Black Hills (BKH) 10-Q 4 Aug 20 2020 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information Document - shares	6 Months Ended
	Jun. 30, 2020	Jul. 31, 2020
Document and Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
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		62,745,335
Entity Central Index Key	0001130464
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenues	$ 326,914	$ 333,888	$ 863,964	$ 931,698
Operating expenses:
Fuel, purchased power and cost of natural gas sold	71,629	90,200	259,508	339,942
Operations and maintenance	117,308	124,950	242,774	248,534
Depreciation, depletion and amortization	56,663	51,595	113,065	102,623
Taxes - property and production	14,381	13,142	28,499	26,467
Total operating expenses	259,981	279,887	643,846	717,566
Operating income	66,933	54,001	220,118	214,132
Other income (expense):
Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts)	(35,765)	(34,660)	(71,546)	(69,676)
Interest income	220	396	548	695
Impairment of investment	0	0	(6,859)	0
Other income (expense), net	(1,863)	263	490	(526)
Total other income (expense)	(37,408)	(34,001)	(77,367)	(69,507)
Income before income taxes	29,525	20,000	142,751	144,625
Income tax (expense)	(4,831)	(2,307)	(20,833)	(19,570)
Net income	24,694	17,693	121,918	125,055
Net income attributable to noncontrolling interest	(3,728)	(3,110)	(7,778)	(6,664)
Net income available for common stock	$ 20,966	$ 14,583	$ 114,140	$ 118,391
Earnings per share of common stock:
Earnings (loss) per share, Basic (usd per share)	$ 0.34	$ 0.24	$ 1.84	$ 1.97
Earnings (loss) per share, Diluted (usd per share)	$ 0.33	$ 0.24	$ 1.83	$ 1.96
Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract]
Basic (in shares)	62,573	60,467	62,175	60,195
Diluted (in shares)	62,617	60,606	62,230	60,333

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net income	$ 24,694	$ 17,693	$ 121,918	$ 125,055
Other comprehensive income (loss), net of tax:
Benefit plan liability adjustments - net gain (net of tax of $0,$0, $(17) and $0, respectively)	0	0	55	0
Reclassification adjustments of benefit plan liability - prior service cost (net of tax of $6, $5, $13 and $10, respectively)	(19)	(15)	(42)	(29)
Reclassification adjustments of benefit plan liability - net gain (net of tax of $(182), $(52), $(277) and $(105), respectively)	415	169	917	336
Other comprehensive income, net of tax	948	232	2,221	689
Comprehensive income	25,642	17,925	124,139	125,744
Net Income (Loss) Attributable to Noncontrolling Interest	3,728	3,110	7,778	6,664
Comprehensive income available for common stock	21,914	14,815	116,361	119,080
Benefit plan liability adjustments - net gain (loss) (tax) benefit	0	0	(17)	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, Tax	6	5	13	10
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	(182)	(52)	(277)	(105)
Interest rate swaps
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses	543	541	1,086	1,091
Reclassification of net realized gains/losses, (tax) benefit	(170)	(172)	(340)	(335)
Commodity Contract
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses	54	(64)	425	(490)
Net unrealized gains (losses) on commodity derivatives (net of tax of $14, $119, $68 and $65, respectively)	(45)	(399)	(220)	(219)
Reclassification of net realized gains/losses, (tax) benefit	(16)	19	(131)	147
Net unrealized gains/losses on commodity derivatives, (tax) benefit	$ 14	$ 119	$ 68	$ 65

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 31,608	$ 9,777
Restricted cash and equivalents	4,105	3,881
Accounts receivable, net	170,980	255,805
Materials, supplies and fuel	105,987	117,172
Derivative assets, current	1,581	342
Income tax receivable, net	20,118	16,446
Regulatory assets, current	51,745	43,282
Other current assets	27,981	26,479
Total current assets	414,105	473,184
Investments	15,438	21,929
Property, plant and equipment	6,954,274	6,784,679
Less: accumulated depreciation and depletion	(1,251,075)	(1,281,493)
Total property, plant and equipment, net	5,703,199	5,503,186
Other assets:
Goodwill	1,299,454	1,299,454
Intangible assets, net	12,536	13,266
Regulatory assets, non-current	220,567	228,062
Other assets, non-current	24,633	19,376
Total other assets, non-current	1,557,190	1,560,158
TOTAL ASSETS	7,689,932	7,558,457
Current liabilities:
Accounts payable	118,942	193,523
Accrued liabilities	201,667	226,767
Derivative liabilities, current	621	2,254
Regulatory liabilities, current	59,428	33,507
Notes payable	0	349,500
Current maturities of long-term debt	4,307	5,743
Total current liabilities	384,965	811,294
Long-term debt, net of current maturities	3,532,887	3,140,096
Deferred credits and other liabilities:
Deferred income tax liabilities, net	388,962	360,719
Regulatory liabilities, non-current	506,393	503,145
Benefit plan liabilities	142,580	154,472
Other deferred credits and other liabilities	119,649	124,662
Total deferred credits and other liabilities	1,157,584	1,142,998
Commitments and contingencies (See Notes 7, 9, 12, 13)
Equity:
Common stock $1 par value; 100,000,000 shares authorized; issued 62,772,996 and 61,480,658 shares, respectively	62,773	61,481
Additional paid-in capital	1,654,563	1,552,788
Retained earnings	826,269	778,776
Treasury stock, at cost – 26,399 and 3,956 shares, respectively	(1,879)	(267)
Accumulated other comprehensive income (loss)	(28,434)	(30,655)
Total stockholders’ equity	2,513,292	2,362,123
Noncontrolling interest	101,204	101,946
Total equity	2,614,496	2,464,069
TOTAL LIABILITIES AND TOTAL EQUITY	$ 7,689,932	$ 7,558,457
Common Stock, Par Value (usd per share)	$ 1	$ 1
Common Stock Authorized (in shares)	100,000,000	100,000,000
Common Stock Issued (in shares)	62,772,996	61,480,658
Treasury Stock (in shares)	26,399	3,956

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities:
Net income	$ 121,918	$ 125,055
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	113,065	102,623
Deferred financing cost amortization	4,246	4,219
Impairment of investment	6,859	0
Stock compensation	1,113	7,093
Deferred income taxes	26,401	21,935
Employee benefit plans	5,656	5,683
Other adjustments, net	3,679	8,991
Changes in certain operating assets and liabilities:
Materials, supplies and fuel	7,503	14,911
Accounts receivable and other current assets	73,302	99,925
Accounts payable and other current liabilities	(63,085)	(107,563)
Regulatory assets - current	21,887	16,116
Regulatory liabilities - current	314	(6,348)
Payment for Pension Benefits	(12,700)	0
Other operating activities, net	(1,152)	(2,861)
Net cash provided by operating activities	309,006	289,779
Investing activities:
Property, plant and equipment additions	(348,313)	(317,686)
Other investing activities	(1,412)	389
Net cash (used in) investing activities	(349,725)	(317,297)
Financing activities:
Dividends paid on common stock	(66,440)	(60,952)
Common stock issued	99,435	71,759
Net (payments) borrowings of short-term debt	(349,500)	(83,120)
Long-term debt - issuances	400,000	400,000
Long-term debt - repayments	(5,727)	(302,871)
Distributions to noncontrolling interest	(8,520)	(9,251)
Other financing activities	(6,474)	(1,948)
Net cash provided by financing activities	62,774	13,617
Net change in cash, restricted cash and cash equivalents	22,055	(13,901)
Cash, restricted cash and cash equivalents at beginning of period	13,658	24,145
Cash, restricted cash and cash equivalents at end of period	35,713	10,244
Supplemental Cash Flow Information [Abstract]
Interest (net of amounts capitalized)	(67,449)	(67,624)
Income taxes	1,896	1,790
Accrued property, plant and equipment purchases at June 30	$ 59,916	$ 83,486

Condensed Consolidated Statem_4

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	Accumulated Other Comprehensive Income (loss)	Noncontrolling Interest
Common Stock, Shares, Outstanding at Dec. 31, 2018			60,048,567	44,253
Total equity at Dec. 31, 2018	$ 2,287,423		$ 60,049	$ (2,510)	$ 1,450,569	$ 700,396	$ (26,916)	$ 105,835
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	107,362					103,808		3,554
Other comprehensive income (loss), net of tax	457						457
Dividends on Common Stock	(30,332)					(30,332)
Share-based compensation, shares			48,956	(20,497)
Share-based compensation	538		$ 49	$ 1,078	(589)
Issuance of common stock, shares			280,497
Issuance of common stock	19,999		$ 280		19,719
Issuance costs	(289)				(289)
Distributions to noncontrolling interest	(4,846)							(4,846)
Common Stock, Shares, Outstanding at Mar. 31, 2019			60,378,020	23,756
Total equity at Mar. 31, 2019	$ 2,383,702	$ 3,390	$ 60,378	$ (1,432)	1,469,410	777,262	(26,459)	104,543
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.505
Common Stock, Shares, Outstanding at Dec. 31, 2018			60,048,567	44,253
Total equity at Dec. 31, 2018	$ 2,287,423		$ 60,049	$ (2,510)	1,450,569	700,396	(26,916)	105,835
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	125,055
Other comprehensive income (loss), net of tax	689
Issuance costs			$ (700)
Common Stock, Shares, Outstanding at Jun. 30, 2019			61,091,385	25,359
Total equity at Jun. 30, 2019	2,419,998	(3)	$ 61,091	$ (1,544)	1,522,208	761,222	(26,227)	103,248
Common Stock, Shares, Outstanding at Mar. 31, 2019			60,378,020	23,756
Total equity at Mar. 31, 2019	2,383,702	3,390	$ 60,378	$ (1,432)	1,469,410	777,262	(26,459)	104,543
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	17,693					14,583		3,110
Other comprehensive income (loss), net of tax	232						232
Dividends on Common Stock	(30,620)					(30,620)
Share-based compensation, shares			54,767	1,603
Share-based compensation	3,890		$ 54	$ (112)	3,948
Issuance of common stock, shares			658,598
Issuance of common stock	50,001		$ 659		49,342
Issuance costs	(492)		$ (500)		(492)
Distributions to noncontrolling interest	(4,405)							(4,405)
Common Stock, Shares, Outstanding at Jun. 30, 2019			61,091,385	25,359
Total equity at Jun. 30, 2019	$ 2,419,998	(3)	$ 61,091	$ (1,544)	1,522,208	761,222	(26,227)	103,248
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.505
Common Stock, Shares, Outstanding at Dec. 31, 2019			61,480,658	3,956
Total equity at Dec. 31, 2019	$ 2,464,069		$ 61,481	$ (267)	1,552,788	778,776	(30,655)	101,946
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	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, shares			69,378	20,700
Share-based compensation	674		$ 69	$ (1,658)	2,263
Issuance of common stock, 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)
Common Stock, Shares, Outstanding at Mar. 31, 2020			62,772,978	24,656
Total equity at Mar. 31, 2020	$ 2,624,423	(207)	$ 62,773	$ (1,925)	1,652,861	838,841	(29,382)	101,255
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.535
Common Stock, Shares, Outstanding at Dec. 31, 2019			61,480,658	3,956
Total equity at Dec. 31, 2019	$ 2,464,069		$ 61,481	$ (267)	1,552,788	778,776	(30,655)	101,946
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	121,918
Other comprehensive income (loss), net of tax	2,221
Common Stock, Shares, Outstanding at Jun. 30, 2020			62,772,996	26,399
Total equity at Jun. 30, 2020	2,614,496		$ 62,773	$ (1,879)	1,654,563	826,269	(28,434)	101,204
Common Stock, Shares, Outstanding at Mar. 31, 2020			62,772,978	24,656
Total equity at Mar. 31, 2020	2,624,423	$ (207)	$ 62,773	$ (1,925)	1,652,861	838,841	(29,382)	101,255
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	24,694					20,966		3,728
Other comprehensive income (loss), net of tax	948						948
Dividends on Common Stock	(33,538)					(33,538)
Share-based compensation, shares			18	1,743
Share-based compensation	1,827			$ 46	1,781
Issuance costs	(79)				(79)
Distributions to noncontrolling interest	(3,779)							(3,779)
Common Stock, Shares, Outstanding at Jun. 30, 2020			62,772,996	26,399
Total equity at Jun. 30, 2020	$ 2,614,496		$ 62,773	$ (1,879)	$ 1,654,563	$ 826,269	$ (28,434)	$ 101,204
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.535

Management's Statement_

Management's Statement:	6 Months Ended
	Jun. 30, 2020
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 GAAP 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 2019 Annual Report on Form 10-K filed with the SEC. 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 June 30, 2020, December 31, 2019 and June 30, 2019 financial information. Certain industries in which we operate are highly seasonal and revenue from, and certain expenses for, such operations may fluctuate significantly among quarterly periods. Demand for electricity and natural gas is sensitive to seasonal cooling, heating and industrial load requirements. In particular, the normal peak usage season for electric utilities is June through August while the normal peak usage season for gas utilities is November through March. Significant earnings variances can be expected between the Gas Utilities segment’s peak and off-peak seasons. Due to this seasonal nature, our results of operations for the three and six months ended June 30, 2020 and June 30, 2019, and our financial condition as of June 30, 2020 and December 31, 2019 are not necessarily indicative of the results of operations and financial condition to be expected for any other period. All earnings per share amounts discussed refer to diluted earnings per share unless otherwise noted. Reclassification We changed certain classifications of operating expenses on the Condensed Consolidated Statements of Income for the three and six months ended June 30, 2019 to conform with current year presentation. The prior year reclassifications, which are shown in the table below, did not impact previously reported operating income or net income. Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 (in millions) Fuel, purchased power and cost of natural gas sold $ 0.4 $ 1.3 Operations and maintenance — (0.3) Taxes - property and production — (0.2) Other operating expenses (0.4) (0.8) $ — $ — 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 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 its employees and the communities in which it operates while assuring the continuity of its business operations. The Company’s Condensed Consolidated Financial Statements reflect estimates and assumptions made by management that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the Condensed Consolidated Financial Statements and reported amounts of revenue and expenses during the reporting periods presented. The Company considered the impacts of COVID-19 on the assumptions and estimates used and determined that for the three and six months ended June 30, 2020, there were no material adverse impacts on the Company’s results of operations. Change in Accounting Principle - Pension Accounting Asset Method Effective January 1, 2020, we changed our method of accounting for net periodic benefit cost. Prior to the change, the Company used a calculated value for determining market-related value of plan assets which amortized the effects of gains and losses over a five-year period. Effective with the accounting change, the Company will use a calculated value for the return-seeking assets (equities) in the portfolio and change to fair value for the liability-hedging assets (fixed income). See Note 12 for additional information. Recently Issued 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. The new guidance is effective for interim and annual periods beginning after December 15, 2020 with early adoption permitted. We are currently reviewing this standard to assess the impact on our financial position, results of operations and cash flows. Recently Adopted Accounting Standards Financial Instruments -- Credit Losses: Measurement of Credit Losses on Financial Instruments, ASU 2016-13 In June 2016, the FASB issued ASU 2016-13, Financial Instruments -- Credit Losses: Measurement of Credit Losses on Financial Instruments, which was subsequently amended by ASUs 2018-19, 2019-04, 2019-05, 2019-10, and 2019-11. The standard introduces new accounting guidance for credit losses on financial instruments within its scope, including trade receivables. This new guidance adds an impairment model that is based on expected losses rather than incurred losses. We adopted this standard on January 1, 2020 with prior year comparative financial information remaining as previously reported when transitioning to the new standard. On January 1, 2020, we recorded an increase to our allowance for credit losses, primarily associated with the inclusion of expected losses on unbilled revenue. The cumulative effect of the adoption, net of tax impact, was $0.2 million, which was recorded as an adjustment to retained earnings. Simplifying the Test for Goodwill Impairment, ASU 2017-04 In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment, by eliminating step 2 from the goodwill impairment test. Under the new guidance, if the carrying amount of a reporting unit exceeds its fair value, an impairment loss will be recognized in an amount equal to that excess, limited to the amount of goodwill allocated to that reporting unit. We adopted this standard prospectively on January 1, 2020. Adoption of this guidance, in conjunction with the annual goodwill impairment test as of October 1, 2020, is not expected to have an impact on our financial position, results of operations or cash flows. Internal-Use Software: Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, ASU 2018-15 In August 2018, the FASB issued ASU 2018-15, Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract , which aligns the requirements for recording implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. As a result, certain categories of implementation costs that previously would have been charged to expense as incurred are now capitalized as prepayments and amortized over the term of the arrangement. We adopted this standard prospectively on January 1, 2020. Adoption of this guidance did not have a material impact on our financial position, results of operations or cash flows.

Revenue

Revenue	6 Months Ended
	Jun. 30, 2020
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 reporting segments for the three and six months ended June 30, 2020 and 2019. Sales tax and other similar taxes are excluded from revenues. Three Months Ended June 30, 2020 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 141,804 $ 120,594 $ — $ 14,846 $ (7,916) $ 269,328 Transportation — 30,792 — — (138) 30,654 Wholesale 3,470 — 25,718 — (24,476) 4,712 Market - off-system sales 3,538 23 — — (1,580) 1,981 Transmission/Other 12,761 9,189 — — (4,432) 17,518 Revenue from contracts with customers $ 161,573 $ 160,598 $ 25,718 $ 14,846 $ (38,542) $ 324,193 Other revenues 1,627 512 404 570 (392) 2,721 Total revenues $ 163,200 $ 161,110 $ 26,122 $ 15,416 $ (38,934) $ 326,914 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 14,846 $ (7,916) $ 6,930 Services transferred over time 161,573 160,598 25,718 — (30,626) 317,263 Revenue from contracts with customers $ 161,573 $ 160,598 $ 25,718 $ 14,846 $ (38,542) $ 324,193 Three Months Ended June 30, 2019 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer Types: Retail $ 139,732 $ 123,630 $ — $ 12,428 $ (7,041) $ 268,749 Transportation — 28,623 — — (276) 28,347 Wholesale 6,781 — 15,062 — (13,296) 8,547 Market - off-system sales 3,448 161 — — (1,335) 2,274 Transmission/Other 14,416 11,612 — — (4,199) 21,829 Revenue from contracts with customers $ 164,377 $ 164,026 $ 15,062 $ 12,428 $ (26,147) $ 329,746 Other revenues 1,977 1,443 9,646 617 (9,541) 4,142 Total Revenues $ 166,354 $ 165,469 $ 24,708 $ 13,045 $ (35,688) $ 333,888 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 12,428 $ (7,041) $ 5,387 Services transferred over time 164,377 164,026 15,062 — (19,106) 324,359 Revenue from contracts with customers $ 164,377 $ 164,026 $ 15,062 $ 12,428 $ (26,147) $ 329,746 Six Months Ended June 30, 2020 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 290,444 $ 418,841 $ — $ 29,249 $ (15,755) $ 722,779 Transportation — 74,900 — — (277) 74,623 Wholesale 9,022 — 51,185 — (48,088) 12,119 Market - off-system sales 8,405 161 — — (4,219) 4,347 Transmission/Other 27,618 21,761 — — (8,845) 40,534 Revenue from contracts with customers $ 335,489 $ 515,663 $ 51,185 $ 29,249 $ (77,184) $ 854,402 Other revenues 1,850 6,220 903 1,372 (783) 9,562 Total revenues $ 337,339 $ 521,883 $ 52,088 $ 30,621 $ (77,967) $ 863,964 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 29,249 $ (15,755) $ 13,494 Services transferred over time 335,489 515,663 51,185 — (61,429) 840,908 Revenue from contracts with customers $ 335,489 $ 515,663 $ 51,185 $ 29,249 $ (77,184) $ 854,402 Six Months Ended June 30, 2019 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer Types: Retail $ 293,195 $ 477,905 $ — $ 28,257 $ (15,169) $ 784,188 Transportation — 73,140 — — (708) 72,432 Wholesale 15,124 — 30,531 — (26,509) 19,146 Market - off-system sales 10,140 378 — — (3,559) 6,959 Transmission/Other 28,591 24,802 — — (8,402) 44,991 Revenue from contracts with customers $ 347,050 $ 576,225 $ 30,531 $ 28,257 $ (54,347) $ 927,716 Other revenues 2,231 324 19,422 1,217 (19,212) 3,982 Total Revenues $ 349,281 $ 576,549 $ 49,953 $ 29,474 $ (73,559) $ 931,698 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 28,257 $ (15,169) $ 13,088 Services transferred over time 347,050 576,225 30,531 — (39,178) 914,628 Revenue from contracts with customers $ 347,050 $ 576,225 $ 30,531 $ 28,257 $ (54,347) $ 927,716 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 4 .

Business Segment Information_

Business Segment Information:	6 Months Ended
	Jun. 30, 2020
Segment Reporting Information, Additional Information [Abstract]
Business Segment Information	Business Segment Information Our reportable segments are based on our method of internal reporting, which is generally segregated by differences in products, services and regulation. All of our operations and assets are located within the United States. Segment and Corporate and Other information is as follows (in thousands): Three Months Ended June 30, 2020 External Operating Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 156,197 $ 1,627 $ 5,376 $ — $ 163,200 Gas Utilities 159,824 512 774 — 161,110 Power Generation 1,242 349 24,476 55 26,122 Mining 6,930 233 7,916 337 15,416 Inter-company eliminations — — (38,542) (392) (38,934) Total $ 324,193 $ 2,721 $ — $ — $ 326,914 Three Months Ended June 30, 2019 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 159,140 $ 1,977 $ 5,237 $ — $ 166,354 Gas Utilities 163,303 1,443 723 — 165,469 Power Generation 1,765 434 13,297 9,212 24,708 Mining 5,538 288 6,890 329 13,045 Inter-company eliminations — — (26,147) (9,541) (35,688) Total $ 329,746 $ 4,142 $ — $ — $ 333,888 Six Months Ended June 30, 2020 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 323,700 $ 1,850 $ 11,789 $ — $ 337,339 Gas Utilities 514,111 6,220 1,552 — 521,883 Power Generation 3,097 792 48,088 111 52,088 Mining 13,494 700 15,755 672 30,621 Inter-company eliminations — — (77,184) (783) (77,967) Total $ 854,402 $ 9,562 $ — $ — $ 863,964 Six Months Ended June 30, 2019 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 335,803 $ 2,231 $ 11,247 $ — $ 349,281 Gas Utilities 574,803 324 1,422 — 576,549 Power Generation 4,022 870 26,509 18,552 49,953 Mining 13,088 557 15,169 660 29,474 Inter-company eliminations — — (54,347) (19,212) (73,559) Total $ 927,716 $ 3,982 $ — $ — $ 931,698 Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Adjusted operating income (a) : Electric Utilities $ 33,993 $ 33,546 $ 69,643 $ 74,566 Gas Utilities 18,209 8,557 121,106 111,871 Power Generation 11,402 10,156 22,751 22,123 Mining 3,358 1,640 6,487 5,977 Corporate and Other (29) 102 131 (405) Operating income 66,933 54,001 220,118 214,132 Interest expense, net (35,545) (34,264) (70,998) (68,981) Impairment of investment — — (6,859) — Other income (expense), net (1,863) 263 490 (526) Income tax (expense) (4,831) (2,307) (20,833) (19,570) Net income 24,694 17,693 121,918 125,055 Net income attributable to noncontrolling interest (3,728) (3,110) (7,778) (6,664) Net income available for common stock $ 20,966 $ 14,583 $ 114,140 $ 118,391 __________ (a) Adjusted operating income recognizes intersegment revenues and costs for Colorado Electric’s PPA with Black Hills Colorado IPP on an accrual basis rather than as a finance lease. This presentation of segment information does not impact consolidated financial results. Segment and Corporate and Other balances included in the accompanying Condensed Consolidated Balance Sheets were as follows (in thousands): Total assets (net of inter-company eliminations) as of: June 30, 2020 December 31, 2019 Segment: Electric Utilities $ 2,982,841 $ 2,900,983 Gas Utilities 4,052,860 4,032,339 Power Generation 407,107 417,715 Mining 79,774 77,175 Corporate and Other 167,350 130,245 Total assets $ 7,689,932 $ 7,558,457

Selected Balance Sheet Informat

Selected Balance Sheet Information:	6 Months Ended
	Jun. 30, 2020
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: June 30, 2020 December 31, 2019 Accounts receivable, trade $ 122,650 $ 144,747 Unbilled revenue 55,915 113,502 Less: Allowance for credit losses (7,585) (2,444) Accounts receivable, net $ 170,980 $ 255,805 Changes to allowance for credit losses for the six months ended June 30, 2020 and 2019, 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 June 30, 2020 $ 2,444 $ 6,715 $ 2,203 $ (3,777) $ 7,585 2019 $ 3,209 $ 4,913 $ 1,870 $ (4,906) $ 5,086 Due to the COVID-19 pandemic, all of our jurisdictions temporarily suspended disconnections for a period of time, which increased our accounts receivable arrears balances. As a result, we increased our allowance for credit losses and bad debt expense for the six months ended June 30, 2020 by $2.0 million. The ongoing credit evaluation of our customers during the COVID-19 pandemic is further discussed in the Credit Risk section of Note 9 . 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: June 30, 2020 December 31, 2019 Materials and supplies $ 92,284 $ 82,809 Fuel - Electric Utilities 3,574 2,425 Natural gas in storage 10,129 31,938 Total materials, supplies and fuel $ 105,987 $ 117,172 Accrued Liabilities The following amounts by major classification are included in Accrued liabilities on the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: June 30, 2020 December 31, 2019 Accrued employee compensation, benefits and withholdings $ 59,701 $ 62,837 Accrued property taxes 36,832 44,547 Customer deposits and prepayments 45,143 54,728 Accrued interest 31,757 31,868 Other (none of which is individually significant) 28,234 32,787 Total accrued liabilities $ 201,667 $ 226,767

Regulatory Matters_

Regulatory Matters:	6 Months Ended
	Jun. 30, 2020
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Matters	Regulatory Matters We had the following regulatory assets and liabilities (in thousands) as of: June 30, 2020 December 31, 2019 Regulatory assets Deferred energy and fuel cost adjustments (a) $ 36,900 $ 34,088 Deferred gas cost adjustments (a) 226 1,540 Gas price derivatives (a) 662 3,328 Deferred taxes on AFUDC (b) 7,715 7,790 Employee benefit plans (c) 115,416 115,900 Environmental (a) 1,426 1,454 Loss on reacquired debt (a) 23,820 24,777 Renewable energy standard adjustment (a) 1 1,622 Deferred taxes on flow through accounting (c) 44,940 41,220 Decommissioning costs (b) 9,854 10,670 Gas supply contract termination (a) 5,521 8,485 Other regulatory assets (a) 25,831 20,470 Total regulatory assets 272,312 271,344 Less current regulatory assets (51,745) (43,282) Regulatory assets, non-current $ 220,567 $ 228,062 Regulatory liabilities Deferred energy and gas costs (a) $ 28,279 $ 17,278 Employee benefit plan costs and related deferred taxes (c) 41,025 43,349 Cost of removal (a) 168,137 166,727 Excess deferred income taxes (c) 288,796 285,438 TCJA revenue reserve 3,027 3,418 Other regulatory liabilities (c) 36,557 20,442 Total regulatory liabilities 565,821 536,652 Less current regulatory liabilities (59,428) (33,507) Regulatory liabilities, non-current $ 506,393 $ 503,145 __________ (a) Recovery of costs, but we are not allowed a rate of return. (b) In addition to recovery of costs, we are allowed a rate of return. (c) 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 13 of the Notes to the Consolidated Financial Statements in our 2019 Annual Report on Form 10-K. Nebraska Gas Jurisdictional Consolidation and Rate Review On June 1, 2020, Nebraska Gas filed a rate review with the NPSC to consolidate rates, tariffs, and services of its two existing gas distribution territories. The rate review requests $17 million in new revenue, as well as renewal and expansion of the SSIR, to recover investments in safety, reliability and system integrity. The rate review requests a capital structure of 50% equity and 50% debt and a return on equity of 10% for investments Nebraska Gas made in its natural gas pipeline system. Nebraska statute allows for implementation of interim rates 90 days after filing a rate review. New rates are expected to be effective in early 2021. Black Hills Wyoming and Wyoming Electric Wygen I FERC Filing On June 1, 2020, Black Hills Wyoming and Wyoming Electric filed a settlement agreement with the FERC. The agreement represents a resolution of all issues in the joint application filed with the FERC on August 2, 2019 for approval of a new 60 MW PPA. On July 10, 2020, a judge certified the settlement to the FERC and a decision is expected by the end of 2020. If approved, Wyoming Electric will continue to receive 60 MW of capacity and energy from the Wygen I power plant. The new agreement would commence on January 1, 2022, replacing the existing PPA, and would continue for 11 years. Colorado Gas Jurisdictional Consolidation and Rate Review On February 1, 2019, Colorado Gas filed a rate review with the CPUC requesting $2.5 million in new revenue to recover investments in safety, reliability and system integrity and approval to consolidate rates, tariffs, and services of its two existing gas distribution territories. Colorado Gas also requested a new rider mechanism to recover future safety and integrity investments in its system. On April 14, 2020 the CPUC deliberated on the application and on May 19, 2020 issued a final order. The order denied the system integrity recovery mechanism and consolidation of rate territories. In addition, the order resulted in an annual revenue decrease of $0.6 million and a return on equity of 9.2%. New rates were effective July 3, 2020. In accordance with the final order, Colorado Gas will file a new system integrity rider proposal prior to the end of 2020. Colorado Gas also plans to file a new rate review by the end of 2020.

Earnings Per Share_

Earnings Per Share:	6 Months Ended
	Jun. 30, 2020
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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Net income available for common stock $ 20,966 $ 14,583 $ 114,140 $ 118,391 Weighted average shares - basic 62,573 60,467 62,175 60,195 Dilutive effect of: Equity compensation 44 139 55 138 Weighted average shares - diluted 62,617 60,606 62,230 60,333 Earnings per share of common stock: Earnings per share, Basic $ 0.34 $ 0.24 $ 1.84 $ 1.97 Earnings per share, Diluted $ 0.33 $ 0.24 $ 1.83 $ 1.96 The following securities were excluded from the diluted earnings per share computation because of their anti-dilutive nature (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Equity compensation 29 — 26 — Restricted stock 76 — 36 — Anti-dilutive shares 105 — 62 —

Notes Payable, Current Maturiti

Notes Payable, Current Maturities and Debt:	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Notes Payable, Current Maturities and Debt	Notes Payable, Current Maturities and Debt We had the following short-term debt outstanding in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: June 30, 2020 December 31, 2019 Balance Outstanding Letters of Credit (a) Balance Outstanding Letters of Credit (a) Revolving Credit Facility $ — $ 11,999 $ — $ 30,274 CP Program — — 349,500 — Total $ — $ 11,999 $ 349,500 $ 30,274 _______________ (a) Letters of credit are off-balance sheet commitments that reduce the borrowing capacity available on our corporate Revolving Credit Facility. For the six months ended June 30, 2020, we utilized a combination of our $750 million Revolving Credit Facility and CP Program to meet our business needs and support our capital investment plan. Our net short-term borrowings (payments) during the six months ended June 30, 2020 were $(350) million. Debt Covenants Under our Revolving Credit Facility and term loan agreement, 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 June 30, 2020: As of June 30, 2020 Covenant Requirement Consolidated Indebtedness to Capitalization Ratio 58.7% Less than 65% Debt Offering On June 17, 2020, we completed a public debt offering which consisted of $400 million of 2.50% 10-year senior unsecured notes due June 15, 2030. The proceeds were used to repay short-term debt and for working capital and general corporate purposes. South Dakota Electric Series 94A Debt On March 24, 2020, South Dakota Electric paid off its $2.9 million, Series 94A variable rate notes due June 1, 2024. These notes were tendered by the sole investor on March 17, 2020.

Equity_

Equity:	6 Months Ended
	Jun. 30, 2020
Statement of Stockholders' Equity [Abstract]
Equity	Equity February 2020 Equity Issuance On February 27, 2020, we issued 1.2 million shares of common stock to a single investor through an underwritten registered transaction at a price of $81.77 per share for proceeds of $99 million, net of $1.0 million of issuance costs. The shares of common stock were offered pursuant to our shelf registration statement filed with the SEC. Shelf Registration, DRSPP and ATM Activity On August 3, 2020, we filed a shelf registration and DRSPP with the SEC. In conjunction with these shelf filings, we renewed the ATM. The renewed ATM program, which allows us to sell shares of our common stock, is the same as the prior program other than the aggregate value increased from $300 million to $400 million and a forward sales option was incorporated. Under the ATM, shares may be offered from time to time pursuant to a sales agreement dated August 3, 2020. Shares of common stock are offered pursuant to our shelf registration statement filed with the SEC. We did not issue any common shares under the ATM during the three and six months ended June 30, 2020. During the three months ended June 30, 2019, we issued a total of 0.7 million shares of common stock under the ATM for proceeds of $49 million, net of $0.5 million in issuance costs. During the six months ended June 30, 2019, we issued a total of 0.9 million shares of common stock under the ATM for proceeds of $69 million, net of $0.7 million in issuance costs.

Risk Management and Derivatives

Risk Management and Derivatives:	6 Months Ended
	Jun. 30, 2020
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, wholesale electric power marketing activities and our fuel procurement for several of our gas-fired generation assets which include market fluctuations due to unpredictable factors such as the COVID-19 pandemic, weather, market speculation, pipeline constraints, and other factors that may impact natural gas and electric energy supply and demand; • 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. For production and generation activities, 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 on payment history and the customers’ current creditworthiness, as determined by review of their current credit information. We maintain a provision for estimated credit losses based upon historical experience, changes in current market conditions, expected losses and any specific customer collection issue that is identified. We continue to monitor COVID-19 impacts and changes to customer load, consistency in customer payments, requests for deferred or discounted payments, and requests for changes to credit limits to quantify estimated future financial impacts to the allowance for credit losses. During the three and six months ended June 30, 2020, the potential economic impact of the COVID-19 pandemic was considered in forward looking projections related to write-off and recovery rates, and resulted in increases to the allowance for credit losses and bad debt expense of $1.5 million and $2.0 million, respectively. See Note 4 for further information. 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 10 . Utilities The operations of our utilities, including natural gas used by our Electric Utilities’ generation plants or those plants under PPAs where our Electric Utilities must provide the generation fuel (tolling agreements) and natural gas sold by our Gas Utilities, expose our utility customers to volatility in natural gas prices. Therefore, as allowed or required by state utility 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 utility commission guidelines. When the related costs are recovered through our rates, the hedging activity is 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/or sales from July 2020 through May 2022. 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 effective portion of the gain or loss on these designated derivatives is reported in AOCI in the accompanying Condensed Consolidated Balance Sheets and the ineffective portion, if any, is reported in Fuel, purchased power and cost of natural gas sold. 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: June 30, 2020 December 31, 2019 Units Notional Maximum Term (months) (a) Notional Maximum Term (months) (a) Natural gas futures purchased MMBtus 660,000 9 1,450,000 12 Natural gas options purchased, net MMBtus 950,000 9 3,240,000 3 Natural gas basis swaps purchased MMBtus 520,000 6 1,290,000 12 Natural gas over-the-counter swaps, net (b) MMBtus 6,480,000 23 4,600,000 24 Natural gas physical contracts, net (c) MMBtus 8,085,376 9 13,548,235 12 Electric wholesale contracts (c) MWh 141,225 6 — 0 __________ (a) Term reflects the maximum forward period hedged. (b) As of June 30, 2020, 1,776,900 MMBtus of natural gas over-the-counter swaps purchases were designated as cash flow hedges. (c) Volumes exclude contracts that qualify for the normal purchases and normal sales exception. 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 June 30, 2020, the Company posted $0.5 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 June 30, 2020 December 31, 2019 Derivatives designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 66 $ 1 Noncurrent commodity derivatives Other assets, non-current 83 3 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current (324) (490) Noncurrent commodity derivatives Other deferred credits and other liabilities — (29) Total derivatives designated as hedges $ (175) $ (515) Derivatives not designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 1,515 $ 341 Noncurrent commodity derivatives Other assets, non-current 191 2 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current (297) (1,764) Noncurrent commodity derivatives Other deferred credits and other liabilities (15) (63) Total derivatives not designated as hedges $ 1,394 $ (1,484) Derivatives Designated as Hedges The impacts of cash flow hedges on our Condensed Consolidated Statements of Comprehensive Income and Condensed Consolidated Statements of Income are presented below for the three and six months ended June 30, 2020 and 2019. 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 June 30, Three Months Ended June 30, 2020 2019 2020 2019 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 11 (601) Fuel, purchased power and cost of natural gas sold (70) 83 Total $ 724 $ 112 $ (783) $ (630) Six Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 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 $ 1,426 $ 1,426 Interest expense $ (1,426) $ (1,426) Commodity derivatives 268 (921) Fuel, purchased power and cost of natural gas sold (556) 637 Total $ 1,694 $ 505 $ (1,982) $ (789) Based on June 30, 2020 prices, a $0.2 million gain would be realized, reported in pre-tax earnings and reclassified from AOCI during the next 12 months. As market prices fluctuate, estimated and actual realized gains or losses will change during future periods. Derivatives Not Designated as Hedges The following table summarizes the impacts of derivative instruments not designated as hedge instruments on our Condensed Consolidated Statements of Income for the three and six months ended June 30, 2020 and 2019. 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 June 30, 2020 2019 Derivatives Not Designated as Hedging Instruments Income Statement Location Amount of Gain/(Loss) on Derivatives Recognized in Income Commodity derivatives - Electric Fuel, purchased power and cost of natural gas sold $ (204) $ — Commodity derivatives - Natural Gas Fuel, purchased power and cost of natural gas sold 449 (1,185) $ 245 $ (1,185) Six Months Ended June 30, 2020 2019 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 $ 1,158 $ — Commodity derivatives - Natural Gas Fuel, purchased power and cost of natural gas sold 1,215 (1,160) $ 2,373 $ (1,160) As discussed above, financial instruments used in our regulated utilities are not designated as cash flow hedges. There is no earnings impact for our Gas Utilities 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 accounts related to the hedges in our Gas Utilities were $0.7 million and $3.3 million as of June 30, 2020 and December 31, 2019, 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:	6 Months Ended
	Jun. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	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; and 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 to the Consolidated Financial Statements included in our 2019 Annual Report on Form 10-K filed with the SEC. As of June 30, 2020 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Total (in thousands) Assets: Commodity derivatives — Gas Utilities $ — $ 1,114 $ — $ (417) $ 697 Commodity derivatives — Electric Utilities — 1,158 — — 1,158 Total $ — $ 2,272 $ — $ (417) $ 1,855 Liabilities: Commodity derivatives — Gas Utilities $ — $ 1,553 $ — $ (917) $ 636 Total $ — $ 1,553 $ — $ (917) $ 636 As of December 31, 2019 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Total (in thousands) Assets: Commodity derivatives — Gas Utilities $ — $ 1,433 $ — $ (1,085) $ 348 Total $ — $ 1,433 $ — $ (1,085) $ 348 Liabilities: Commodity derivatives — Gas Utilities $ — $ 5,254 $ — $ (2,909) $ 2,345 Total $ — $ 5,254 $ — $ (2,909) $ 2,345 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 18 to the Consolidated Financial Statements included in our 2019 Annual Report on Form 10-K. The Company has concluded that the market volatility associated with COVID-19 does not require interim re-measurement of our pension plan assets or defined benefit obligations. See Note 12 for additional information. Nonrecurring Fair Value Measurement A discussion of the fair value of our investment in equity securities of a privately held oil and gas company, a Level 3 asset, is included in Note 15 . Other Fair Value Measures 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: June 30, 2020 December 31, 2019 Carrying Fair Value Carrying Fair Value Long-term debt, including current maturities (a) $ 3,537,194 $ 4,051,912 $ 3,145,839 $ 3,479,367 __________ (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 (Los

Other Comprehensive Income (Loss):	6 Months Ended
	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) 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 Six Months Ended June 30, 2020 2019 2020 2019 Gains and (losses) on cash flow hedges: Interest rate swaps Interest expense $ (713) $ (713) $ (1,426) $ (1,426) Commodity contracts Fuel, purchased power and cost of natural gas sold (70) 83 (556) 637 (783) (630) (1,982) (789) Income tax Income tax benefit (expense) 186 153 471 188 Total reclassification adjustments related to cash flow hedges, net of tax $ (597) $ (477) $ (1,511) $ (601) Amortization of components of defined benefit plans: Prior service cost Operations and maintenance $ 25 $ 20 $ 55 $ 39 Actuarial gain (loss) Operations and maintenance (597) (221) (1,194) (441) (572) (201) (1,139) (402) Income tax Income tax benefit (expense) 176 47 264 95 Total reclassification adjustments related to defined benefit plans, net of tax $ (396) $ (154) $ (875) $ (307) Total reclassifications $ (993) $ (631) $ (2,386) $ (908) Balances by classification included within AOCI, net of tax on the accompanying Condensed Consolidated Balance Sheets were as follows (in thousands): 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 — (220) 55 (165) Amounts reclassified from AOCI 1,087 424 875 2,386 As of June 30, 2020 $ (14,035) $ (252) $ (14,147) $ (28,434) Interest Rate Swaps Commodity Derivatives Employee Benefit Plans Total As of December 31, 2018 $ (17,307) $ 328 $ (9,937) $ (26,916) Other comprehensive income (loss) before reclassifications — (219) — (219) Amounts reclassified from AOCI 1,091 (490) 307 908 As of June 30, 2019 $ (16,216) $ (381) $ (9,630) $ (26,227)

Employee Benefit Plans_

Employee Benefit Plans:	6 Months Ended
	Jun. 30, 2020
Defined Benefit Plan [Abstract]
Employee Benefit Plans	Employee Benefit Plans Change in Accounting Principle - Pension Accounting Asset Method Effective January 1, 2020, the Company changed its method of accounting for net periodic benefit cost. Prior to the change, the Company used a calculated value for determining market-related value of plan assets which amortized the effects of gains and losses over a five-year period. Effective with the accounting change, the Company will use a calculated value for the return-seeking assets (equities) in the portfolio and fair value for the liability-hedging assets (fixed income). The Company considers the fair value method for determining market-related value of liability-hedging assets to be a preferable method of accounting because asset-related gains and losses are subject to amortization into pension cost immediately. Additionally, the fair value for liability-hedging assets allows for the impact of gains and losses on this portion of the asset portfolio to be reflected in tandem with changes in the liability which is linked to changes in the discount rate assumption for re-measurement. We evaluated the effect of this change in accounting method and deemed it immaterial to the historical and current financial statements and therefore did not account for the change retrospectively. Accordingly, the Company calculated the cumulative difference using a calculated value versus fair value to determine market-related value for liability-hedging assets of the portfolio. The cumulative effect of this change, as of January 1, 2020, resulted in a decrease to prior service costs, as recorded in Other income (expense), net, of $0.6 million, an increase in Income tax expense of $0.2 million and an increase to Net income of $0.4 million within the accompanying Condensed Consolidated Statements of Income for the six months ended June 30, 2020. Funding Status of Employee Benefit Plans Based on the fair value of assets and estimated discount rate used to value benefit obligations as of June 30, 2020, we estimate the unfunded status of our employee benefit plans to be approximately $50 million compared to $51 million at December 31, 2019. In 2012, we froze our pension plan and closed it to new participants. Since then, we have implemented various de-risking strategies including lump sum buyouts, the purchase of annuities and the reduction of return-seeking assets over time to a more liability-hedged portfolio. As a result, recent capital markets volatility driven by the COVID-19 pandemic has not materially affected our unfunded status and does not require interim re-measurement of our pension plan assets or defined benefit obligations. 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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Service cost $ 1,353 $ 1,345 $ 2,706 $ 2,691 Interest cost 3,356 4,344 6,713 8,687 Expected return on plan assets (5,648) (6,100) (11,296) (12,200) Prior service cost — 7 — 13 Net loss (gain) 2,093 940 4,186 1,881 Net periodic benefit cost $ 1,154 $ 536 $ 2,309 $ 1,072 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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Service cost $ 514 $ 454 $ 1,028 $ 908 Interest cost 413 563 825 1,123 Expected return on plan assets (46) (58) (91) (115) Prior service (benefit) (137) (100) (274) (199) Net loss (gain) 5 — 10 — Net periodic benefit cost $ 749 $ 859 $ 1,498 $ 1,717 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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Service cost $ 1,817 $ 692 $ 447 $ 1,977 Interest cost 275 324 550 648 Prior service cost — 1 — 1 Net loss (gain) 426 134 852 268 Net periodic benefit cost $ 2,518 $ 1,151 $ 1,849 $ 2,894 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 six months of 2020 and anticipated contributions for 2020 and 2021 are as follows (in thousands): Contributions Made Additional Contributions Contributions Six Months Ended June 30, 2020 Anticipated for 2020 Anticipated for 2021 Defined Benefit Pension Plan $ 12,700 $ — $ 12,700 Non-pension Defined Benefit Postretirement Healthcare Plans $ 2,670 $ 2,671 $ 5,364 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans $ 710 $ 710 $ 1,614

Commitments and Contingencies_

Commitments and Contingencies:	6 Months Ended
	Jun. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies There have been no significant changes to commitments and contingencies from those previously disclosed in Note 19 of our Notes to the Consolidated Financial Statements in our 2019 Annual Report on Form 10-K except for those described below and in Note 5 . Power Sales Agreement - Colorado Electric On July 1, 2020, Colorado Electric entered into a PSA with the City of Colorado Springs to sell up to 60 MW of wind energy purchased from PRPA under a separate PPA. This agreement expires June 30, 2025.

Income Taxes_

Income Taxes:	6 Months Ended
	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes CARES Act On March 27, 2020, the President signed the Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”), which contained, in part, an allowance for deferral of the employer portion of Social Security employment tax liabilities until 2021 and 2022, as well as a COVID-19 employee retention tax credit of up to $5,000 per eligible employee. Eligible employers are taxpayers experiencing either: (1) a full or partial suspension of business operations stemming from a government COVID-19-related order or (2) a more than 50% drop in gross receipts compared to the corresponding calendar quarter in 2019. This 50% employee retention tax credit applies up to $10,000 in qualified wages paid between March 13, 2020 through December 31, 2020, and is refundable to the extent it exceeds the employer portion of payroll tax liability. Eligible wages or employer-paid health benefits must be paid for the period of time during which an employee did not provide services. However, employees do not need to stop providing all services to the employer for the credit to potentially apply. Additionally, the CARES Act accelerates the amount of alternative minimum tax (“AMT”) credits that can be refunded for the 2018 and 2019 annual tax returns. During the second quarter 2020, we utilized the payroll tax deferral provision which allowed us to defer payment of approximately $2.9 million of Social Security employment tax liabilities. We are currently reviewing the potential future benefits of the CARES Act related to employee retention tax credits to assess the impact on our financial position, results of operations and cash flows. Income tax (expense) for the Three Months Ended June 30, 2020 Compared to the Three Months Ended June 30, 2019. Income tax (expense) for the three months ended June 30, 2020 was $(4.8) million compared to $(2.3) million reported for the same period in 2019. For the three months ended June 30, 2020, the effective tax rate was 16.4% compared to 11.5% for the same period in 2019. The higher effective tax rate is primarily due to a prior year discrete tax benefit related to repairs and certain indirect costs. Income tax (expense) for the Six Months Ended June 30, 2020 Compared to the Six Months Ended June 30, 2019. Income tax (expense) for the six months ended June 30, 2020 was $(21) million compared to $(20) million reported for the same period in 2019. For the six months ended June 30, 2020, the effective tax rate was 14.6% compared to 13.5% for the same period in 2019. The higher effective tax rate is primarily due to a prior year discrete tax benefit related to repairs and certain indirect costs and a current year discrete tax adjustment related to the impairment of our investment in equity securities of a privately held oil and gas company partially offset by increased tax benefits from forecasted federal production tax credits associated with new wind assets.

Investments_

Investments:	6 Months Ended
	Jun. 30, 2020
Investments, All Other Investments [Abstract]
Investments	Investments In February 2018, we contributed $28 million of assets in exchange for equity securities in a privately held oil and gas company as we divested our Oil and Gas segment. The carrying value of our investment in the equity securities was recorded at cost. We review this investment on a periodic basis to determine whether a significant event or change in circumstances has occurred that may have an adverse effect on the value of the investment. During the third quarter of 2019, we assessed our investment for impairment as a result of a deterioration in earnings performance of the privately held oil and gas company and an adverse change in future natural gas prices. We engaged a third-party valuation consultant to estimate the fair value of our investment. The valuation was primarily based on an income approach but also considered a market valuation approach. The significant inputs used to estimate the fair value were the oil and gas reserve quantities and values utilizing forward market price curves, industry standard reserve adjustment factors and a discount rate of 10%. Based on the results of the valuation, we concluded that the carrying value of the investment exceeded fair value. As a result, we recorded a pre-tax impairment loss of $20 million for the three months ended September 30, 2019, which was the difference between the carrying value and the fair value of the investment at that time. During the first quarter of 2020, we assessed our investment for impairment as a result of continued adverse changes in future natural gas prices and liquidity concerns at the privately held oil and gas company. We performed an internal analysis to compute the fair value of our investment, utilizing a consistent methodology as applied during the third quarter of 2019. Based on the results of the valuation, we concluded that the carrying value of the investment exceeded fair value. As a result, we recorded a pre-tax impairment loss of $6.9 million for the three months ended March 31, 2020, which was the difference between the carrying value and the fair value of the investment at that time. The following table presents the carrying value of our investments (in thousands) as of: June 30, 2020 December 31, 2019 Investment in privately held oil and gas company $ 1,500 $ 8,359 Cash surrender value of life insurance contracts 13,423 13,056 Other investments 515 514 Total investments $ 15,438 $ 21,929

Subsequent Events_

Subsequent Events:	6 Months Ended
	Jun. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events We evaluated all subsequent event activity and concluded that no subsequent events have occurred that would require recognition in the condensed consolidated financial statements or disclosures, with the exception of those items disclosed in Notes 8 and 13

Management's Statement (Policie

Management's Statement (Policies)	6 Months Ended
	Jun. 30, 2020
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 June 30, 2020, December 31, 2019 and June 30, 2019 financial information. Certain industries in which we operate are highly seasonal and revenue from, and certain expenses for, such operations may fluctuate significantly among quarterly periods. Demand for electricity and natural gas is sensitive to seasonal cooling, heating and industrial load requirements. In particular, the normal peak usage season for electric utilities is June through August while the normal peak usage season for gas utilities is November through March. Significant earnings variances can be expected between the Gas Utilities segment’s peak and off-peak seasons. Due to this seasonal nature, our results of operations for the three and six months ended June 30, 2020 and June 30, 2019, and our financial condition as of June 30, 2020 and December 31, 2019 are not necessarily indicative of the results of operations and financial condition to be expected for any other period. All earnings per share amounts discussed refer to diluted earnings per share unless otherwise noted.
Reclassification	Reclassification We changed certain classifications of operating expenses on the Condensed Consolidated Statements of Income for the three and six months ended June 30, 2019 to conform with current year presentation. The prior year reclassifications, which are shown in the table below, did not impact previously reported operating income or net income. Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 (in millions) Fuel, purchased power and cost of natural gas sold $ 0.4 $ 1.3 Operations and maintenance — (0.3) Taxes - property and production — (0.2) Other operating expenses (0.4) (0.8) $ — $ —
Change in Accounting Principle - Pension Accounting Asset Method	Change in Accounting Principle - Pension Accounting Asset Method Effective January 1, 2020, we changed our method of accounting for net periodic benefit cost. Prior to the change, the Company used a calculated value for determining market-related value of plan assets which amortized the effects of gains and losses over a five-year period. Effective with the accounting change, the Company will use a calculated value for the return-seeking assets (equities) in the portfolio and change to fair value for the liability-hedging assets (fixed income). See Note 12 for additional information.
Recently Issued and Adopted Accounting Standards	Recently Issued 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. The new guidance is effective for interim and annual periods beginning after December 15, 2020 with early adoption permitted. We are currently reviewing this standard to assess the impact on our financial position, results of operations and cash flows. Recently Adopted Accounting Standards Financial Instruments -- Credit Losses: Measurement of Credit Losses on Financial Instruments, ASU 2016-13 In June 2016, the FASB issued ASU 2016-13, Financial Instruments -- Credit Losses: Measurement of Credit Losses on Financial Instruments, which was subsequently amended by ASUs 2018-19, 2019-04, 2019-05, 2019-10, and 2019-11. The standard introduces new accounting guidance for credit losses on financial instruments within its scope, including trade receivables. This new guidance adds an impairment model that is based on expected losses rather than incurred losses. We adopted this standard on January 1, 2020 with prior year comparative financial information remaining as previously reported when transitioning to the new standard. On January 1, 2020, we recorded an increase to our allowance for credit losses, primarily associated with the inclusion of expected losses on unbilled revenue. The cumulative effect of the adoption, net of tax impact, was $0.2 million, which was recorded as an adjustment to retained earnings. Simplifying the Test for Goodwill Impairment, ASU 2017-04 In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment, by eliminating step 2 from the goodwill impairment test. Under the new guidance, if the carrying amount of a reporting unit exceeds its fair value, an impairment loss will be recognized in an amount equal to that excess, limited to the amount of goodwill allocated to that reporting unit. We adopted this standard prospectively on January 1, 2020. Adoption of this guidance, in conjunction with the annual goodwill impairment test as of October 1, 2020, is not expected to have an impact on our financial position, results of operations or cash flows. Internal-Use Software: Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, ASU 2018-15 In August 2018, the FASB issued ASU 2018-15, Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract , which aligns the requirements for recording implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. As a result, certain categories of implementation costs that previously would have been charged to expense as incurred are now capitalized as prepayments and amortized over the term of the arrangement. We adopted this standard prospectively on January 1, 2020. Adoption of this guidance did not have a material 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 4 .

Organization, Consolidation and

Organization, Consolidation and Presentation of Financial Statements (Tables)	6 Months Ended
	Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Reclassification	The prior year reclassifications, which are shown in the table below, did not impact previously reported operating income or net income. Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 (in millions) Fuel, purchased power and cost of natural gas sold $ 0.4 $ 1.3 Operations and maintenance — (0.3) Taxes - property and production — (0.2) Other operating expenses (0.4) (0.8) $ — $ —

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 30, 2020
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 reporting segments for the three and six months ended June 30, 2020 and 2019. Sales tax and other similar taxes are excluded from revenues. Three Months Ended June 30, 2020 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 141,804 $ 120,594 $ — $ 14,846 $ (7,916) $ 269,328 Transportation — 30,792 — — (138) 30,654 Wholesale 3,470 — 25,718 — (24,476) 4,712 Market - off-system sales 3,538 23 — — (1,580) 1,981 Transmission/Other 12,761 9,189 — — (4,432) 17,518 Revenue from contracts with customers $ 161,573 $ 160,598 $ 25,718 $ 14,846 $ (38,542) $ 324,193 Other revenues 1,627 512 404 570 (392) 2,721 Total revenues $ 163,200 $ 161,110 $ 26,122 $ 15,416 $ (38,934) $ 326,914 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 14,846 $ (7,916) $ 6,930 Services transferred over time 161,573 160,598 25,718 — (30,626) 317,263 Revenue from contracts with customers $ 161,573 $ 160,598 $ 25,718 $ 14,846 $ (38,542) $ 324,193 Three Months Ended June 30, 2019 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer Types: Retail $ 139,732 $ 123,630 $ — $ 12,428 $ (7,041) $ 268,749 Transportation — 28,623 — — (276) 28,347 Wholesale 6,781 — 15,062 — (13,296) 8,547 Market - off-system sales 3,448 161 — — (1,335) 2,274 Transmission/Other 14,416 11,612 — — (4,199) 21,829 Revenue from contracts with customers $ 164,377 $ 164,026 $ 15,062 $ 12,428 $ (26,147) $ 329,746 Other revenues 1,977 1,443 9,646 617 (9,541) 4,142 Total Revenues $ 166,354 $ 165,469 $ 24,708 $ 13,045 $ (35,688) $ 333,888 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 12,428 $ (7,041) $ 5,387 Services transferred over time 164,377 164,026 15,062 — (19,106) 324,359 Revenue from contracts with customers $ 164,377 $ 164,026 $ 15,062 $ 12,428 $ (26,147) $ 329,746 Six Months Ended June 30, 2020 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 290,444 $ 418,841 $ — $ 29,249 $ (15,755) $ 722,779 Transportation — 74,900 — — (277) 74,623 Wholesale 9,022 — 51,185 — (48,088) 12,119 Market - off-system sales 8,405 161 — — (4,219) 4,347 Transmission/Other 27,618 21,761 — — (8,845) 40,534 Revenue from contracts with customers $ 335,489 $ 515,663 $ 51,185 $ 29,249 $ (77,184) $ 854,402 Other revenues 1,850 6,220 903 1,372 (783) 9,562 Total revenues $ 337,339 $ 521,883 $ 52,088 $ 30,621 $ (77,967) $ 863,964 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 29,249 $ (15,755) $ 13,494 Services transferred over time 335,489 515,663 51,185 — (61,429) 840,908 Revenue from contracts with customers $ 335,489 $ 515,663 $ 51,185 $ 29,249 $ (77,184) $ 854,402 Six Months Ended June 30, 2019 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer Types: Retail $ 293,195 $ 477,905 $ — $ 28,257 $ (15,169) $ 784,188 Transportation — 73,140 — — (708) 72,432 Wholesale 15,124 — 30,531 — (26,509) 19,146 Market - off-system sales 10,140 378 — — (3,559) 6,959 Transmission/Other 28,591 24,802 — — (8,402) 44,991 Revenue from contracts with customers $ 347,050 $ 576,225 $ 30,531 $ 28,257 $ (54,347) $ 927,716 Other revenues 2,231 324 19,422 1,217 (19,212) 3,982 Total Revenues $ 349,281 $ 576,549 $ 49,953 $ 29,474 $ (73,559) $ 931,698 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 28,257 $ (15,169) $ 13,088 Services transferred over time 347,050 576,225 30,531 — (39,178) 914,628 Revenue from contracts with customers $ 347,050 $ 576,225 $ 30,531 $ 28,257 $ (54,347) $ 927,716

Business Segment Information (T

Business Segment Information (Tables)	6 Months Ended
	Jun. 30, 2020
Segment Reporting Information, Additional Information [Abstract]
Segment Reporting	Segment and Corporate and Other information is as follows (in thousands): Three Months Ended June 30, 2020 External Operating Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 156,197 $ 1,627 $ 5,376 $ — $ 163,200 Gas Utilities 159,824 512 774 — 161,110 Power Generation 1,242 349 24,476 55 26,122 Mining 6,930 233 7,916 337 15,416 Inter-company eliminations — — (38,542) (392) (38,934) Total $ 324,193 $ 2,721 $ — $ — $ 326,914 Three Months Ended June 30, 2019 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 159,140 $ 1,977 $ 5,237 $ — $ 166,354 Gas Utilities 163,303 1,443 723 — 165,469 Power Generation 1,765 434 13,297 9,212 24,708 Mining 5,538 288 6,890 329 13,045 Inter-company eliminations — — (26,147) (9,541) (35,688) Total $ 329,746 $ 4,142 $ — $ — $ 333,888 Six Months Ended June 30, 2020 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 323,700 $ 1,850 $ 11,789 $ — $ 337,339 Gas Utilities 514,111 6,220 1,552 — 521,883 Power Generation 3,097 792 48,088 111 52,088 Mining 13,494 700 15,755 672 30,621 Inter-company eliminations — — (77,184) (783) (77,967) Total $ 854,402 $ 9,562 $ — $ — $ 863,964 Six Months Ended June 30, 2019 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 335,803 $ 2,231 $ 11,247 $ — $ 349,281 Gas Utilities 574,803 324 1,422 — 576,549 Power Generation 4,022 870 26,509 18,552 49,953 Mining 13,088 557 15,169 660 29,474 Inter-company eliminations — — (54,347) (19,212) (73,559) Total $ 927,716 $ 3,982 $ — $ — $ 931,698 Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Adjusted operating income (a) : Electric Utilities $ 33,993 $ 33,546 $ 69,643 $ 74,566 Gas Utilities 18,209 8,557 121,106 111,871 Power Generation 11,402 10,156 22,751 22,123 Mining 3,358 1,640 6,487 5,977 Corporate and Other (29) 102 131 (405) Operating income 66,933 54,001 220,118 214,132 Interest expense, net (35,545) (34,264) (70,998) (68,981) Impairment of investment — — (6,859) — Other income (expense), net (1,863) 263 490 (526) Income tax (expense) (4,831) (2,307) (20,833) (19,570) Net income 24,694 17,693 121,918 125,055 Net income attributable to noncontrolling interest (3,728) (3,110) (7,778) (6,664) Net income available for common stock $ 20,966 $ 14,583 $ 114,140 $ 118,391 __________ (a) Adjusted operating income recognizes intersegment revenues and costs for Colorado Electric’s PPA with Black Hills Colorado IPP on an accrual basis rather than as a finance lease. This presentation of segment information does not impact consolidated financial results.
Reconciliation of Assets from Segment to Consolidated	Segment and Corporate and Other balances included in the accompanying Condensed Consolidated Balance Sheets were as follows (in thousands): Total assets (net of inter-company eliminations) as of: June 30, 2020 December 31, 2019 Segment: Electric Utilities $ 2,982,841 $ 2,900,983 Gas Utilities 4,052,860 4,032,339 Power Generation 407,107 417,715 Mining 79,774 77,175 Corporate and Other 167,350 130,245 Total assets $ 7,689,932 $ 7,558,457

Selected Balance Sheet Inform_2

Selected Balance Sheet Information (Tables)	6 Months Ended
	Jun. 30, 2020
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: June 30, 2020 December 31, 2019 Accounts receivable, trade $ 122,650 $ 144,747 Unbilled revenue 55,915 113,502 Less: Allowance for credit losses (7,585) (2,444) Accounts receivable, net $ 170,980 $ 255,805
Financing Receivable, Current, Allowance for Credit Loss	Changes to allowance for credit losses for the six months ended June 30, 2020 and 2019, 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 June 30, 2020 $ 2,444 $ 6,715 $ 2,203 $ (3,777) $ 7,585 2019 $ 3,209 $ 4,913 $ 1,870 $ (4,906) $ 5,086
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: June 30, 2020 December 31, 2019 Materials and supplies $ 92,284 $ 82,809 Fuel - Electric Utilities 3,574 2,425 Natural gas in storage 10,129 31,938 Total materials, supplies and fuel $ 105,987 $ 117,172
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: June 30, 2020 December 31, 2019 Accrued employee compensation, benefits and withholdings $ 59,701 $ 62,837 Accrued property taxes 36,832 44,547 Customer deposits and prepayments 45,143 54,728 Accrued interest 31,757 31,868 Other (none of which is individually significant) 28,234 32,787 Total accrued liabilities $ 201,667 $ 226,767

Regulatory Matters (Tables)

Regulatory Matters (Tables)	6 Months Ended
	Jun. 30, 2020
Regulatory Assets and Liabilities Disclosure [Abstract]
Schedule of Regulatory Assets and Liabilities	We had the following regulatory assets and liabilities (in thousands) as of: June 30, 2020 December 31, 2019 Regulatory assets Deferred energy and fuel cost adjustments (a) $ 36,900 $ 34,088 Deferred gas cost adjustments (a) 226 1,540 Gas price derivatives (a) 662 3,328 Deferred taxes on AFUDC (b) 7,715 7,790 Employee benefit plans (c) 115,416 115,900 Environmental (a) 1,426 1,454 Loss on reacquired debt (a) 23,820 24,777 Renewable energy standard adjustment (a) 1 1,622 Deferred taxes on flow through accounting (c) 44,940 41,220 Decommissioning costs (b) 9,854 10,670 Gas supply contract termination (a) 5,521 8,485 Other regulatory assets (a) 25,831 20,470 Total regulatory assets 272,312 271,344 Less current regulatory assets (51,745) (43,282) Regulatory assets, non-current $ 220,567 $ 228,062 Regulatory liabilities Deferred energy and gas costs (a) $ 28,279 $ 17,278 Employee benefit plan costs and related deferred taxes (c) 41,025 43,349 Cost of removal (a) 168,137 166,727 Excess deferred income taxes (c) 288,796 285,438 TCJA revenue reserve 3,027 3,418 Other regulatory liabilities (c) 36,557 20,442 Total regulatory liabilities 565,821 536,652 Less current regulatory liabilities (59,428) (33,507) Regulatory liabilities, non-current $ 506,393 $ 503,145 __________ (a) Recovery of costs, but we are not allowed a rate of return. (b) In addition to recovery of costs, we are allowed a rate of return. (c) 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.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 2020
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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Net income available for common stock $ 20,966 $ 14,583 $ 114,140 $ 118,391 Weighted average shares - basic 62,573 60,467 62,175 60,195 Dilutive effect of: Equity compensation 44 139 55 138 Weighted average shares - diluted 62,617 60,606 62,230 60,333 Earnings per share of common stock: Earnings per share, Basic $ 0.34 $ 0.24 $ 1.84 $ 1.97 Earnings per share, Diluted $ 0.33 $ 0.24 $ 1.83 $ 1.96
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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Equity compensation 29 — 26 — Restricted stock 76 — 36 — Anti-dilutive shares 105 — 62 —

Notes Payable, Current Maturi_2

Notes Payable, Current Maturities and Debt (Tables)	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Schedule of Short-term Debt	We had the following short-term debt outstanding in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: June 30, 2020 December 31, 2019 Balance Outstanding Letters of Credit (a) Balance Outstanding Letters of Credit (a) Revolving Credit Facility $ — $ 11,999 $ — $ 30,274 CP Program — — 349,500 — Total $ — $ 11,999 $ 349,500 $ 30,274 _______________ (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 June 30, 2020: As of June 30, 2020 Covenant Requirement Consolidated Indebtedness to Capitalization Ratio 58.7% Less than 65%

Risk Management and Derivativ_2

Risk Management and Derivatives (Tables)	6 Months Ended
	Jun. 30, 2020
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: June 30, 2020 December 31, 2019 Units Notional Maximum Term (months) (a) Notional Maximum Term (months) (a) Natural gas futures purchased MMBtus 660,000 9 1,450,000 12 Natural gas options purchased, net MMBtus 950,000 9 3,240,000 3 Natural gas basis swaps purchased MMBtus 520,000 6 1,290,000 12 Natural gas over-the-counter swaps, net (b) MMBtus 6,480,000 23 4,600,000 24 Natural gas physical contracts, net (c) MMBtus 8,085,376 9 13,548,235 12 Electric wholesale contracts (c) MWh 141,225 6 — 0 __________ (a) Term reflects the maximum forward period hedged. (b) As of June 30, 2020, 1,776,900 MMBtus of natural gas over-the-counter swaps purchases were designated as cash flow hedges.
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 June 30, 2020 December 31, 2019 Derivatives designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 66 $ 1 Noncurrent commodity derivatives Other assets, non-current 83 3 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current (324) (490) Noncurrent commodity derivatives Other deferred credits and other liabilities — (29) Total derivatives designated as hedges $ (175) $ (515) Derivatives not designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets, current $ 1,515 $ 341 Noncurrent commodity derivatives Other assets, non-current 191 2 Liability derivative instruments: Current commodity derivatives Derivative liabilities, current (297) (1,764) Noncurrent commodity derivatives Other deferred credits and other liabilities (15) (63) Total derivatives not designated as hedges $ 1,394 $ (1,484)
Derivative Instruments, Gain (Loss)	The impacts of cash flow hedges on our Condensed Consolidated Statements of Comprehensive Income and Condensed Consolidated Statements of Income are presented below for the three and six months ended June 30, 2020 and 2019. 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 June 30, Three Months Ended June 30, 2020 2019 2020 2019 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 11 (601) Fuel, purchased power and cost of natural gas sold (70) 83 Total $ 724 $ 112 $ (783) $ (630) Six Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 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 $ 1,426 $ 1,426 Interest expense $ (1,426) $ (1,426) Commodity derivatives 268 (921) Fuel, purchased power and cost of natural gas sold (556) 637 Total $ 1,694 $ 505 $ (1,982) $ (789) Based on June 30, 2020 prices, a $0.2 million gain would be realized, reported in pre-tax earnings and reclassified from AOCI during the next 12 months. As market prices fluctuate, estimated and actual realized gains or losses will change during future periods. Derivatives Not Designated as Hedges The following table summarizes the impacts of derivative instruments not designated as hedge instruments on our Condensed Consolidated Statements of Income for the three and six months ended June 30, 2020 and 2019. 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 June 30, 2020 2019 Derivatives Not Designated as Hedging Instruments Income Statement Location Amount of Gain/(Loss) on Derivatives Recognized in Income Commodity derivatives - Electric Fuel, purchased power and cost of natural gas sold $ (204) $ — Commodity derivatives - Natural Gas Fuel, purchased power and cost of natural gas sold 449 (1,185) $ 245 $ (1,185) Six Months Ended June 30, 2020 2019 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 $ 1,158 $ — Commodity derivatives - Natural Gas Fuel, purchased power and cost of natural gas sold 1,215 (1,160) $ 2,373 $ (1,160)

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2020
Fair Value Disclosures [Abstract]
Schedule of Fair Value Hierarchy, Measured on Recurring Basis	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 to the Consolidated Financial Statements included in our 2019 Annual Report on Form 10-K filed with the SEC. As of June 30, 2020 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Total (in thousands) Assets: Commodity derivatives — Gas Utilities $ — $ 1,114 $ — $ (417) $ 697 Commodity derivatives — Electric Utilities — 1,158 — — 1,158 Total $ — $ 2,272 $ — $ (417) $ 1,855 Liabilities: Commodity derivatives — Gas Utilities $ — $ 1,553 $ — $ (917) $ 636 Total $ — $ 1,553 $ — $ (917) $ 636 As of December 31, 2019 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Total (in thousands) Assets: Commodity derivatives — Gas Utilities $ — $ 1,433 $ — $ (1,085) $ 348 Total $ — $ 1,433 $ — $ (1,085) $ 348 Liabilities: Commodity derivatives — Gas Utilities $ — $ 5,254 $ — $ (2,909) $ 2,345 Total $ — $ 5,254 $ — $ (2,909) $ 2,345
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: June 30, 2020 December 31, 2019 Carrying Fair Value Carrying Fair Value Long-term debt, including current maturities (a) $ 3,537,194 $ 4,051,912 $ 3,145,839 $ 3,479,367 __________ (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 (L_2

Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Jun. 30, 2020
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 Six Months Ended June 30, 2020 2019 2020 2019 Gains and (losses) on cash flow hedges: Interest rate swaps Interest expense $ (713) $ (713) $ (1,426) $ (1,426) Commodity contracts Fuel, purchased power and cost of natural gas sold (70) 83 (556) 637 (783) (630) (1,982) (789) Income tax Income tax benefit (expense) 186 153 471 188 Total reclassification adjustments related to cash flow hedges, net of tax $ (597) $ (477) $ (1,511) $ (601) Amortization of components of defined benefit plans: Prior service cost Operations and maintenance $ 25 $ 20 $ 55 $ 39 Actuarial gain (loss) Operations and maintenance (597) (221) (1,194) (441) (572) (201) (1,139) (402) Income tax Income tax benefit (expense) 176 47 264 95 Total reclassification adjustments related to defined benefit plans, net of tax $ (396) $ (154) $ (875) $ (307) Total reclassifications $ (993) $ (631) $ (2,386) $ (908)
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): 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 — (220) 55 (165) Amounts reclassified from AOCI 1,087 424 875 2,386 As of June 30, 2020 $ (14,035) $ (252) $ (14,147) $ (28,434) Interest Rate Swaps Commodity Derivatives Employee Benefit Plans Total As of December 31, 2018 $ (17,307) $ 328 $ (9,937) $ (26,916) Other comprehensive income (loss) before reclassifications — (219) — (219) Amounts reclassified from AOCI 1,091 (490) 307 908 As of June 30, 2019 $ (16,216) $ (381) $ (9,630) $ (26,227)

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 2020
Defined Benefit Plan [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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Service cost $ 1,353 $ 1,345 $ 2,706 $ 2,691 Interest cost 3,356 4,344 6,713 8,687 Expected return on plan assets (5,648) (6,100) (11,296) (12,200) Prior service cost — 7 — 13 Net loss (gain) 2,093 940 4,186 1,881 Net periodic benefit cost $ 1,154 $ 536 $ 2,309 $ 1,072 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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Service cost $ 514 $ 454 $ 1,028 $ 908 Interest cost 413 563 825 1,123 Expected return on plan assets (46) (58) (91) (115) Prior service (benefit) (137) (100) (274) (199) Net loss (gain) 5 — 10 — Net periodic benefit cost $ 749 $ 859 $ 1,498 $ 1,717 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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Service cost $ 1,817 $ 692 $ 447 $ 1,977 Interest cost 275 324 550 648 Prior service cost — 1 — 1 Net loss (gain) 426 134 852 268 Net periodic benefit cost $ 2,518 $ 1,151 $ 1,849 $ 2,894
Schedule of Defined Benefit Plans Contributions	Contributions made in the first six months of 2020 and anticipated contributions for 2020 and 2021 are as follows (in thousands): Contributions Made Additional Contributions Contributions Six Months Ended June 30, 2020 Anticipated for 2020 Anticipated for 2021 Defined Benefit Pension Plan $ 12,700 $ — $ 12,700 Non-pension Defined Benefit Postretirement Healthcare Plans $ 2,670 $ 2,671 $ 5,364 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans $ 710 $ 710 $ 1,614

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2020
Investments, All Other Investments [Abstract]
Investments	The following table presents the carrying value of our investments (in thousands) as of: June 30, 2020 December 31, 2019 Investment in privately held oil and gas company $ 1,500 $ 8,359 Cash surrender value of life insurance contracts 13,423 13,056 Other investments 515 514 Total investments $ 15,438 $ 21,929

Management's Statement_ Reclass

Management's Statement: Reclassification (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fuel, purchased power and cost of natural gas sold	$ 71,629	$ 90,200	$ 259,508	$ 339,942
Operations and maintenance	117,308	124,950	242,774	248,534
Taxes - property and production	14,381	13,142	28,499	26,467
Operating Expenses	$ 259,981	279,887	$ 643,846	717,566
Scenario, Adjustment
Fuel, purchased power and cost of natural gas sold		400		1,300
Operations and maintenance		0		(300)
Taxes - property and production		0		(200)
Other operating expenses		(400)		(800)
Operating Expenses		$ 0		$ 0

Management's Statement_ Managem

Management's Statement: Management Statement (Details) - USD ($)	Jun. 30, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 2,614,496,000	$ 2,624,423,000		$ 2,464,069,000	$ 2,419,998,000	$ 2,383,702,000	$ 2,287,423,000
Cumulative Effect, Period of Adoption Adjustment
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ (207,000)	$ (200,000)		$ (3,000)	$ 3,390,000

Disaggregation of Revenue (Deta

Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 324,193	$ 329,746	$ 854,402	$ 927,716
Total revenues	(326,914)	(333,888)	(863,964)	(931,698)
Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,930	5,387	13,494	13,088
Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	317,263	324,359	840,908	914,628
Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(2,721)	(4,142)	(9,562)	(3,982)
Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	269,328	268,749	722,779	784,188
Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	30,654	28,347	74,623	72,432
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4,712	8,547	12,119	19,146
Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,981	2,274	4,347	6,959
Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	17,518	21,829	40,534	44,991
Inter-company Revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(38,542)	(26,147)	(77,184)	(54,347)
Total revenues	38,934	35,688	77,967	73,559
Inter-company Revenues | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(7,916)	(7,041)	(15,755)	(15,169)
Inter-company Revenues | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(30,626)	(19,106)	(61,429)	(39,178)
Inter-company Revenues | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	392	9,541	783	19,212
Inter-company Revenues | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(7,916)	(7,041)	(15,755)	(15,169)
Inter-company Revenues | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(138)	(276)	(277)	(708)
Inter-company Revenues | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(24,476)	(13,296)	(48,088)	(26,509)
Inter-company Revenues | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1,580)	(1,335)	(4,219)	(3,559)
Inter-company Revenues | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(4,432)	(4,199)	(8,845)	(8,402)
Electric Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	161,573	164,377	335,489	347,050
Total revenues	(163,200)	(166,354)	(337,339)	(349,281)
Electric Utilities | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Electric Utilities | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	161,573	164,377	335,489	347,050
Electric Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(1,627)	(1,977)	(1,850)	(2,231)
Electric Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	141,804	139,732	290,444	293,195
Electric Utilities | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Electric Utilities | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,470	6,781	9,022	15,124
Electric Utilities | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,538	3,448	8,405	10,140
Electric Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12,761	14,416	27,618	28,591
Gas Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	160,598	164,026	515,663	576,225
Total revenues	(161,110)	(165,469)	(521,883)	(576,549)
Gas Utilities | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Gas Utilities | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	160,598	164,026	515,663	576,225
Gas Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(512)	(1,443)	(6,220)	(324)
Gas Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	120,594	123,630	418,841	477,905
Gas Utilities | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	30,792	28,623	74,900	73,140
Gas Utilities | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Gas Utilities | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	23	161	161	378
Gas Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9,189	11,612	21,761	24,802
Power Generation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	25,718	15,062	51,185	30,531
Total revenues	(26,122)	(24,708)	(52,088)	(49,953)
Power Generation | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Power Generation | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	25,718	15,062	51,185	30,531
Power Generation | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(404)	(9,646)	(903)	(19,422)
Power Generation | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Power Generation | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Power Generation | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	25,718	15,062	51,185	30,531
Power Generation | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Power Generation | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Mining
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,846	12,428	29,249	28,257
Total revenues	(15,416)	(13,045)	(30,621)	(29,474)
Mining | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,846	12,428	29,249	28,257
Mining | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Mining | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(570)	(617)	(1,372)	(1,217)
Mining | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,846	12,428	29,249	28,257
Mining | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Mining | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Mining | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Mining | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0	$ 0	$ 0

Business Segment Information_ I

Business Segment Information: Information Relating to Segment Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended					6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information
Revenue from contracts with customers	$ 324,193			$ 329,746		$ 854,402	$ 927,716
Revenues	(326,914)			(333,888)		(863,964)	(931,698)
Operating income	66,933			54,001		220,118	214,132
Interest expense, net	(35,545)			(34,264)		(70,998)	(68,981)
Impairment of investment	0	$ (6,900)	$ (20,000)	0		(6,859)	0
Other Nonoperating Income (Expense) Including Allowance For Funds Used During Construction, Equity	(1,863)			263		490	(526)
Income tax (expense)	(4,831)			(2,307)		(20,833)	(19,570)
Net income	24,694	$ 97,224		17,693	$ 107,362	121,918	125,055
Net income attributable to noncontrolling interest	(3,728)			(3,110)		(7,778)	(6,664)
Net income available for common stock	20,966			14,583		114,140	118,391
Inter-company Revenues
Segment Reporting Information
Revenue from contracts with customers	(38,542)			(26,147)		(77,184)	(54,347)
Revenues	38,934			35,688		77,967	73,559
Consolidation, Eliminations
Segment Reporting Information
Revenue from contracts with customers	0			0		0	0
Corporate
Segment Reporting Information
Operating income	(29)			102		131	(405)
Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	161,573			164,377		335,489	347,050
Revenues	(163,200)			(166,354)		(337,339)	(349,281)
Operating income	33,993			33,546		69,643	74,566
Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	160,598			164,026		515,663	576,225
Revenues	(161,110)			(165,469)		(521,883)	(576,549)
Operating income	18,209			8,557		121,106	111,871
Power Generation
Segment Reporting Information
Revenue from contracts with customers	25,718			15,062		51,185	30,531
Revenues	(26,122)			(24,708)		(52,088)	(49,953)
Operating income	11,402			10,156		22,751	22,123
Mining
Segment Reporting Information
Revenue from contracts with customers	14,846			12,428		29,249	28,257
Revenues	(15,416)			(13,045)		(30,621)	(29,474)
Operating income	3,358			1,640		6,487	5,977
Other Revenues
Segment Reporting Information
Revenues	(2,721)			(4,142)		(9,562)	(3,982)
Other Revenues | Inter-company Revenues
Segment Reporting Information
Revenues	392			9,541		783	19,212
Other Revenues | Consolidation, Eliminations
Segment Reporting Information
Revenues	0			0		0	0
Other Revenues | Electric Utilities
Segment Reporting Information
Revenues	(1,627)			(1,977)		(1,850)	(2,231)
Other Revenues | Gas Utilities
Segment Reporting Information
Revenues	(512)			(1,443)		(6,220)	(324)
Other Revenues | Power Generation
Segment Reporting Information
Revenues	(404)			(9,646)		(903)	(19,422)
Other Revenues | Mining
Segment Reporting Information
Revenues	(570)			(617)		(1,372)	(1,217)
External Operating Revenue
Segment Reporting Information
Revenue from contracts with customers	324,193			329,746		854,402	927,716
External Operating Revenue | Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	156,197			159,140		323,700	335,803
External Operating Revenue | Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	159,824			163,303		514,111	574,803
External Operating Revenue | Power Generation
Segment Reporting Information
Revenue from contracts with customers	1,242			1,765		3,097	4,022
External Operating Revenue | Mining
Segment Reporting Information
Revenue from contracts with customers	6,930			5,538		13,494	13,088
External Operating Revenue | Other Revenues
Segment Reporting Information
Revenues	(2,721)			(4,142)		(9,562)	(3,982)
External Operating Revenue | Other Revenues | Electric Utilities
Segment Reporting Information
Revenues	(1,627)			(1,977)		(1,850)	(2,231)
External Operating Revenue | Other Revenues | Gas Utilities
Segment Reporting Information
Revenues	(512)			(1,443)		(6,220)	(324)
External Operating Revenue | Other Revenues | Power Generation
Segment Reporting Information
Revenues	(349)			(434)		(792)	(870)
External Operating Revenue | Other Revenues | Mining
Segment Reporting Information
Revenues	(233)			(288)		(700)	(557)
Inter-company Operating Revenue | Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	5,376			5,237		11,789	11,247
Inter-company Operating Revenue | Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	774			723		1,552	1,422
Inter-company Operating Revenue | Power Generation
Segment Reporting Information
Revenue from contracts with customers	24,476			13,297		48,088	26,509
Inter-company Operating Revenue | Mining
Segment Reporting Information
Revenue from contracts with customers	7,916			6,890		15,755	15,169
Inter-company Operating Revenue | Other Revenues | Electric Utilities
Segment Reporting Information
Revenues	0			0		0	0
Inter-company Operating Revenue | Other Revenues | Gas Utilities
Segment Reporting Information
Revenues	0			0		0	0
Inter-company Operating Revenue | Other Revenues | Power Generation
Segment Reporting Information
Revenues	(55)			(9,212)		(111)	(18,552)
Inter-company Operating Revenue | Other Revenues | Mining
Segment Reporting Information
Revenues	$ (337)			$ (329)		$ (672)	$ (660)

Business Segment Information_ S

Business Segment Information: Segment and Corporate Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 7,689,932	$ 7,558,457
Corporate
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	167,350	130,245
Electric Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,982,841	2,900,983
Gas Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	4,052,860	4,032,339
Power Generation
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	407,107	417,715
Mining
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 79,774	$ 77,175

Selected Balance Sheet Inform_3

Selected Balance Sheet Information: Accounts Receivable (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Selected Balance Sheet Information [Abstract]
Accounts receivable, trade	$ 122,650	$ 144,747
Unbilled revenue	55,915	113,502
Less: Allowance for doubtful accounts	(7,585)	(2,444)	$ (5,086)	$ (3,209)
Accounts receivable, net	$ 170,980	$ 255,805

Selected Balance Sheet Inform_4

Selected Balance Sheet Information: Changes to Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable, Allowance for Credit Loss, Current	$ 7,585	$ 7,585	$ 5,086	$ 2,444	$ 3,209
Accounts Receivable, Credit Loss Expense (Reversal)		6,715	4,913
Accounts Receivable, Allowance for Credit Loss, Recovery		2,203	1,870
Accounts Receivable, Allowance for Credit Loss, Writeoff		(3,777)	$ (4,906)
Adjustment Related to COVID-19
Accounts Receivable, Credit Loss Expense (Reversal)	$ 1,500	$ 2,000

Selected Balance Sheet Inform_5

Selected Balance Sheet Information: Materials and Supplies (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Selected Balance Sheet Information [Abstract]
Materials and supplies	$ 92,284	$ 82,809
Fuel - Electric Utilities	3,574	2,425
Natural gas in storage	10,129	31,938
Total materials, supplies and fuel	$ 105,987	$ 117,172

Selected Balance Sheet Inform_6

Selected Balance Sheet Information: Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Selected Balance Sheet Information [Abstract]
Accrued employee compensation, benefits and withholdings	$ 59,701	$ 62,837
Accrued property taxes	36,832	44,547
Customer deposits and prepayments	45,143	54,728
Accrued interest	31,757	31,868
Other (none of which is individually significant)	28,234	32,787
Total accrued liabilities	$ 201,667	$ 226,767

Regulatory Matters (Details)

Regulatory Matters (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Regulatory assets
Regulatory assets	$ 272,312	$ 271,344
Less current regulatory assets	(51,745)	(43,282)
Regulatory assets, non-current	220,567	228,062
Regulatory liabilities
Regulatory liabilities	565,821	536,652
Less current regulatory liabilities	(59,428)	(33,507)
Regulatory liabilities, non-current	506,393	503,145
Deferred energy and gas costs
Regulatory liabilities
Regulatory liabilities	28,279	17,278
Employee benefit plans
Regulatory liabilities
Regulatory liabilities	41,025	43,349
Cost of removal
Regulatory liabilities
Regulatory liabilities	168,137	166,727
Excess deferred income taxes
Regulatory liabilities
Regulatory liabilities	288,796	285,438
TCJA revenue reduction
Regulatory liabilities
Regulatory liabilities	3,027	3,418
Other regulatory liabilities
Regulatory liabilities
Regulatory liabilities	36,557	20,442
Deferred energy and gas costs
Regulatory assets
Regulatory assets	36,900	34,088
Deferred gas cost adjustments
Regulatory assets
Regulatory assets	226	1,540
Gas price derivatives
Regulatory assets
Regulatory assets	662	3,328
Deferred taxes on AFUDC
Regulatory assets
Regulatory assets	7,715	7,790
Employee benefit plans
Regulatory assets
Regulatory assets	115,416	115,900
Environmental
Regulatory assets
Regulatory assets	1,426	1,454
Loss on reacquired debt
Regulatory assets
Regulatory assets	23,820	24,777
Renewable energy standard adjustment
Regulatory assets
Regulatory assets	1	1,622
Deferred taxes on flow through accounting
Regulatory assets
Regulatory assets	44,940	41,220
Decommissioning costs
Regulatory assets
Regulatory assets	9,854	10,670
Gas supply contract termination
Regulatory assets
Regulatory assets	5,521	8,485
Other regulatory assets
Regulatory assets
Regulatory assets	$ 25,831	$ 20,470

Regulatory Matters_ Rate Review

Regulatory Matters: Rate Review (Details) $ in Thousands	Jun. 01, 2020USD ($)utilityMW	May 19, 2020USD ($)	Feb. 01, 2019USD ($)utility
Federal Energy Regulatory Commission (FERC) | Black Hills Wyoming and Wyoming Electric
Public Utilities, General Disclosures [Line Items]
Pending FERC Approval - Number of Megawatts Capacity to be Purchased and Delivered Through Intercompany Agreement | MW	60
Unrecorded Unconditional Purchase Obligation, Term	11 years
Rate Review Filed with the Regulatory Agency | Nebraska Publc Service Commission (NPSC) | Black Hills Energy, Nebraska Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Number of Gas Distribution Territories Consolidating | utility	2
Public Utilities, Requested Rate Increase (Decrease), Amount	$ (17,000)
Public Utilities, Requested Equity Capital Structure, Percentage	50.00%
Public Utilities, Requested Debt Capital Structure, Percentage	50.00%
Public Utilities, Requested Return on Equity, Percentage	10.00%
Rate Review Filed with the Regulatory Agency | Colorado Public Utilities Commission (CPUC) | Black Hills Energy, Colorado Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Number of Gas Distribution Territories Consolidating | utility			2
Public Utilities, Requested Rate Increase (Decrease), Amount			$ (2,500)
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 600
Public Utilities, Approved Return on Equity, Percentage		9.20%

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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income available for common stock	$ 20,966	$ 14,583	$ 114,140	$ 118,391
Weighted average shares - basic (in shares)	62,573	60,467	62,175	60,195
Dilutive effect of:
Equity compensation (in shares)	44	139	55	138
Weighted average shares - diluted (in shares)	62,617	60,606	62,230	60,333
Earnings (loss) per share, Basic (usd per share)	$ 0.34	$ 0.24	$ 1.84	$ 1.97
Earnings (loss) per share, Diluted (usd per share)	$ 0.33	$ 0.24	$ 1.83	$ 1.96

Earnings Per Share_ Anti-diluti

Earnings Per Share: Anti-dilutive shares (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	105	0	62	0
Equity compensation - (in shares)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	29	0	26	0
Restricted Stock (in shares)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	76	0	36	0

Notes Payable, Current Maturi_3

Notes Payable, Current Maturities and Debt: Schedule of Short-term Debt and Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Short-term Debt [Line Items]
Notes payable	$ 0		$ 349,500
Letters of Credit	11,999		30,274
Net (payments) borrowings of short-term debt	(349,500)	$ (83,120)
Commercial Paper
Short-term Debt [Line Items]
Notes payable	0		349,500
Revolving Credit Facility
Short-term Debt [Line Items]
Notes payable	0		0
Letters of Credit	11,999		$ 30,274
Line of Credit Facility, Current Borrowing Capacity	$ 750,000

Notes Payable, Current Maturi_4

Notes Payable, Current Maturities and Debt: Debt Covenants (Details)	Jun. 30, 2020
Line of Credit Facility [Line Items]
Ratio of Indebtedness to Net Capital	0.587
Maximum
Line of Credit Facility [Line Items]
Consolidated Indebtedness to Capitalization Ratio	0.65

Notes Payable, Current Maturi_5

Notes Payable, Current Maturities and Debt: Debt Offering (Details) - Senior Unsecured Notes Due 2030 $ in Thousands	Jun. 17, 2020USD ($)
Debt Instrument [Line Items]
Proceeds from Issuance of Debt	$ 400,000
Debt Instrument, Interest Rate, Stated Percentage	2.50%
Long-term Debt, Term	10 years

Notes Payable, Current Maturi_6

Notes Payable, Current Maturities and Debt: Long-Term Debt (Details) $ in Millions	Mar. 24, 2020USD ($)
Electric Utilities | South Dakota Electric | Bonds Due 2024
Extinguishment of Debt, Amount	$ 2.9

Equity_ Equity Issuance (Detail

Equity: Equity Issuance (Details) - Private Placement $ / shares in Units, shares in Millions, $ in Millions	Feb. 27, 2020USD ($)$ / sharesshares
Sale of Stock, Number of Shares Issued in Transaction | shares	1.2
Sale of Stock, Price Per Share | $ / shares	$ 81.77
Sale of Stock, Consideration Received on Transaction	$ 99
Payments of Stock Issuance Costs	$ 1

Equity_ At-the-Market Equity Of

Equity: At-the-Market Equity Offering Program (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2019	Aug. 03, 2020
At The Market Equity Offering Program Authorized Aggregate Value	$ 300,000
Issuance costs	$ 79	$ 967	$ 492	$ 289
Subsequent Event
At The Market Equity Offering Program Authorized Aggregate Value						$ 400,000
Common Stock
At The Market Equity Offering Program Shares Issued			700,000		900,000
At The Market Equity Program Proceeds from Sale of Stock			$ 49,000		$ 69,000
Issuance costs			$ 500		$ 700

Risk Management and Derivativ_3

Risk Management and Derivatives: Credit Risk (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019
Accounts Receivable, Credit Loss Expense (Reversal)		$ 6,715	$ 4,913
Adjustment Related to COVID-19
Accounts Receivable, Credit Loss Expense (Reversal)	$ 1,500	$ 2,000

Risk Management and Derivativ_4

Risk Management and Derivatives: Utilities (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020USD ($)MMBTUmW	Dec. 31, 2019MMBTUmW
Derivative [Line Items]
Credit Risk Derivative Liabilities, at Fair Value | $	$ 500
Natural Gas, Distribution | Cash Flow Hedging
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	1,776,900
Natural Gas, Distribution | Natural gas futures purchased
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	660,000	1,450,000
Derivative, Remaining Maturity	9 months	12 months
Natural Gas, Distribution | Natural gas options purchased, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	950,000	3,240,000
Derivative, Remaining Maturity	9 months	3 months
Natural Gas, Distribution | Natural gas basis swaps purchased
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	520,000	1,290,000
Derivative, Remaining Maturity	6 months	12 months
Natural Gas, Distribution | Natural gas over-the-counter swaps, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	6,480,000	4,600,000
Derivative, Remaining Maturity	23 months	24 months
Natural Gas, Distribution | Natural gas physical contracts, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	8,085,376	13,548,235
Derivative, Remaining Maturity	9 months	12 months
Electricity | Electric wholesale contracts
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | mW	141,225	0
Derivative, Remaining Maturity	6 months	0 months

Risk Management and Derivativ_5

Risk Management and Derivatives: Derivatives by Balance Sheet Classification (Details) - Commodity Contract - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair Value Hedges, Net	$ (175)	$ (515)
Designated as Hedging Instrument | Derivative assets — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	66	1
Designated as Hedging Instrument | Other assets, non-current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	83	3
Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	(324)	(490)
Designated as Hedging Instrument | Other deferred credits and other liabilities
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	0	(29)
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair Value Hedges, Net	1,394	(1,484)
Not Designated as Hedging Instrument | Derivative assets — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	1,515	341
Not Designated as Hedging Instrument | Other assets, non-current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Assets	191	2
Not Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	(297)	(1,764)
Not Designated as Hedging Instrument | Other deferred credits and other liabilities
Derivatives, Fair Value [Line Items]
Fair Value Hedge Liabilities	$ (15)	$ (63)

Risk Management and Derivativ_6

Risk Management and Derivatives: Derivatives Designated as Hedges (Details) - Cash Flow Hedging - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (783)	$ (630)	$ (1,982)	$ (789)
Designated as Hedging Instrument
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	724	112	1,694	505
Natural Gas, Distribution
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			200
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	1,426	1,426
Commodity Contract | Designated as Hedging Instrument
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	11	(601)	268	(921)
Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) | Interest rate swaps
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(713)	(713)	(1,426)	(1,426)
Cost of Sales | Commodity Contract
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (70)	$ 83	$ (556)	$ 637

Risk Management and Derivativ_7

Risk Management and Derivatives: Derivatives Not Designated as Hedge Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Derivative [Line Items]
Regulatory assets	$ 272,312		$ 272,312		$ 271,344
Gas price derivatives
Derivative [Line Items]
Regulatory assets	662		662		$ 3,328
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	245	$ (1,185)	2,373	$ (1,160)
Not Designated as Hedging Instrument | Cost of Sales | Electricity
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(204)	0	1,158	0
Not Designated as Hedging Instrument | Cost of Sales | Natural Gas, Distribution
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 449	$ (1,185)	$ 1,215	$ (1,160)

Fair Value Measurements_ Schedu

Fair Value Measurements: Schedule of Fair Values (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
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	$ (417)	$ (1,085)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(917)	(2,909)
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	1,855	348
Derivative Liabilities, Total	636	2,345
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	2,272	1,433
Derivative Liabilities, Total	1,553	5,254
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	(417)	(1,085)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(917)	(2,909)
Gas Utilities | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	697	348
Derivative Liabilities, Fair Value Disclosure	636	2,345
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	1,114	1,433
Derivative Liabilities, Fair Value Disclosure	1,553	5,254
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
Electric Utilities | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	1,158
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
Electric Utilities | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	1,158
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

Fair Value Measurements_ Other

Fair Value Measurements: Other Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 3,537,194	$ 3,145,839
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 4,051,912	$ 3,479,367

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss): Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Condensed Statement of Income Captions [Line Items]
Interest Expense	$ 35,765		$ 34,660		$ 71,546	$ 69,676
Fuel, purchased power and cost of natural gas sold	71,629		90,200		259,508	339,942
Operations and maintenance	117,308		124,950		242,774	248,534
Income before Income Taxes	29,525		20,000		142,751	144,625
Income tax benefit (expense)	(4,831)		(2,307)		(20,833)	(19,570)
Net income (loss)	24,694	$ 97,224	17,693	$ 107,362	121,918	125,055
Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Net income (loss)	(993)		(631)		(2,386)	(908)
Cash Flow Hedging | Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Income before Income Taxes	(783)		(630)		(1,982)	(789)
Income tax benefit (expense)	186		153		471	188
Net income (loss)	(597)		(477)		(1,511)	(601)
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		20		55	39
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	(597)		(221)		(1,194)	(441)
Accumulated Defined Benefit Plans Adjustment | Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Income before Income Taxes	(572)		(201)		(1,139)	(402)
Income tax benefit (expense)	176		47		264	95
Net income (loss)	(396)		(154)		(875)	(307)
Interest rate swaps | Cash Flow Hedging | Reclassification out of Accumulated Other Comprehensive Income
Condensed Statement of Income Captions [Line Items]
Interest Expense	(713)		(713)		(1,426)	(1,426)
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	$ (70)		$ 83		$ (556)	$ 637

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss): Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	$ (30,655)	$ (26,916)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(28,434)	(26,227)
Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	(15,077)	(9,937)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	55	0
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(14,147)	(9,630)
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	875	307
Accumulated Other Comprehensive Income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(165)	(219)
Accumulated Other Comprehensive Income (loss) | Reclassification out of Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	2,386	908
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	(15,122)	(17,307)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(14,035)	(16,216)
Interest Rate Swaps | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent | Reclassification out of Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1,087	1,091
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	(456)	328
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(220)	(219)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(252)	(381)
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	$ 424	$ (490)

Employee Benefit Plans_ Change

Employee Benefit Plans: Change in Accounting Principle (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Other income (expense), net	$ (1,863)	$ 263	$ 490	$ (526)
Income tax (expense)	(4,831)	(2,307)	(20,833)	(19,570)
Net income available for common stock	$ 20,966	$ 14,583	114,140	$ 118,391
Cumulative Effect, Period of Adoption Adjustment
Defined Benefit Plan Disclosure [Line Items]
Other income (expense), net			600
Income tax (expense)			200
Net income available for common stock			$ 400

Employee Benefit Plans_ Funding

Employee Benefit Plans: Funding Status of Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Benefit plan liabilities	$ 142,580		$ 142,580		$ 154,472
Other income (expense), net	(1,863)	$ 263	490	$ (526)
Pension Plan
Benefit plan liabilities	$ 50,000		$ 50,000		$ 51,000

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 1,353	$ 1,345	$ 2,706	$ 2,691
Interest cost	3,356	4,344	6,713	8,687
Expected return on plan assets	(5,648)	(6,100)	(11,296)	(12,200)
Prior service cost (benefit)	0	7	0	13
Net loss (gain)	2,093	940	4,186	1,881
Net periodic benefit cost	1,154	536	2,309	1,072
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer			12,700
Estimated Future Employer Contributions in Current Fiscal Year	0		0
Estimated Future Employer Contributions in Next Fiscal Year	12,700		12,700
Other Postretirement Benefits Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	514	454	1,028	908
Interest cost	413	563	825	1,123
Expected return on plan assets	(46)	(58)	(91)	(115)
Prior service cost (benefit)	(137)	(100)	(274)	(199)
Net loss (gain)	5	0	10	0
Net periodic benefit cost	749	859	1,498	1,717
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer			2,670
Estimated Future Employer Contributions in Current Fiscal Year	2,671		2,671
Estimated Future Employer Contributions in Next Fiscal Year	5,364		5,364
Supplemental Non-qualified Defined Benefit and Defined Contribution Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	1,817	692	447	1,977
Interest cost	275	324	550	648
Prior service cost (benefit)	0	1	0	1
Net loss (gain)	426	134	852	268
Net periodic benefit cost	2,518	$ 1,151	1,849	$ 2,894
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer			710
Estimated Future Employer Contributions in Current Fiscal Year	710		710
Estimated Future Employer Contributions in Next Fiscal Year	$ 1,614		$ 1,614

Commitments and Contingencies_

Commitments and Contingencies: Future Purchase Agreement - Related Party (Details)	Jul. 01, 2020MW
Colorado Electric | City of Colorado Springs | Subsequent Event
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of Megawatts Capacity Purchased	60

Income Taxes_ CARES Act (Detail

Income Taxes: CARES Act (Details) $ in Thousands	Jun. 30, 2020USD ($)
Income Tax Disclosure [Abstract]
Amount of Payroll Tax (Social Security Employment Tax) Deferral Allowed Under the CARES Act	$ 2,900

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Income tax benefit (expense)	$ (4,831)	$ (2,307)	$ (20,833)	$ (19,570)
Effective Tax Rate	16.40%	11.50%	14.60%	13.50%

Investments (Details)

Investments (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Feb. 28, 2018
Assets used to Acquire Other Investments								$ 28,000
Impairment of investment	$ 0	$ 6,900	$ 20,000	$ 0	$ 6,859	$ 0
Investments	15,438				15,438		$ 21,929
Investment in privately held oil and gas company
Investments	1,500				1,500		8,359
Cash surrender value of life insurance contracts
Investments	13,423				13,423		13,056
Other investments
Investments	$ 515				$ 515		$ 514
Valuation, Income Approach
Discount Rate Used in Valuation of Fair Value of Oil and Gas Reserve Quantities			10.00%