Black Hills (BKH) 10-Q 5 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 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		62,871,727
Entity Central Index Key	0001130464
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
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
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Revenues	$ 633,432	$ 537,050
Operating expenses:
Fuel, purchased power and cost of natural gas sold	293,147	187,879
Operations and maintenance	129,679	125,466
Depreciation, depletion and amortization	57,269	56,402
Taxes - property and production	15,022	14,118
Total operating expenses	495,117	383,865
Operating income	138,315	153,185
Other income (expense):
Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts)	(37,825)	(35,781)
Interest income	225	328
Impairment of investment	0	(6,859)
Other income (expense), net	266	2,353
Total other income (expense)	(37,334)	(39,959)
Income before income taxes	100,981	113,226
Income tax (expense)	(494)	(16,002)
Net income	100,487	97,224
Net income attributable to noncontrolling interest	(4,171)	(4,050)
Net income available for common stock	$ 96,316	$ 93,174
Earnings per share of common stock:
Earnings per share, Basic (usd per share)	$ 1.54	$ 1.51
Earnings per share, Diluted (usd per share)	$ 1.54	$ 1.51
Weighted average common shares outstanding:
Basic (in shares)	62,633	61,778
Diluted (in shares)	62,691	61,856

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net income	$ 100,487	$ 97,224
Other comprehensive income (loss), net of tax:
Benefit plan liability adjustments - net gain (net of tax of $0 and $(17), respectively)	0	55
Reclassification adjustments of benefit plan liability - prior service cost (net of tax of $9 and $7, respectively)	(16)	(23)
Reclassification adjustments of benefit plan liability - net loss (net of tax of $(217) and $(95), respectively)	381	502
Other comprehensive income, net of tax	1,018	1,273
Comprehensive income	101,505	98,497
Net income attributable to noncontrolling interest	(4,171)	(4,050)
Comprehensive income available for common stock	97,334	94,447
Interest rate swaps
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses on settled/amortized derivatives, net of tax	523	543
Commodity Contract
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses on settled/amortized derivatives, net of tax	23	371
Net unrealized gains (losses) on commodity derivatives (net of tax of $(35) and $54, respectively)	$ 107	$ (175)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
(Tax) benefit on benefit plan liability adjustments - net gain (loss)	$ 0	$ (17)
(Tax) benefit on benefit plan liability adjustments - prior service costs	(9)	(7)
(Tax) benefit on reclassification adjustment of benefit plan liability - net loss	(217)	(95)
Interest rate swaps
Tax (benefit) on reclassification of net realized (gains) losses on settled/amortized derivatives	(190)	(170)
Commodity Contract
Tax (benefit) on reclassification of net realized (gains) losses on settled/amortized derivatives	(8)	(115)
(Tax) benefit on net unrealized gains (losses) on commodity derivatives	$ (35)	$ 54

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 13,442	$ 6,356
Restricted cash and equivalents	4,483	4,383
Accounts receivable, net	282,382	265,961
Materials, supplies and fuel	102,603	117,400
Derivative assets, current	1,917	1,848
Income tax receivable, net	18,115	19,446
Regulatory assets, current	129,951	51,676
Other current assets	25,722	26,221
Total current assets	578,615	493,291
Property, plant and equipment	7,415,818	7,305,530
Less: accumulated depreciation and depletion	(1,320,525)	(1,285,816)
Total property, plant and equipment, net	6,095,293	6,019,714
Other assets:
Goodwill	1,299,454	1,299,454
Intangible assets, net	11,649	11,944
Regulatory assets, non-current	672,306	226,582
Other assets, non-current	38,882	37,801
Total other assets, non-current	2,022,291	1,575,781
TOTAL ASSETS	8,696,199	8,088,786
Current liabilities:
Accounts payable	160,179	183,340
Accrued liabilities	230,444	243,612
Derivative liabilities, current	2,526	2,044
Regulatory liabilities, current	13,580	25,061
Notes payable	815,870	234,040
Current maturities of long-term debt	7,000	8,436
Total current liabilities	1,229,599	696,533
Long-term debt, net of current maturities	3,529,158	3,528,100
Deferred credits and other liabilities:
Deferred income tax liabilities, net	428,127	408,624
Regulatory liabilities, non-current	497,810	507,659
Benefit plan liabilities	150,979	150,556
Other deferred credits and other liabilities	135,224	134,667
Total deferred credits and other liabilities	1,212,140	1,201,506
Commitments, contingencies and guarantees (Note 3)
Equity:
Common stock $1 par value; 100,000,000 shares authorized; issued 62,909,973 and 62,827,179 shares, respectively	62,910	62,827
Additional paid-in capital	1,658,957	1,657,285
Retained earnings	931,538	870,738
Treasury stock, at cost – 39,940 and 32,492 shares, respectively	(2,564)	(2,119)
Accumulated other comprehensive income (loss)	(26,328)	(27,346)
Total stockholders’ equity	2,624,513	2,561,385
Noncontrolling interest	100,789	101,262
Total equity	2,725,302	2,662,647
TOTAL LIABILITIES AND TOTAL EQUITY	$ 8,696,199	$ 8,088,786

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares	Mar. 31, 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	62,909,973	62,827,179
Treasury stock, shares	39,940	32,492

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities:
Net income	$ 100,487	$ 97,224
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation, depletion and amortization	57,269	56,402
Deferred financing cost amortization	2,214	2,237
Impairment of investment	0	6,859
Stock compensation	3,257	291
Deferred income taxes	153	21,876
Employee benefit plans	2,304	1,235
Other adjustments, net	6,151	892
Changes in certain operating assets and liabilities:
Materials, supplies and fuel	15,932	19,222
Accounts receivable and other current assets	(11,599)	8,171
Accounts payable and other current liabilities	(23,602)	(43,297)
Regulatory assets	(533,006)	20,679
Regulatory liabilities	(5,291)	1,316
Other operating activities, net	(355)	(1,138)
Net cash provided by (used in) operating activities	(386,086)	191,969
Investing activities:
Property, plant and equipment additions	(146,302)	(171,882)
Other investing activities	78	(1,202)
Net cash (used in) investing activities	(146,224)	(173,084)
Financing activities:
Dividends paid on common stock	(35,514)	(32,902)
Common stock issued	0	99,321
Term loan - borrowings	800,000	0
Term loan - repayments	(200,000)	0
Net (payments) borrowings of Revolving Credit Facility and CP Program	(18,170)	(30,375)
Long-term debt - repayments	(1,436)	(4,291)
Distributions to noncontrolling interest	(4,644)	(4,741)
Other financing activities	(740)	(1,391)
Net cash provided by financing activities	539,496	25,621
Net change in cash, restricted cash and cash equivalents	7,186	44,506
Cash, restricted cash and cash equivalents at beginning of period	10,739	13,658
Cash, restricted cash and cash equivalents at end of period	17,925	58,164
Supplemental cash flow information:
Interest, net of amounts capitalized	(21,232)	(21,776)
Income taxes	990	0
Accrued property, plant and equipment purchases at March 31	$ 51,914	$ 53,011

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	$ (207)	$ 61,481	$ (267)	$ 1,552,788	$ 778,776	$ (207)	$ (30,655)	$ 101,946
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	97,224					93,174			4,050
Other comprehensive income (loss), 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 noncontrolling 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		$ 62,773	$ (1,925)	1,652,861	838,841		(29,382)	101,255
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 (loss), 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 noncontrolling 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

Condensed Consolidated Statem_6

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

Management's Statement_

Management's Statement:	3 Months Ended
	Mar. 31, 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 March 31, 2021, December 31, 2020 and March 31, 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 months ended March 31, 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:	3 Months Ended
	Mar. 31, 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 As of March 31, 2021 December 31, 2020 Regulatory assets Winter Storm Uri (a) $ 480,842 $ — Deferred energy and fuel cost adjustments (a) (b) 68,402 39,035 Deferred gas cost adjustments (a) (b) 17,066 3,200 Gas price derivatives (b) 324 2,226 Deferred taxes on AFUDC (c) 7,469 7,491 Employee benefit plans and related deferred taxes (d) 117,886 116,598 Environmental (b) 1,413 1,413 Loss on reacquired debt (b) 22,386 22,864 Deferred taxes on flow through accounting (d) 51,823 47,515 Decommissioning costs (c) 7,827 8,988 Gas supply contract termination (b) 1,013 2,524 Other regulatory assets (b) 25,806 26,404 Total regulatory assets 802,257 278,258 Less current regulatory assets (129,951) (51,676) Regulatory assets, non-current $ 672,306 $ 226,582 Regulatory liabilities Deferred energy and gas costs (b) $ 426 $ 13,253 Employee benefit plan costs and related deferred taxes (d) 40,471 40,256 Cost of removal (b) 177,003 172,902 Excess deferred income taxes (d) 271,492 285,259 Other regulatory liabilities (d) 21,998 21,050 Total regulatory liabilities 511,390 532,720 Less current regulatory liabilities (13,580) (25,061) Regulatory liabilities, non-current $ 497,810 $ 507,659 __________ (a) We are in discussions with our regulators regarding the timing of Winter Storm Uri incremental cost recovery. 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 significant 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, our net pre-tax incremental fuel, purchased power and natural gas costs during the three months ended March 31, 2021 were approximately $571 million. This amount does not include potential pipeline transportation charges for certain suppliers who have requested and received approval from FERC to delay billings. Our Utilities have regulatory mechanisms to recover approximately $559 million of incremental costs from Winter Storm Uri. However, given the extraordinary impact of these higher costs to our customers, our regulators are performing a heightened review. We are engaged with our regulators to identify appropriate periods over which to recover incremental costs with consideration of the impacts to our customers’ bills. We expect to recover most of the Winter Storm Uri incremental costs through a separately tracked regulatory mechanism but we also anticipate recovery of a portion of the costs through existing mechanisms. For the three months ended March 31, 2021, we expensed $12.5 million of Winter Storm Uri net incremental costs as a result of negative impacts to our Utilities and financing costs partially offset by favorable impacts to our Power Generation segment. Our Electric Utilities incurred a $3.2 million negative impact to our regulated wholesale power margins due to higher fuel costs and $2.1 million of incremental fuel costs that are not recoverable through our fuel cost recovery mechanisms. Black Hills Energy Services offers fixed contract pricing for non-regulated gas supply services to our regulated natural gas customers and the $8.2 million increase in cost of natural gas sold during Winter Storm Uri is not recoverable through the regulatory construct. Additionally, we incurred $0.7 million of interest expense for the three months ended March 31, 2021, related to our $800 million term loan which is discussed in Note 5 . Our non-regulated Power Generation segment benefited from a $1.7 million favorable impact to operating income from Winter Storm Uri. Winter Storm Uri Costs by Jurisdiction As of March 31, 2021, our estimate of incremental costs from Winter Storm Uri which was recorded to a regulatory asset is shown below by jurisdiction. This information is based on anticipated filings that we expect to complete in the second quarter of 2021 and is subject to adjustments as applications are submitted and final decisions are issued. Costs by Jurisdiction (in thousands) Gas Utilities: Arkansas Gas $ 137,500 Colorado Gas 77,850 Iowa Gas 95,450 Kansas Gas 87,900 Nebraska Gas 79,750 Wyoming Gas 29,409 Gas Utilities Total $ 507,859 Electric Utilities: Colorado Electric $ 25,500 South Dakota Electric 22,200 Wyoming Electric 3,266 Electric Utilities Total $ 50,966 Total Winter Storm Uri Incremental Costs Recorded to Regulatory Asset $ 558,825 Costs by Regulatory Asset Winter Storm Uri (a) $ 480,842 Deferred energy and fuel cost adjustments 27,166 Deferred gas cost adjustments (b) 50,817 $ 558,825 __________ (a) We expect to recover most of the Winter Storm Uri incremental costs through a separately tracked regulatory mechanism but also expect to recover a portion through our existing mechanisms. (b) Incremental natural gas costs from Winter Storm Uri are reflected as an increase in the Deferred gas cost adjustments regulatory asset, net of existing Deferred energy and gas cost regulatory liabilities, for the three months ended March 31, 2021. 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. These 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 months ended March 31, 2021. 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, are expected to be delivered to customers in the second quarter of 2021. These bill credits, which will result in a reduction in revenue, will be offset by a reduction in income tax expense and will result in a minimal impact to Net income. Colorado Gas Rate Review On September 11, 2020, Colorado Gas filed a rate review with the CPUC seeking recovery on significant infrastructure investments in its 7,000-mile natural gas pipeline system. On January 6, 2021, the CPUC issued an Order dismissing the rate review. Colorado Gas plans to file a rate review in the second quarter of 2021. On September 11, 2020, in accordance with the final order from the earlier rate review filed 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. A decision from the CPUC is expected by mid-2021. 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:	3 Months Ended
	Mar. 31, 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:	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Revenue	Revenue 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 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 months ended March 31, 2021 and 2020. Sales tax and other similar taxes are excluded from revenues. Three Months Ended March 31, 2021 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 198,500 $ 341,605 $ — $ 14,083 $ (7,107) $ 547,081 Transportation — 47,951 — — (110) 47,841 Wholesale 5,922 — 28,692 — (24,451) 10,163 Market - off-system sales 7,656 73 — — (2,884) 4,845 Transmission/Other 15,193 10,390 — — (5,296) 20,287 Revenue from contracts with customers $ 227,271 $ 400,019 $ 28,692 $ 14,083 $ (39,848) $ 630,217 Other revenues 137 2,500 471 589 (482) 3,215 Total revenues $ 227,408 $ 402,519 $ 29,163 $ 14,672 $ (40,330) $ 633,432 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 14,083 $ (7,107) $ 6,976 Services transferred over time 227,271 400,019 28,692 — (32,741) 623,241 Revenue from contracts with customers $ 227,271 $ 400,019 $ 28,692 $ 14,083 $ (39,848) $ 630,217 Three Months Ended March 31, 2020 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer Types: Retail $ 148,640 $ 298,247 $ — $ 14,403 $ (7,839) $ 453,451 Transportation — 44,108 — — (139) 43,969 Wholesale 5,552 — 25,467 — (23,612) 7,407 Market - off-system sales 4,867 138 — — (2,639) 2,366 Transmission/Other 14,857 12,572 — — (4,413) 23,016 Revenue from contracts with customers $ 173,916 $ 355,065 $ 25,467 $ 14,403 $ (38,642) $ 530,209 Other revenues 223 5,708 499 802 (391) 6,841 Total Revenues $ 174,139 $ 360,773 $ 25,966 $ 15,205 $ (39,033) $ 537,050 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 14,403 $ (7,839) $ 6,564 Services transferred over time 173,916 355,065 25,467 — (30,803) 523,645 Revenue from contracts with customers $ 173,916 $ 355,065 $ 25,467 $ 14,403 $ (38,642) $ 530,209 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:	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Debt Disclosure [Text Block]	Financing Short-term debt We had the following Notes payable outstanding in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: March 31, 2021 December 31, 2020 Balance Outstanding Letters of Credit (a) Balance Outstanding Letters of Credit (a) Term Loan $ 600,000 $ — $ — $ — Revolving Credit Facility — 16,629 — 24,730 CP Program 215,870 — 234,040 — Total Notes payable $ 815,870 $ 16,629 $ 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. Term Loan On February 24, 2021, we entered into a nine-month, $800 million unsecured term loan to provide additional liquidity and meet our cash needs related to the incremental fuel, purchased power and natural gas costs from Winter Storm Uri. The term loan, which matures on November 24, 2021, has an interest rate based on LIBOR plus 75 basis points, carries no prepayment penalty and is 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. The interest rate on term loan borrowings on March 31, 2021 was 0.86%. We expect to refinance a portion of the term loan with longer-term debt prior to maturity. In the event we are unable to refinance the remaining obligation, we believe it is probable that our current plans to manage liquidity would be sufficient to meet our obligations. Revolving Credit Facility and CP Program Our net short-term borrowings related to our Revolving Credit Facility and CP Program during the three months ended March 31, 2021 decreased by $18 million. The weighted average interest rate on short-term borrowings related to our Revolving Credit Facility and CP Program at March 31, 2021 was 0.23%. Debt Covenants Under our Revolving Credit Facility and term loan agreements, 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 noncontrolling 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 March 31, 2021: As of March 31, 2021 Covenant Requirement Consolidated Indebtedness to Capitalization Ratio 62.6% Less than 65%

Earnings Per Share_

Earnings Per Share:	3 Months Ended
	Mar. 31, 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): Three Months Ended March 31, 2021 2020 Net income available for common stock $ 96,316 $ 93,174 Weighted average shares - basic 62,633 61,778 Dilutive effect of: Equity compensation 58 78 Weighted average shares - diluted 62,691 61,856 Earnings per share of common stock: Earnings per share, Basic $ 1.54 $ 1.51 Earnings per share, Diluted $ 1.54 $ 1.51 The following securities were excluded from the diluted earnings per share computation because of their anti-dilutive nature (in thousands): Three Months Ended March 31, 2021 2020 Equity compensation 14 12 Restricted stock 19 26 Anti-dilutive shares 33 38

Risk Management and Derivatives

Risk Management and Derivatives:	3 Months Ended
	Mar. 31, 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 Winter Storm Uri, weather, 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 customer’s 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 plants 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 April 2021 through August 2023. 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: March 31, 2021 December 31, 2020 Units Notional Maximum Term (months) (a) Notional Maximum Term (months) (a) Natural gas futures purchased MMBtus — 0 620,000 3 Natural gas options purchased, net MMBtus — 0 3,160,000 3 Natural gas basis swaps purchased MMBtus — 0 900,000 3 Natural gas over-the-counter swaps, net (b) MMBtus 3,590,000 29 3,850,000 17 Natural gas physical contracts, net (c) MMBtus 3,107,817 12 17,513,061 22 Electric wholesale contracts (c) MWh 183,025 9 219,000 12 __________ (a) Term reflects the maximum forward period hedged. (b) As of March 31, 2021, 442,900 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 March 31, 2021, the Company posted $1.4 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 that allow us to settle positive and negative positions. The following table presents the fair value and balance sheet classification of our derivative instruments (in thousands) as of: Balance Sheet Location March 31, 2021 December 31, 2020 Derivatives designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 285 $ 181 Noncurrent commodity derivatives Other assets, non-current 4 43 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current — (108) Noncurrent commodity derivatives Other deferred credits and other liabilities — — Total derivatives designated as hedges $ 289 $ 116 Derivatives not designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 1,632 $ 1,667 Noncurrent commodity derivatives Other assets, non-current 32 151 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current (2,526) (1,936) Noncurrent commodity derivatives Other deferred credits and other liabilities (43) — Total derivatives not designated as hedges $ (905) $ (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 months ended March 31, 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 March 31, Three Months Ended March 31, 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 $ 713 $ 713 Interest expense $ (713) $ (713) Commodity derivatives 173 257 Fuel, purchased power and cost of natural gas sold (31) (486) Total $ 886 $ 970 $ (744) $ (1,199) As of March 31, 2021, $0.9 million of net losses related to our interest rate swaps and commodity derivatives are expected to be reclassified from AOCI into earnings 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 months ended March 31, 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 March 31, 2021 2020 Derivatives Not Designated as Hedging Instruments Income Statement Location Amount of Gain/(Loss) on Derivatives Recognized in Income (in thousands) Commodity derivatives - Electric Fuel, purchased power and cost of natural gas sold $ (1,524) $ 1,362 Commodity derivatives - Natural Gas Fuel, purchased power and cost of natural gas sold 366 766 $ (1,158) $ 2,128 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 included in our Regulatory asset or Regulatory liability related to the hedges in our Gas Utilities were $0.3 million and $2.2 million as of March 31, 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:	3 Months Ended
	Mar. 31, 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 March 31, 2021 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Total (in thousands) Assets: Commodity derivatives — Gas Utilities $ — $ 1,389 $ — $ — $ 1,389 Commodity derivatives — Electric Utilities $ — $ 564 $ — $ — $ 564 Total $ — $ 1,953 $ — $ — $ 1,953 Liabilities: Commodity derivatives — Gas Utilities $ — $ 625 $ — $ — $ 625 Commodity derivatives — Electric Utilities $ — $ 1,944 $ — $ — $ 1,944 Total $ — $ 2,569 $ — $ — $ 2,569 As of December 31, 2020 Level 1 Level 2 Level 3 Cash Collateral and Counterparty 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 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: March 31, 2021 December 31, 2020 Carrying Fair Value Carrying Fair Value Long-term debt, including current maturities (a) $ 3,536,158 $ 3,938,977 $ 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:	3 Months Ended
	Mar. 31, 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 March 31, 2021 2020 Gains and (losses) on cash flow hedges: Interest rate swaps Interest expense $ (713) $ (713) Commodity contracts Fuel, purchased power and cost of natural gas sold (31) (486) (744) (1,199) Income tax Income tax benefit 198 285 Total reclassification adjustments related to cash flow hedges, net of tax $ (546) $ (914) Amortization of components of defined benefit plans: Prior service cost Operations and maintenance $ 25 $ 30 Actuarial gain (loss) Operations and maintenance (598) (597) (573) (567) Income tax Income tax benefit 208 88 Total reclassification adjustments related to defined benefit plans, net of tax $ (365) $ (479) Total reclassifications $ (911) $ (1,393) 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 — 107 — 107 Amounts reclassified from AOCI 523 23 365 911 As of March 31, 2021 $ (12,035) $ 132 $ (14,425) $ (26,328) 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 — (175) 55 (120) Amounts reclassified from AOCI 543 371 479 1,393 As of March 31, 2020 $ (14,579) $ (260) $ (14,543) $ (29,382)

Employee Benefit Plans_

Employee Benefit Plans:	3 Months Ended
	Mar. 31, 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 March 31, 2021 2020 Service cost $ 1,259 $ 1,353 Interest cost 2,328 3,357 Expected return on plan assets (5,219) (5,648) Net loss (gain) 1,829 2,093 Net periodic benefit cost $ 197 $ 1,155 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 March 31, 2021 2020 Service cost $ 559 $ 514 Interest cost 265 412 Expected return on plan assets (34) (45) Prior service cost (benefit) (109) (137) Net loss (gain) 117 5 Net periodic benefit cost $ 798 $ 749 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 March 31, 2021 2020 Service cost $ 693 $ (1,370) Interest cost 177 275 Net loss (gain) 439 426 Net periodic benefit cost $ 1,309 $ (669) 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 quarter of 2021 and anticipated contributions for 2021 and 2022 are as follows (in thousands): Contributions Made Additional Contributions Contributions Three Months Ended March 31, 2021 Anticipated for 2021 Anticipated for 2022 Defined Benefit Pension Plan $ — $ — $ 3,788 Non-pension Defined Benefit Postretirement Healthcare Plan $ 1,382 $ 4,145 $ 5,241 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans $ 482 $ 1,445 $ 1,967

Income Taxes_

Income Taxes:	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Winter Storm Uri As discussed in Note 2 above, $559 million of the incremental costs from Winter Storm Uri are recoverable through our Utilities’ regulatory mechanisms, and we recorded these costs as regulatory assets at March 31, 2021. 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 $132 million at March 31, 2021. 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 an 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 2040. 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 March 31, 2021. Income Tax Benefit (Expense) and Effective Tax Rates Three Months Ended March 31, 2021 Compared to the Three Months Ended March 31, 2020 Income tax (expense) for the three months ended March 31, 2021 was $(0.5) million compared to $(16) million reported for the same period in 2020. For the three months ended March 31, 2021 the effective tax rate was 0.5% compared to 14.1% for the same period in 2020. The lower effective tax rate is primarily due to $7.6 million of increased tax benefits from Colorado Electric’s TCJA-related bill credits to customers (which is offset by reduced revenue), $1.5 million of increased tax benefits from amortization of excess deferred income taxes and $1.3 million of increased tax benefits from federal production tax credits associated with new wind assets.

Business Segment Information_

Business Segment Information:	3 Months Ended
	Mar. 31, 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 Chief Operating Decision Maker (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: March 31, 2021 December 31, 2020 Electric Utilities $ 3,217,474 $ 3,120,928 Gas Utilities 4,900,939 4,376,204 Power Generation 406,742 404,220 Mining 76,097 77,085 Corporate and Other 94,947 110,349 Total assets $ 8,696,199 $ 8,088,786 Three Months Ended March 31, 2021 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 220,500 $ 137 $ 6,771 $ — $ 227,408 Gas Utilities 398,499 2,408 1,520 92 402,519 Power Generation 4,241 421 24,451 50 29,163 Mining 6,977 249 7,106 340 14,672 Inter-company eliminations — — (39,848) (482) (40,330) Total $ 630,217 $ 3,215 $ — $ — $ 633,432 Three Months Ended March 31, 2020 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 167,503 $ 223 $ 6,413 $ — $ 174,139 Gas Utilities 354,287 5,708 778 — 360,773 Power Generation 1,855 443 23,612 56 25,966 Mining 6,564 467 7,839 335 15,205 Inter-company eliminations — — (38,642) (391) (39,033) Total $ 530,209 $ 6,841 $ — $ — $ 537,050 Three Months Ended March 31, 2021 2020 Adjusted operating income: Electric Utilities $ 21,813 $ 35,650 Gas Utilities 102,094 102,897 Power Generation 14,269 11,349 Mining 3,261 3,129 Corporate and Other (3,122) 160 Operating income 138,315 153,185 Interest expense, net (37,600) (35,453) Impairment of investment — (6,859) Other income (expense), net 266 2,353 Income tax (expense) (494) (16,002) Net income 100,487 97,224 Net income attributable to noncontrolling interest (4,171) (4,050) Net income available for common stock $ 96,316 $ 93,174

Selected Balance Sheet Informat

Selected Balance Sheet Information:	3 Months Ended
	Mar. 31, 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: March 31, 2021 December 31, 2020 Accounts receivable, trade $ 199,548 $ 146,899 Unbilled revenue 91,085 126,065 Less: Allowance for credit losses (8,251) (7,003) Accounts receivable, net $ 282,382 $ 265,961 Changes to allowance for credit losses for the three months ended March 31, 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 March 31, 2021 $ 7,003 $ 1,877 $ 1,014 $ (1,643) $ 8,251 2020 $ 2,444 $ 3,519 $ 922 $ (1,723) $ 5,162 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: March 31, 2021 December 31, 2020 Materials and supplies $ 88,088 $ 85,250 Fuel - Electric Utilities 1,590 1,531 Natural gas in storage 12,925 30,619 Total materials, supplies and fuel $ 102,603 $ 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: March 31, 2021 December 31, 2020 Accrued employee compensation, benefits and withholdings $ 57,347 $ 77,806 Accrued property taxes 49,267 47,105 Customer deposits and prepayments 50,194 52,185 Accrued interest 45,896 31,520 Other (none of which is individually significant) 27,740 34,996 Total accrued liabilities $ 230,444 $ 243,612

Management's Statement (Policie

Management's Statement (Policies)	3 Months Ended
	Mar. 31, 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 March 31, 2021, December 31, 2020 and March 31, 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)	3 Months Ended
	Mar. 31, 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 As of March 31, 2021 December 31, 2020 Regulatory assets Winter Storm Uri (a) $ 480,842 $ — Deferred energy and fuel cost adjustments (a) (b) 68,402 39,035 Deferred gas cost adjustments (a) (b) 17,066 3,200 Gas price derivatives (b) 324 2,226 Deferred taxes on AFUDC (c) 7,469 7,491 Employee benefit plans and related deferred taxes (d) 117,886 116,598 Environmental (b) 1,413 1,413 Loss on reacquired debt (b) 22,386 22,864 Deferred taxes on flow through accounting (d) 51,823 47,515 Decommissioning costs (c) 7,827 8,988 Gas supply contract termination (b) 1,013 2,524 Other regulatory assets (b) 25,806 26,404 Total regulatory assets 802,257 278,258 Less current regulatory assets (129,951) (51,676) Regulatory assets, non-current $ 672,306 $ 226,582 Regulatory liabilities Deferred energy and gas costs (b) $ 426 $ 13,253 Employee benefit plan costs and related deferred taxes (d) 40,471 40,256 Cost of removal (b) 177,003 172,902 Excess deferred income taxes (d) 271,492 285,259 Other regulatory liabilities (d) 21,998 21,050 Total regulatory liabilities 511,390 532,720 Less current regulatory liabilities (13,580) (25,061) Regulatory liabilities, non-current $ 497,810 $ 507,659 __________ (a) We are in discussions with our regulators regarding the timing of Winter Storm Uri incremental cost recovery. 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.
February 2021 Winter Storm Uri Fuel Costs	As of March 31, 2021, our estimate of incremental costs from Winter Storm Uri which was recorded to a regulatory asset is shown below by jurisdiction. This information is based on anticipated filings that we expect to complete in the second quarter of 2021 and is subject to adjustments as applications are submitted and final decisions are issued. Costs by Jurisdiction (in thousands) Gas Utilities: Arkansas Gas $ 137,500 Colorado Gas 77,850 Iowa Gas 95,450 Kansas Gas 87,900 Nebraska Gas 79,750 Wyoming Gas 29,409 Gas Utilities Total $ 507,859 Electric Utilities: Colorado Electric $ 25,500 South Dakota Electric 22,200 Wyoming Electric 3,266 Electric Utilities Total $ 50,966 Total Winter Storm Uri Incremental Costs Recorded to Regulatory Asset $ 558,825 Costs by Regulatory Asset Winter Storm Uri (a) $ 480,842 Deferred energy and fuel cost adjustments 27,166 Deferred gas cost adjustments (b) 50,817 $ 558,825 __________ (a) We expect to recover most of the Winter Storm Uri incremental costs through a separately tracked regulatory mechanism but also expect to recover a portion through our existing mechanisms. (b) Incremental natural gas costs from Winter Storm Uri are reflected as an increase in the Deferred gas cost adjustments regulatory asset, net of existing Deferred energy and gas cost regulatory liabilities, for the three months ended March 31, 2021.

Revenue (Tables)

Revenue (Tables)	3 Months Ended
	Mar. 31, 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 months ended March 31, 2021 and 2020. Sales tax and other similar taxes are excluded from revenues. Three Months Ended March 31, 2021 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 198,500 $ 341,605 $ — $ 14,083 $ (7,107) $ 547,081 Transportation — 47,951 — — (110) 47,841 Wholesale 5,922 — 28,692 — (24,451) 10,163 Market - off-system sales 7,656 73 — — (2,884) 4,845 Transmission/Other 15,193 10,390 — — (5,296) 20,287 Revenue from contracts with customers $ 227,271 $ 400,019 $ 28,692 $ 14,083 $ (39,848) $ 630,217 Other revenues 137 2,500 471 589 (482) 3,215 Total revenues $ 227,408 $ 402,519 $ 29,163 $ 14,672 $ (40,330) $ 633,432 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 14,083 $ (7,107) $ 6,976 Services transferred over time 227,271 400,019 28,692 — (32,741) 623,241 Revenue from contracts with customers $ 227,271 $ 400,019 $ 28,692 $ 14,083 $ (39,848) $ 630,217 Three Months Ended March 31, 2020 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer Types: Retail $ 148,640 $ 298,247 $ — $ 14,403 $ (7,839) $ 453,451 Transportation — 44,108 — — (139) 43,969 Wholesale 5,552 — 25,467 — (23,612) 7,407 Market - off-system sales 4,867 138 — — (2,639) 2,366 Transmission/Other 14,857 12,572 — — (4,413) 23,016 Revenue from contracts with customers $ 173,916 $ 355,065 $ 25,467 $ 14,403 $ (38,642) $ 530,209 Other revenues 223 5,708 499 802 (391) 6,841 Total Revenues $ 174,139 $ 360,773 $ 25,966 $ 15,205 $ (39,033) $ 537,050 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 14,403 $ (7,839) $ 6,564 Services transferred over time 173,916 355,065 25,467 — (30,803) 523,645 Revenue from contracts with customers $ 173,916 $ 355,065 $ 25,467 $ 14,403 $ (38,642) $ 530,209

Financing (Tables)

Financing (Tables)	3 Months Ended
	Mar. 31, 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: March 31, 2021 December 31, 2020 Balance Outstanding Letters of Credit (a) Balance Outstanding Letters of Credit (a) Term Loan $ 600,000 $ — $ — $ — Revolving Credit Facility — 16,629 — 24,730 CP Program 215,870 — 234,040 — Total Notes payable $ 815,870 $ 16,629 $ 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 March 31, 2021: As of March 31, 2021 Covenant Requirement Consolidated Indebtedness to Capitalization Ratio 62.6% Less than 65%

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 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): Three Months Ended March 31, 2021 2020 Net income available for common stock $ 96,316 $ 93,174 Weighted average shares - basic 62,633 61,778 Dilutive effect of: Equity compensation 58 78 Weighted average shares - diluted 62,691 61,856 Earnings per share of common stock: Earnings per share, Basic $ 1.54 $ 1.51 Earnings per share, Diluted $ 1.54 $ 1.51
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 March 31, 2021 2020 Equity compensation 14 12 Restricted stock 19 26 Anti-dilutive shares 33 38

Risk Management and Derivativ_2

Risk Management and Derivatives (Tables)	3 Months Ended
	Mar. 31, 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: March 31, 2021 December 31, 2020 Units Notional Maximum Term (months) (a) Notional Maximum Term (months) (a) Natural gas futures purchased MMBtus — 0 620,000 3 Natural gas options purchased, net MMBtus — 0 3,160,000 3 Natural gas basis swaps purchased MMBtus — 0 900,000 3 Natural gas over-the-counter swaps, net (b) MMBtus 3,590,000 29 3,850,000 17 Natural gas physical contracts, net (c) MMBtus 3,107,817 12 17,513,061 22 Electric wholesale contracts (c) MWh 183,025 9 219,000 12 __________ (a) Term reflects the maximum forward period hedged. (b) As of March 31, 2021, 442,900 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 March 31, 2021 December 31, 2020 Derivatives designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 285 $ 181 Noncurrent commodity derivatives Other assets, non-current 4 43 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current — (108) Noncurrent commodity derivatives Other deferred credits and other liabilities — — Total derivatives designated as hedges $ 289 $ 116 Derivatives not designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 1,632 $ 1,667 Noncurrent commodity derivatives Other assets, non-current 32 151 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current (2,526) (1,936) Noncurrent commodity derivatives Other deferred credits and other liabilities (43) — Total derivatives not designated as hedges $ (905) $ (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 months ended March 31, 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 March 31, Three Months Ended March 31, 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 $ 713 $ 713 Interest expense $ (713) $ (713) Commodity derivatives 173 257 Fuel, purchased power and cost of natural gas sold (31) (486) Total $ 886 $ 970 $ (744) $ (1,199) The following table summarizes the impacts of derivative instruments not designated as hedge instruments on our Condensed Consolidated Statements of Income for the three months ended March 31, 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 March 31, 2021 2020 Derivatives Not Designated as Hedging Instruments Income Statement Location Amount of Gain/(Loss) on Derivatives Recognized in Income (in thousands) Commodity derivatives - Electric Fuel, purchased power and cost of natural gas sold $ (1,524) $ 1,362 Commodity derivatives - Natural Gas Fuel, purchased power and cost of natural gas sold 366 766 $ (1,158) $ 2,128

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2021 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Total (in thousands) Assets: Commodity derivatives — Gas Utilities $ — $ 1,389 $ — $ — $ 1,389 Commodity derivatives — Electric Utilities $ — $ 564 $ — $ — $ 564 Total $ — $ 1,953 $ — $ — $ 1,953 Liabilities: Commodity derivatives — Gas Utilities $ — $ 625 $ — $ — $ 625 Commodity derivatives — Electric Utilities $ — $ 1,944 $ — $ — $ 1,944 Total $ — $ 2,569 $ — $ — $ 2,569 As of December 31, 2020 Level 1 Level 2 Level 3 Cash Collateral and Counterparty 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
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: March 31, 2021 December 31, 2020 Carrying Fair Value Carrying Fair Value Long-term debt, including current maturities (a) $ 3,536,158 $ 3,938,977 $ 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)	3 Months Ended
	Mar. 31, 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 March 31, 2021 2020 Gains and (losses) on cash flow hedges: Interest rate swaps Interest expense $ (713) $ (713) Commodity contracts Fuel, purchased power and cost of natural gas sold (31) (486) (744) (1,199) Income tax Income tax benefit 198 285 Total reclassification adjustments related to cash flow hedges, net of tax $ (546) $ (914) Amortization of components of defined benefit plans: Prior service cost Operations and maintenance $ 25 $ 30 Actuarial gain (loss) Operations and maintenance (598) (597) (573) (567) Income tax Income tax benefit 208 88 Total reclassification adjustments related to defined benefit plans, net of tax $ (365) $ (479) Total reclassifications $ (911) $ (1,393)
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 — 107 — 107 Amounts reclassified from AOCI 523 23 365 911 As of March 31, 2021 $ (12,035) $ 132 $ (14,425) $ (26,328) 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 — (175) 55 (120) Amounts reclassified from AOCI 543 371 479 1,393 As of March 31, 2020 $ (14,579) $ (260) $ (14,543) $ (29,382)

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2021 2020 Service cost $ 1,259 $ 1,353 Interest cost 2,328 3,357 Expected return on plan assets (5,219) (5,648) Net loss (gain) 1,829 2,093 Net periodic benefit cost $ 197 $ 1,155 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 March 31, 2021 2020 Service cost $ 559 $ 514 Interest cost 265 412 Expected return on plan assets (34) (45) Prior service cost (benefit) (109) (137) Net loss (gain) 117 5 Net periodic benefit cost $ 798 $ 749 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 March 31, 2021 2020 Service cost $ 693 $ (1,370) Interest cost 177 275 Net loss (gain) 439 426 Net periodic benefit cost $ 1,309 $ (669)
Schedule of Defined Benefit Plans Contributions	Contributions made in the first quarter of 2021 and anticipated contributions for 2021 and 2022 are as follows (in thousands): Contributions Made Additional Contributions Contributions Three Months Ended March 31, 2021 Anticipated for 2021 Anticipated for 2022 Defined Benefit Pension Plan $ — $ — $ 3,788 Non-pension Defined Benefit Postretirement Healthcare Plan $ 1,382 $ 4,145 $ 5,241 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans $ 482 $ 1,445 $ 1,967

Business Segment Information (T

Business Segment Information (Tables)	3 Months Ended
	Mar. 31, 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: March 31, 2021 December 31, 2020 Electric Utilities $ 3,217,474 $ 3,120,928 Gas Utilities 4,900,939 4,376,204 Power Generation 406,742 404,220 Mining 76,097 77,085 Corporate and Other 94,947 110,349 Total assets $ 8,696,199 $ 8,088,786 Three Months Ended March 31, 2021 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 220,500 $ 137 $ 6,771 $ — $ 227,408 Gas Utilities 398,499 2,408 1,520 92 402,519 Power Generation 4,241 421 24,451 50 29,163 Mining 6,977 249 7,106 340 14,672 Inter-company eliminations — — (39,848) (482) (40,330) Total $ 630,217 $ 3,215 $ — $ — $ 633,432 Three Months Ended March 31, 2020 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 167,503 $ 223 $ 6,413 $ — $ 174,139 Gas Utilities 354,287 5,708 778 — 360,773 Power Generation 1,855 443 23,612 56 25,966 Mining 6,564 467 7,839 335 15,205 Inter-company eliminations — — (38,642) (391) (39,033) Total $ 530,209 $ 6,841 $ — $ — $ 537,050 Three Months Ended March 31, 2021 2020 Adjusted operating income: Electric Utilities $ 21,813 $ 35,650 Gas Utilities 102,094 102,897 Power Generation 14,269 11,349 Mining 3,261 3,129 Corporate and Other (3,122) 160 Operating income 138,315 153,185 Interest expense, net (37,600) (35,453) Impairment of investment — (6,859) Other income (expense), net 266 2,353 Income tax (expense) (494) (16,002) Net income 100,487 97,224 Net income attributable to noncontrolling interest (4,171) (4,050) Net income available for common stock $ 96,316 $ 93,174

Selected Balance Sheet Inform_2

Selected Balance Sheet Information (Tables)	3 Months Ended
	Mar. 31, 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: March 31, 2021 December 31, 2020 Accounts receivable, trade $ 199,548 $ 146,899 Unbilled revenue 91,085 126,065 Less: Allowance for credit losses (8,251) (7,003) Accounts receivable, net $ 282,382 $ 265,961
Financing Receivable, Current, Allowance for Credit Loss	Changes to allowance for credit losses for the three months ended March 31, 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 March 31, 2021 $ 7,003 $ 1,877 $ 1,014 $ (1,643) $ 8,251 2020 $ 2,444 $ 3,519 $ 922 $ (1,723) $ 5,162
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: March 31, 2021 December 31, 2020 Materials and supplies $ 88,088 $ 85,250 Fuel - Electric Utilities 1,590 1,531 Natural gas in storage 12,925 30,619 Total materials, supplies and fuel $ 102,603 $ 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: March 31, 2021 December 31, 2020 Accrued employee compensation, benefits and withholdings $ 57,347 $ 77,806 Accrued property taxes 49,267 47,105 Customer deposits and prepayments 50,194 52,185 Accrued interest 45,896 31,520 Other (none of which is individually significant) 27,740 34,996 Total accrued liabilities $ 230,444 $ 243,612

Regulatory Matters (Details)

Regulatory Matters (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Regulatory assets
Regulatory assets	$ 802,257	$ 278,258
Less current regulatory assets	(129,951)	(51,676)
Regulatory assets, non-current	672,306	226,582
Regulatory liabilities
Regulatory liabilities	511,390	532,720
Less current regulatory liabilities	(13,580)	(25,061)
Regulatory liabilities, non-current	497,810	507,659
Deferred energy and gas costs
Regulatory liabilities
Regulatory liabilities	426	13,253
Employee benefit plans
Regulatory liabilities
Regulatory liabilities	40,471	40,256
Cost of removal
Regulatory liabilities
Regulatory liabilities	177,003	172,902
Excess deferred income taxes
Regulatory liabilities
Regulatory liabilities	271,492	285,259
Other regulatory liabilities
Regulatory liabilities
Regulatory liabilities	21,998	21,050
Deferred energy and gas costs
Regulatory assets
Regulatory assets	68,402	39,035
Deferred gas cost adjustments
Regulatory assets
Regulatory assets	17,066	3,200
Gas price derivatives
Regulatory assets
Regulatory assets	324	2,226
Deferred taxes on AFUDC
Regulatory assets
Regulatory assets	7,469	7,491
Employee benefit plans
Regulatory assets
Regulatory assets	117,886	116,598
Environmental
Regulatory assets
Regulatory assets	1,413	1,413
Loss on reacquired debt
Regulatory assets
Regulatory assets	22,386	22,864
Deferred taxes on flow through accounting
Regulatory assets
Regulatory assets	51,823	47,515
Decommissioning costs
Regulatory assets
Regulatory assets	7,827	8,988
Gas supply contract termination
Regulatory assets
Regulatory assets	1,013	2,524
Other regulatory assets
Regulatory assets
Regulatory assets	25,806	26,404
Winter Storm Uri Incremental Costs in a Separately Tracked Mechanism
Regulatory assets
Regulatory assets	$ 480,842	$ 0

Regulatory Matters_ Winter Stor

Regulatory Matters: Winter Storm Uri (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Feb. 24, 2021	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory assets	$ 802,257		$ 278,258
Winter Storm Uri Incremental Costs in a Separately Tracked Mechanism
Public Utilities, General Disclosures [Line Items]
Regulatory assets	480,842		0
Deferred energy and gas costs
Public Utilities, General Disclosures [Line Items]
Regulatory assets	68,402		39,035
Deferred gas cost adjustments
Public Utilities, General Disclosures [Line Items]
Regulatory assets	17,066		$ 3,200
Senior Unsecured Notes Due 2021
Public Utilities, General Disclosures [Line Items]
Debt Instrument, Face Amount		$ 800,000
Winter Storm Uri
Public Utilities, General Disclosures [Line Items]
Incremental Fuel, Purchased Power and Natural Gas Costs	571,000
Regulatory assets	558,825
Income Statement Impacts	12,500
Winter Storm Uri | Winter Storm Uri Incremental Costs in a Separately Tracked Mechanism
Public Utilities, General Disclosures [Line Items]
Regulatory assets	480,842
Winter Storm Uri | Deferred energy and gas costs
Public Utilities, General Disclosures [Line Items]
Regulatory assets	27,166
Winter Storm Uri | Deferred gas cost adjustments
Public Utilities, General Disclosures [Line Items]
Regulatory assets	50,817
Winter Storm Uri | Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts)
Public Utilities, General Disclosures [Line Items]
Income Statement Impacts	700
Winter Storm Uri | Electric Utilities
Public Utilities, General Disclosures [Line Items]
Regulatory assets	50,966
Winter Storm Uri | Electric Utilities | Wholesale Power Margin Impacts
Public Utilities, General Disclosures [Line Items]
Income Statement Impacts	3,200
Winter Storm Uri | Electric Utilities | Non-recoverable Fuel Costs
Public Utilities, General Disclosures [Line Items]
Income Statement Impacts	2,100
Winter Storm Uri | Electric Utilities | Colorado Electric
Public Utilities, General Disclosures [Line Items]
Regulatory assets	25,500
Winter Storm Uri | Electric Utilities | South Dakota Electric
Public Utilities, General Disclosures [Line Items]
Regulatory assets	22,200
Winter Storm Uri | Electric Utilities | Wyoming Electric
Public Utilities, General Disclosures [Line Items]
Regulatory assets	3,266
Winter Storm Uri | Gas Utilities
Public Utilities, General Disclosures [Line Items]
Regulatory assets	507,859
Winter Storm Uri | Gas Utilities | Arkansas Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	137,500
Winter Storm Uri | Gas Utilities | Colorado Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	77,850
Winter Storm Uri | Gas Utilities | Iowa Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	95,450
Winter Storm Uri | Gas Utilities | Kansas Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	87,900
Winter Storm Uri | Gas Utilities | Nebraska Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	79,750
Winter Storm Uri | Gas Utilities | Wyoming Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	29,409
Winter Storm Uri | Gas Utilities | Black Hills Energy Services | Non-recoverable Fuel Costs
Public Utilities, General Disclosures [Line Items]
Income Statement Impacts	8,200
Winter Storm Uri | Power Generation | Operating Income (Loss)
Public Utilities, General Disclosures [Line Items]
Income Statement Impacts	$ (1,700)

Regulatory Matters_ Rate Review

Regulatory Matters: Rate Review (Details) $ in Thousands	Mar. 01, 2021USD ($)	Jan. 26, 2021USD ($)mi	Sep. 11, 2020	Jan. 06, 2021mi	Dec. 30, 2020USD ($)
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
Nebraska Public Service Commission (NPSC) | Nebraska Gas
Public Utilities, General Disclosures [Line Items]
Tax Cuts and Jobs Act, Income Tax Expense (Benefit)		$ 2,900
Nebraska Publc Service Commission (NPSC) | Nebraska Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Equity Capital Structure, Percentage	50.00%
Public Utilities, Approved Debt Capital Structure, Percentage	50.00%
Public Utilities, Approved Return on Equity, Percentage	9.50%
Public Utilities, Term Extension of System Saftey and Integrity Rider	5 years
Rate Review Filed with the Regulatory Agency | Colorado Public Utilities Commission (CPUC) | Colorado Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Term Extension of System Saftey and Integrity Rider			5 years
Rate Review Filed with the 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 Amount of System Safety and Integrety Rider Moved to Base Rates	$ 4,600
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 6,500
Rate Review Dismissed by Regulatory Agency | Colorado Public Utilities Commission (CPUC) | Colorado Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities - Length of Natural Gas Pipeline to Receive Infrastructure Investments | mi				7,000

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

Disaggregation of Revenue (Deta

Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 630,217	$ 530,209
Total revenues	633,432	537,050
Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,976	6,564
Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	623,241	523,645
Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	3,215	6,841
Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	547,081	453,451
Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47,841	43,969
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10,163	7,407
Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4,845	2,366
Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	20,287	23,016
Inter-company Revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(39,848)	(38,642)
Total revenues	(40,330)	(39,033)
Inter-company Revenues | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(7,107)	(7,839)
Inter-company Revenues | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(32,741)	(30,803)
Inter-company Revenues | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(482)	(391)
Inter-company Revenues | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(7,107)	(7,839)
Inter-company Revenues | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(110)	(139)
Inter-company Revenues | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(24,451)	(23,612)
Inter-company Revenues | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(2,884)	(2,639)
Inter-company Revenues | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(5,296)	(4,413)
Electric Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	227,271	173,916
Total revenues	227,408	174,139
Electric Utilities | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Electric Utilities | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	227,271	173,916
Electric Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	137	223
Electric Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	198,500	148,640
Electric Utilities | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Electric Utilities | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5,922	5,552
Electric Utilities | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7,656	4,867
Electric Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,193	14,857
Gas Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	400,019	355,065
Total revenues	402,519	360,773
Gas Utilities | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Gas Utilities | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	400,019	355,065
Gas Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	2,500	5,708
Gas Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	341,605	298,247
Gas Utilities | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47,951	44,108
Gas Utilities | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Gas Utilities | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	73	138
Gas Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10,390	12,572
Power Generation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	28,692	25,467
Total revenues	29,163	25,966
Power Generation | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Power Generation | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	28,692	25,467
Power Generation | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	471	499
Power Generation | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Power Generation | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Power Generation | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	28,692	25,467
Power Generation | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Power Generation | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Mining
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,083	14,403
Total revenues	14,672	15,205
Mining | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,083	14,403
Mining | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Mining | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	589	802
Mining | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,083	14,403
Mining | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Mining | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Mining | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Mining | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0

Financing_ Schedule of Short-te

Financing: Schedule of Short-term Debt and Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Short-term Debt [Line Items]
Notes payable	$ 815,870	$ 234,040
Letters of Credit	16,629	24,730
Revolving Credit Facility
Short-term Debt [Line Items]
Notes payable	0	0
Letters of Credit	16,629	24,730
Term Loan
Short-term Debt [Line Items]
Notes payable	600,000	0
Letters of Credit	0	0
Commercial Paper
Short-term Debt [Line Items]
Notes payable	215,870	234,040
Letters of Credit	$ 0	$ 0

Financing_ Term Loan (Details)

Financing: Term Loan (Details) - USD ($) $ in Thousands	Feb. 24, 2021	Mar. 31, 2021	Mar. 31, 2020
Repayments of Other Short-term Debt		$ 200,000	$ 0
Senior Unsecured Notes Due 2021
Debt Instrument, Face Amount	$ 800,000
Senior Unsecured Notes Due 2021 | Line of Credit
Debt Instrument, Term	9 months
Debt Instrument, Face Amount	$ 800,000
Debt Instrument, Basis Spread on Variable Rate	75.00%
Payment for Debt Extinguishment or Debt Prepayment Cost		0
Repayments of Other Short-term Debt		$ 200,000
Short-term Debt, Percentage Bearing Variable Interest Rate		0.86%

Financing_ Revolving Credit Fac

Financing: Revolving Credit Facility and CP Program (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net (payments) borrowings of Revolving Credit Facility and CP Program	$ (18,170)	$ (30,375)
Commercial Paper
Short-term interest rate	0.23%

Financing_ Debt Covenants (Deta

Financing: Debt Covenants (Details)	Mar. 31, 2021
Line of Credit Facility [Line Items]
Ratio of Indebtedness to Net Capital	0.626
Maximum
Line of Credit Facility [Line Items]
Consolidated Indebtedness to Capitalization Ratio	0.65

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
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income available for common stock	$ 96,316	$ 93,174
Weighted average shares - basic (in shares)	62,633	61,778
Dilutive effect of:
Equity compensation (in shares)	58	78
Weighted average shares - diluted (in shares)	62,691	61,856
Earnings per share, Basic (usd per share)	$ 1.54	$ 1.51
Earnings per share, Diluted (usd per share)	$ 1.54	$ 1.51

Earnings Per Share_ Anti-diluti

Earnings Per Share: Anti-dilutive shares (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	33	38
Equity compensation - (in shares)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	14	12
Restricted Stock (in shares)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	19	26

Risk Management and Derivativ_3

Risk Management and Derivatives: Utilities (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021USD ($)MMBTUmW	Dec. 31, 2020mWMMBTU
Natural gas over-the-counter swaps, net
Derivative [Line Items]
Credit Risk Derivative Liabilities, at Fair Value | $	$ 1.4
Natural Gas, Distribution | Cash Flow Hedging
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	442,900
Natural Gas, Distribution | Natural gas futures purchased
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0	620,000
Derivative, Remaining Maturity	0 months	3 months
Natural Gas, Distribution | Natural gas options purchased, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0	3,160,000
Derivative, Remaining Maturity	0 months	3 months
Natural Gas, Distribution | Natural gas basis swaps purchased
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0	900,000
Derivative, Remaining Maturity	0 months	3 months
Natural Gas, Distribution | Natural gas over-the-counter swaps, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	3,590,000	3,850,000
Derivative, Remaining Maturity	29 months	17 months
Natural Gas, Distribution | Natural gas physical contracts, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	3,107,817	17,513,061
Derivative, Remaining Maturity	12 months	22 months
Electricity | Electric wholesale contracts
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | mW	183,025	219,000
Derivative, Remaining Maturity	9 months	12 months

Risk Management and Derivativ_4

Risk Management and Derivatives: Derivatives by Balance Sheet Classification (Details) - Commodity Contract - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair Value Hedges, Net	$ 289	$ 116
Designated as Hedging Instrument | Derivative assets — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	285	181
Designated as Hedging Instrument | Other assets, non-current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	4	43
Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	0	(108)
Designated as Hedging Instrument | Other deferred credits and other liabilities
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	0	0
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair Value Hedges, Net	(905)	(118)
Not Designated as Hedging Instrument | Derivative assets — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	1,632	1,667
Not Designated as Hedging Instrument | Other assets, non-current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	32	151
Not Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	(2,526)	(1,936)
Not Designated as Hedging Instrument | Other deferred credits and other liabilities
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	$ (43)	$ 0

Risk Management and Derivativ_5

Risk Management and Derivatives: Derivatives Designated as Hedge Instruments (Details) - Cash Flow Hedging - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (744)	$ (1,199)
Designated as Hedging Instrument
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	886	970
Interest rate swaps | Designated as Hedging Instrument
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	713	713
Commodity Contract | Designated as Hedging Instrument
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	173	257
Interest Rate Swap and Commodity Derivative
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	900
Interest Expense | Interest rate swaps
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(713)	(713)
Fuel, purchased power and cost of natural gas sold | Commodity Contract
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (31)	$ (486)

Risk Management and Derivativ_6

Risk Management and Derivatives: Derivatives Not Designated as Hedge Instruments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Derivative [Line Items]
Regulatory assets	$ 802,257		$ 278,258
Gas price derivatives
Derivative [Line Items]
Regulatory assets	324		$ 2,226
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(1,158)	$ 2,128
Not Designated as Hedging Instrument | Fuel, purchased power and cost of natural gas sold | Electricity
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(1,524)	1,362
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	$ 366	$ 766

Fair Value Measurements_ Schedu

Fair Value Measurements: Schedule of Fair Values (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
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	$ (1,527)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	0	(1,552)
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	1,953	2,042
Derivative Liabilities, Total	2,569	2,044
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, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	1,953	3,569
Derivative Liabilities, Total	2,569	3,596
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
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	0	(1,527)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	0	(1,552)
Gas Utilities | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	1,389	977
Derivative Liabilities, Fair Value Disclosure	625	1,123
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
Gas Utilities | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	1,389	2,504
Derivative Liabilities, Fair Value Disclosure	625	2,675
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
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
Electric Utilities | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	564	1,065
Derivative Liabilities, Fair Value Disclosure	1,944	921
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
Electric Utilities | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	564	1,065
Derivative Liabilities, Fair Value Disclosure	1,944	921
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	Mar. 31, 2021	Dec. 31, 2020
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 3,536,158	$ 3,536,536
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 3,938,977	$ 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
	Mar. 31, 2021	Mar. 31, 2020
Condensed Statement of Income Captions [Line Items]
Interest Expense	$ 37,825	$ 35,781
Fuel, purchased power and cost of natural gas sold	293,147	187,879
Operations and maintenance	129,679	125,466
Income before Income Taxes	100,981	113,226
Income tax benefit (expense)	(494)	(16,002)
Net income (loss)	100,487	97,224
Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Net income (loss)	(911)	(1,393)
Cash Flow Hedging | Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Income before Income Taxes	(744)	(1,199)
Income tax benefit (expense)	198	285
Net income (loss)	(546)	(914)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost | Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Operations and maintenance	25	30
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Operations and maintenance	(598)	(597)
Accumulated Defined Benefit Plans Adjustment | Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Income before Income Taxes	(573)	(567)
Income tax benefit (expense)	208	88
Net income (loss)	(365)	(479)
Interest rate swaps | Cash Flow Hedging | Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Interest Expense	(713)	(713)
Commodity Contract | Cash Flow Hedging | Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Fuel, purchased power and cost of natural gas sold	$ (31)	$ (486)

Other Comprehensive Income (Los

Other Comprehensive Income (Loss): Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 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	(26,328)	(29,382)
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	(14,425)	(14,543)
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	365	479
Accumulated Other Comprehensive Income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	107	(120)
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	911	1,393
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	(12,035)	(14,579)
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	523	543
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	107	(175)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	132	(260)
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	$ 23	$ 371

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 1,259	$ 1,353
Interest cost	2,328	3,357
Expected return on plan assets	(5,219)	(5,648)
Net loss (gain)	1,829	2,093
Net periodic benefit cost	197	1,155
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	0
Estimated Future Employer Contributions in Current Fiscal Year	0
Estimated Future Employer Contributions in Next Fiscal Year	3,788
Other Postretirement Benefits Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	559	514
Interest cost	265	412
Expected return on plan assets	(34)	(45)
Prior service cost (benefit)	(109)	(137)
Net loss (gain)	117	5
Net periodic benefit cost	798	749
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	1,382
Estimated Future Employer Contributions in Current Fiscal Year	4,145
Estimated Future Employer Contributions in Next Fiscal Year	5,241
Supplemental Non-qualified Defined Benefit and Defined Contribution Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	693	1,370
Interest cost	177	275
Net loss (gain)	439	426
Net periodic benefit cost	1,309	$ (669)
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	482
Estimated Future Employer Contributions in Current Fiscal Year	1,445
Estimated Future Employer Contributions in Next Fiscal Year	$ 1,967

Income Taxes_ Winter Storm Uri

Income Taxes: Winter Storm Uri (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Regulatory assets	$ 802,257	$ 278,258
Deferred income tax liabilities, net	428,127	$ 408,624
Winter Storm Uri
Regulatory assets	558,825
Deferred income tax liabilities, net	$ 132,000

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income tax benefit (expense)	$ (494)	$ (16,002)
Effective Tax Rate	0.50%	14.10%
Effective Income Tax Reconciliation, Tax Benefit From Amortization Of Excess Deferred Income Taxes	$ 1,500
Wind Assets
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Amount	1,300
Colorado Electric
Effective Income Tax Rate Reconciliation Tax Cuts And Jobs Act Of 2017 Amount, Tax Benefit from Bill Credit	$ 7,600

Business Segment Information_ S

Business Segment Information: Segment and Corporate Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 8,696,199	$ 8,088,786
Corporate
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	94,947	110,349
Electric Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	3,217,474	3,120,928
Gas Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	4,900,939	4,376,204
Power Generation
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	406,742	404,220
Mining
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 76,097	$ 77,085

Business Segment Information_ I

Business Segment Information: Information Relating to Segment Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information
Revenue from contracts with customers	$ 630,217	$ 530,209
Revenues	633,432	537,050
Operating income	138,315	153,185
Interest expense, net	(37,600)	(35,453)
Impairment of investment	0	(6,859)
Other income (expense), net	266	2,353
Income tax (expense)	(494)	(16,002)
Net income	100,487	97,224
Net income attributable to noncontrolling interest	(4,171)	(4,050)
Net income available for common stock	96,316	93,174
Inter-company Revenues
Segment Reporting Information
Revenue from contracts with customers	(39,848)	(38,642)
Revenues	(40,330)	(39,033)
Consolidation, Eliminations
Segment Reporting Information
Revenue from contracts with customers	0	0
Corporate
Segment Reporting Information
Operating income	(3,122)	160
Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	227,271	173,916
Revenues	227,408	174,139
Operating income	21,813	35,650
Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	400,019	355,065
Revenues	402,519	360,773
Operating income	102,094	102,897
Power Generation
Segment Reporting Information
Revenue from contracts with customers	28,692	25,467
Revenues	29,163	25,966
Operating income	14,269	11,349
Mining
Segment Reporting Information
Revenue from contracts with customers	14,083	14,403
Revenues	14,672	15,205
Operating income	3,261	3,129
Other Revenues
Segment Reporting Information
Revenues	3,215	6,841
Other Revenues | Inter-company Revenues
Segment Reporting Information
Revenues	(482)	(391)
Other Revenues | Consolidation, Eliminations
Segment Reporting Information
Revenues	0	0
Other Revenues | Electric Utilities
Segment Reporting Information
Revenues	137	223
Other Revenues | Gas Utilities
Segment Reporting Information
Revenues	2,500	5,708
Other Revenues | Power Generation
Segment Reporting Information
Revenues	471	499
Other Revenues | Mining
Segment Reporting Information
Revenues	589	802
External Operating Revenue
Segment Reporting Information
Revenue from contracts with customers	630,217	530,209
External Operating Revenue | Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	220,500	167,503
External Operating Revenue | Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	398,499	354,287
External Operating Revenue | Power Generation
Segment Reporting Information
Revenue from contracts with customers	4,241	1,855
External Operating Revenue | Mining
Segment Reporting Information
Revenue from contracts with customers	6,977	6,564
External Operating Revenue | Other Revenues
Segment Reporting Information
Revenues	3,215	6,841
External Operating Revenue | Other Revenues | Electric Utilities
Segment Reporting Information
Revenues	137	223
External Operating Revenue | Other Revenues | Gas Utilities
Segment Reporting Information
Revenues	2,408	5,708
External Operating Revenue | Other Revenues | Power Generation
Segment Reporting Information
Revenues	421	443
External Operating Revenue | Other Revenues | Mining
Segment Reporting Information
Revenues	249	467
Inter-company Operating Revenue | Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	6,771	6,413
Inter-company Operating Revenue | Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	1,520	778
Inter-company Operating Revenue | Power Generation
Segment Reporting Information
Revenue from contracts with customers	24,451	23,612
Inter-company Operating Revenue | Mining
Segment Reporting Information
Revenue from contracts with customers	7,106	7,839
Inter-company Operating Revenue | Other Revenues | Electric Utilities
Segment Reporting Information
Revenues	0	0
Inter-company Operating Revenue | Other Revenues | Gas Utilities
Segment Reporting Information
Revenues	92	0
Inter-company Operating Revenue | Other Revenues | Power Generation
Segment Reporting Information
Revenues	50	56
Inter-company Operating Revenue | Other Revenues | Mining
Segment Reporting Information
Revenues	$ 340	$ 335

Selected Balance Sheet Inform_3

Selected Balance Sheet Information: Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Selected Balance Sheet Information [Abstract]
Accounts receivable, trade	$ 199,548	$ 146,899
Unbilled revenue	91,085	126,065
Less: Allowance for doubtful accounts	(8,251)	(7,003)	$ (5,162)	$ (2,444)
Accounts receivable, net	$ 282,382	$ 265,961

Selected Balance Sheet Inform_4

Selected Balance Sheet Information: Changes to Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Selected Balance Sheet Information [Abstract]
Balance at Beginning of Year	$ 7,003	$ 2,444
Additions Charged to Costs and Expenses	1,877	3,519
Recoveries and Other Additions	1,014	922
Write-offs and Other Deductions	(1,643)	(1,723)
Balance at End of Year	$ 8,251	$ 5,162

Selected Balance Sheet Inform_5

Selected Balance Sheet Information: Materials and Supplies (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Selected Balance Sheet Information [Abstract]
Materials and supplies	$ 88,088	$ 85,250
Fuel - Electric Utilities	1,590	1,531
Natural gas in storage	12,925	30,619
Total materials, supplies and fuel	$ 102,603	$ 117,400

Selected Balance Sheet Inform_6

Selected Balance Sheet Information: Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Selected Balance Sheet Information [Abstract]
Accrued employee compensation, benefits and withholdings	$ 57,347	$ 77,806
Accrued property taxes	49,267	47,105
Customer deposits and prepayments	50,194	52,185
Accrued interest	45,896	31,520
Other (none of which is individually significant)	27,740	34,996
Total accrued liabilities	$ 230,444	$ 243,612