-controlling interest	(4,050)			(4,066)			(11,347)	(11,844)
Net income available for common stock	44,112			36,283			165,589	150,423
Inter-company Revenues
Segment Reporting Information
Revenue from contracts with customers	(39,616)			(39,899)			(117,167)	(117,083)
Revenues	(40,104)			(39,935)			(118,622)	(117,902)
Consolidation, Eliminations
Segment Reporting Information
Revenue from contracts with customers	0			0			0	0
Corporate
Segment Reporting Information
Operating income	(223)			(239)			(3,526)	(108)
Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	212,900			200,618			622,825	536,107
Revenues	213,103			200,842			625,444	538,181
Operating income	57,608			52,083			114,989	121,726
Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	163,497			142,876			748,222	658,539
Revenues	164,683			143,929			753,252	665,812
Operating income	17,257			18,147			139,336	139,253
Power Generation
Segment Reporting Information
Revenue from contracts with customers	26,058			26,049			79,662	77,234
Revenues	26,520			26,518			81,031	78,606
Operating income	10,323			8,738			32,842	31,489
Mining
Segment Reporting Information
Revenue from contracts with customers	15,814			14,668			43,751	43,917
Revenues	16,388			15,236			45,489	45,857
Operating income	4,908			3,505			11,813	9,992
Other revenues
Segment Reporting Information
Revenues	1,937			2,278			9,301	11,840
Other revenues | Inter-company Revenues
Segment Reporting Information
Revenues	(488)			(36)			(1,455)	(819)
Other revenues | Consolidation, Eliminations
Segment Reporting Information
Revenues	0			0			0	0
Other revenues | Electric Utilities
Segment Reporting Information
Revenues	203			224			2,619	2,074
Other revenues | Gas Utilities
Segment Reporting Information
Revenues	1,186			1,053			5,030	7,273
Other revenues | Power Generation
Segment Reporting Information
Revenues	462			469			1,369	1,372
Other revenues | Mining
Segment Reporting Information
Revenues	574			568			1,738	1,940
External Customers
Segment Reporting Information
Revenue from contracts with customers	378,653			344,312			1,377,293	1,198,714
External Customers | Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	207,374			194,941			604,966	518,641
External Customers | Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	161,977			141,275			743,663	655,386
External Customers | Power Generation
Segment Reporting Information
Revenue from contracts with customers	2,333			1,528			8,006	4,625
External Customers | Mining
Segment Reporting Information
Revenue from contracts with customers	6,969			6,568			20,658	20,062
External Customers | Other revenues
Segment Reporting Information
Revenues	1,937			2,278			9,301	11,840
External Customers | Other revenues | Electric Utilities
Segment Reporting Information
Revenues	203			224			2,619	2,074
External Customers | Other revenues | Gas Utilities
Segment Reporting Information
Revenues	1,087			863			4,745	7,083
External Customers | Other revenues | Power Generation
Segment Reporting Information
Revenues	412			414			1,219	1,206
External Customers | Other revenues | Mining
Segment Reporting Information
Revenues	235			777			718	1,477
Intercompany Customers | Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	5,526			5,677			17,859	17,466
Intercompany Customers | Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	1,520			1,601			4,559	3,153
Intercompany Customers | Power Generation
Segment Reporting Information
Revenue from contracts with customers	23,725			24,521			71,656	72,609
Intercompany Customers | Mining
Segment Reporting Information
Revenue from contracts with customers	8,845			8,100			23,093	23,855
Intercompany Customers | Other revenues | Electric Utilities
Segment Reporting Information
Revenues	0			0			0	0
Intercompany Customers | Other revenues | Gas Utilities
Segment Reporting Information
Revenues	99			190			285	190
Intercompany Customers | Other revenues | Power Generation
Segment Reporting Information
Revenues	50			55			150	166
Intercompany Customers | Other revenues | Mining
Segment Reporting Information
Revenues	$ 339			$ (209)			$ 1,020	$ 463

Selected Balance Sheet Inform_3

Selected Balance Sheet Information: Accounts Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Selected Balance Sheet Information [Abstract]
Accounts receivable, trade	$ 120,930	$ 146,899
Unbilled revenue	63,338	126,065
Less: Allowance for doubtful accounts	(2,312)	(7,003)	$ (8,609)	$ (2,444)
Accounts receivable, net	$ 181,956	$ 265,961

Selected Balance Sheet Inform_4

Selected Balance Sheet Information: Changes to Allowance for Credit Losses (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Selected Balance Sheet Information [Abstract]
Balance at Beginning of Year	$ 7,003	$ 2,444
Additions Charged to Costs and Expenses	1,111	8,471
Recoveries and Other Additions	2,420	3,720
Write-offs and Other Deductions	(8,222)	(6,026)
Balance at End of Year	$ 2,312	$ 8,609

Selected Balance Sheet Inform_5

Selected Balance Sheet Information: Materials and Supplies (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Selected Balance Sheet Information [Abstract]
Materials and supplies	$ 85,612	$ 85,250
Fuel - Electric Utilities	1,240	1,531
Natural gas in storage	58,891	30,619
Total materials, supplies and fuel	$ 145,743	$ 117,400

Selected Balance Sheet Inform_6

Selected Balance Sheet Information: Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Selected Balance Sheet Information [Abstract]
Accrued employee compensation, benefits and withholdings	$ 72,328	$ 77,806
Accrued property taxes	44,231	47,105
Customer deposits and prepayments	53,652	52,185
Accrued interest	46,532	31,520
Other (none of which is individually significant)	33,092	34,996
Total accrued liabilities	$ 249,835	$ 243,612