Black Hills (BKH) 10-Q 5 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information Document - shares	9 Months Ended
	Sep. 30, 2019	Oct. 31, 2019
Document and Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
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		61,454,071
Entity Central Index Key	0001130464
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenues	$ 325,548	$ 321,979	$ 1,257,246	$ 1,253,072
Operating expenses:
Fuel, purchased power and cost of natural gas sold	73,090	80,244	411,695	432,544
Operations and maintenance	117,037	115,699	366,907	352,092
Depreciation, depletion and amortization	51,884	49,046	154,507	146,345
Taxes - property and production	12,986	11,905	39,454	39,181
Total operating expenses	254,997	256,894	972,563	970,162
Operating income	70,551	65,085	284,683	282,910
Interest charges -
Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts)	(36,200)	(36,380)	(108,232)	(107,183)
Allowance for funds used during construction - borrowed	2,200	701	4,555	1,345
Interest income	513	382	1,208	1,012
Allowance for funds used during construction - equity	311	193	486	503
Impairment of investment	(19,741)	0	(19,741)	0
Other income (expense), net	269	(703)	(431)	(2,426)
Total other income (expense)	(52,648)	(35,807)	(122,155)	(106,749)
Income before income taxes	17,903	29,278	162,528	176,161
Income tax benefit (expense)	(2,508)	(7,477)	(22,078)	11,784
Income from continuing operations	15,395	21,801	140,450	187,945
Net (loss) from discontinued operations	0	(857)	0	(5,627)
Net income	15,395	20,944	140,450	182,318
Net income attributable to noncontrolling interest	(3,655)	(3,994)	(10,319)	(10,447)
Net income available for common stock	11,740	16,950	130,131	171,871
Net income from continuing operations	$ 11,740	$ 17,807	$ 130,131	$ 177,498
Earnings Per Share, Basic [Abstract]
Income from continuing operations, Basic (usd per share)	$ 0.19	$ 0.33	$ 2.15	$ 3.33
(Loss) from discontinued operations, Basic (usd per share)	0	(0.02)	0	(0.10)
Earnings (loss) per share, Basic (usd per share)	0.19	0.32	2.15	3.22
Earnings Per Share, Diluted [Abstract]
Income from continuing operations, Diluted (usd per share)	0.19	0.32	2.15	3.26
(Loss) from discontinued operations, Diluted (usd per share)	0	(0.02)	0	(0.10)
Earnings (loss) per share, Diluted (usd per share)	$ 0.19	$ 0.31	$ 2.15	$ 3.15
Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract]
Basic (in shares)	60,976	53,364	60,458	53,346
Diluted (in shares)	61,104	54,819	60,578	54,508

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net income	$ 15,395	$ 20,944	$ 140,450	$ 182,318
Other comprehensive income (loss), net of tax:
Reclassification adjustments of benefit plan liability - prior service cost (net of tax of $3, $10, $13 and $29, respectively)	(16)	(34)	(45)	(104)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax	(9)	483	327	1,456
Other comprehensive income, net of tax	532	1,060	1,221	3,481
Comprehensive income	15,927	22,004	141,671	185,799
Less: comprehensive income attributable to noncontrolling interest	(3,655)	(3,994)	(10,319)	(10,447)
Comprehensive income available for common stock	12,272	18,010	131,352	175,352
Interest rate swaps
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses	548	560	1,639	1,682
Commodity Contract
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses	124	21	(366)	615
Net unrealized gains (losses) on commodity derivatives (net of tax of $35, $0, $100 and $51, respectively)	$ (115)	$ 30	$ (334)	$ (168)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification adjustment of benefit plan - prior service cost, (tax) benefit	$ 3	$ 10	$ 13	$ 29
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	(92)	(138)	(197)	(409)
Interest rate swaps
Reclassification of net realized gains/losses, (tax) benefit	(165)	(152)	(500)	(456)
Commodity Contract
Net unrealized gains/losses on commodity derivatives, (tax) benefit	35	0	100	51
Reclassification of net realized gains/losses, (tax) benefit	$ (5)	$ 3	$ 142	$ (187)

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 13,087	$ 20,776
Restricted cash	3,688	3,369
Accounts receivable, net	148,989	269,153
Materials, supplies and fuel	123,002	117,299
Derivative assets, current	412	1,500
Income tax receivable, net	12,931	12,978
Regulatory assets, current	46,206	48,776
Other current assets	29,106	29,982
Total current assets	377,421	503,833
Investments	21,583	41,013
Property, plant and equipment	6,567,229	6,000,015
Less: accumulated depreciation and depletion	(1,243,794)	(1,145,136)
Total property, plant and equipment, net	5,323,435	4,854,879
Other assets:
Goodwill	1,299,454	1,299,454
Intangible assets, net	13,566	14,337
Regulatory assets, non-current	214,152	235,459
Other assets, non-current	25,339	14,352
Total other assets, non-current	1,552,511	1,563,602
TOTAL ASSETS	7,274,950	6,963,327
Current liabilities:
Accounts payable	145,085	210,609
Accrued liabilities	217,832	215,501
Derivative liabilities, current	2,396	947
Regulatory liabilities, current	25,168	29,810
Notes payable	294,900	185,620
Current maturities of long-term debt	5,743	5,743
Total current liabilities	691,124	648,230
Long-term debt	3,049,235	2,950,835
Deferred credits and other liabilities:
Deferred income tax liabilities, net	347,952	311,331
Regulatory liabilities, non-current	498,773	510,984
Benefit plan liabilities	134,150	145,147
Other deferred credits and other liabilities	120,820	109,377
Total deferred credits and other liabilities	1,101,695	1,076,839
Commitments and contingencies (See Notes 8, 10, 15, 16)
Equity:
Common stock $1 par value; 100,000,000 shares authorized; issued 61,480,640 and 60,048,567 shares, respectively	61,481	60,049
Additional paid-in capital	1,553,190	1,450,569
Retained earnings	742,138	700,396
Treasury stock, at cost – 26,572 and 44,253 shares, respectively	(1,636)	(2,510)
Accumulated other comprehensive income (loss)	(25,695)	(26,916)
Total stockholders’ equity	2,329,478	2,181,588
Noncontrolling interest	103,418	105,835
Total equity	2,432,896	2,287,423
TOTAL LIABILITIES AND TOTAL EQUITY	$ 7,274,950	$ 6,963,327

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Common Stock, Par Value (usd per share)	$ 1	$ 1
Common Stock, Shares Issued	61,480,640	60,048,567
Treasury Stock, Shares	26,572	44,253
Common Stock, Shares Authorized	100,000,000	100,000,000

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities:
Net income	$ 140,450	$ 182,318
Loss from discontinued operations, net of tax	0	5,627
Income from continuing operations	140,450	187,945
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	154,507	146,345
Deferred financing cost amortization	6,326	5,682
Impairment of investment	19,741	0
Stock compensation	8,332	7,544
Deferred income taxes	24,381	(14,396)
Employee benefit plans	7,965	10,641
Other adjustments, net	9,192	7,668
Changes in certain operating assets and liabilities:
Materials, supplies and fuel	(4,126)	(8,380)
Accounts receivable, unbilled revenues and other operating assets	115,325	72,061
Accounts payable and other operating liabilities	(83,436)	(86,604)
Regulatory assets - current	12,455	41,655
Regulatory liabilities - current	(15,644)	21,416
Contributions to defined benefit pension plans	(12,700)	(12,700)
Other operating activities, net	3,307	2,007
Net cash provided by operating activities of continuing operations	386,075	380,884
Net cash provided by (used in) operating activities of discontinued operations	0	(2,162)
Net cash provided by operating activities	386,075	378,722
Investing activities:
Property, plant and equipment additions	(592,537)	(278,132)
Purchase of investment	0	(24,429)
Other investing activities	(735)	2,766
Net cash provided by (used in) investing activities of continuing operations	(593,272)	(299,795)
Net cash provided by investing activities of discontinued operations	0	18,024
Net cash provided by (used in) investing activities	(593,272)	(281,771)
Financing activities:
Dividends paid on common stock	(91,779)	(76,309)
Common stock issued	101,361	1,079
Net (payments) borrowings of short-term debt	109,280	(99,200)
Long-term debt - repayments	400,000	700,000
Long-term debt - repayments	(304,307)	(603,307)
Distributions to noncontrolling interest	(12,736)	(13,755)
Other financing activities	(1,992)	(10,457)
Net cash provided by (used in) financing activities	199,827	(101,949)
Net change in cash, cash equivalents and restricted cash	(7,370)	(4,998)
Cash, cash equivalents and restricted cash at beginning of period	24,145	18,240
Cash, cash equivalents and restricted cash at end of period	$ 16,775	$ 13,242

Condensed Consolidated Statem_5

Condensed Consolidated Statements Of Equity (unaudited) - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (loss)	Noncontrolling Interest
Common Stock, Shares, Outstanding at Dec. 31, 2017		53,579,986	39,064
Total equity at Dec. 31, 2017	$ 1,820,206	$ 53,580	$ (2,306)	$ 1,150,285	$ 548,617	$ (41,202)	$ 111,232
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	136,634				133,004		3,630
Other comprehensive income (loss), net of tax	1,260					1,260
Dividends on Common Stock	(25,444)				(25,444)
Share-based compensation, shares		64,770	14,895
Share-based compensation	755	$ 65	$ (743)	1,433
Dividend reinvestment and stock purchase plan, shares		4,061
Dividend reinvestment and stock purchase plan	219	$ 4		215
Other stock transactions	2				(16)	18
Distributions to noncontrolling interest	(5,648)						(5,648)
Common Stock, Shares, Outstanding at Mar. 31, 2018		53,648,817	53,959
Total equity at Mar. 31, 2018	1,927,984	$ 53,649	$ (3,049)	1,151,933	656,161	(39,924)	109,214
Common Stock, Shares, Outstanding at Dec. 31, 2017		53,579,986	39,064
Total equity at Dec. 31, 2017	1,820,206	$ 53,580	$ (2,306)	1,150,285	548,617	(41,202)	111,232
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss), net of tax	3,481
Common Stock, Shares, Outstanding at Sep. 30, 2018		53,661,863	72,915
Total equity at Sep. 30, 2018	1,921,179	$ 53,662	$ (4,072)	1,157,214	644,154	(37,703)	107,924
Common Stock, Shares, Outstanding at Mar. 31, 2018		53,648,817	53,959
Total equity at Mar. 31, 2018	1,927,984	$ 53,649	$ (3,049)	1,151,933	656,161	(39,924)	109,214
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	24,740				21,917		2,823
Other comprehensive income (loss), net of tax	1,161					1,161
Dividends on Common Stock	(25,435)				(25,435)
Share-based compensation, shares		13,033	11,022
Share-based compensation	2,439	$ 13	$ (593)	3,019
Other stock transactions	(6)			(5)	(1)
Distributions to noncontrolling interest	(4,350)						(4,350)
Common Stock, Shares, Outstanding at Jun. 30, 2018		53,661,850	64,981
Total equity at Jun. 30, 2018	1,926,533	$ 53,662	$ (3,642)	1,154,947	652,642	(38,763)	107,687
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	20,944				16,950		3,994
Other comprehensive income (loss), net of tax	1,060					1,060
Dividends on Common Stock	(25,430)				(25,430)
Share-based compensation, shares		13	7,934
Share-based compensation	1,677	$ 0	$ (430)	2,107
Dividend reinvestment and stock purchase plan	1			1
Other stock transactions	151			159	(8)
Distributions to noncontrolling interest	(3,757)						(3,757)
Common Stock, Shares, Outstanding at Sep. 30, 2018		53,661,863	72,915
Total equity at Sep. 30, 2018	1,921,179	$ 53,662	$ (4,072)	1,157,214	644,154	(37,703)	107,924
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), Including Portion Attributable to Nonredeemable Noncontrolling Interest	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	$ 60,378	$ (1,432)	1,469,410	777,262	(26,459)	104,543
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]
Other comprehensive income (loss), net of tax	1,221
Common Stock, Shares, Outstanding at Sep. 30, 2019		61,480,640	26,572
Total equity at Sep. 30, 2019	2,432,896	$ 61,481	$ (1,636)	1,553,190	742,138	(25,695)	103,418
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Implementation of ASU 2016-02 Leases	3,390				3,390
Common Stock, Shares, Outstanding at Mar. 31, 2019		60,378,020	23,756
Total equity at Mar. 31, 2019	2,383,702	$ 60,378	$ (1,432)	1,469,410	777,262	(26,459)	104,543
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	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)			(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	$ 61,091	$ (1,544)	1,522,208	761,222	(26,227)	103,248
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Implementation of ASU 2016-02 Leases	(3)				(3)
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	15,395				11,740		3,655
Other comprehensive income (loss), net of tax	532					532
Dividends on Common Stock	(30,827)				(30,827)
Share-based compensation, shares		18	1,213
Share-based compensation	1,677	$ 0	$ (92)	1,769
Issuance of common stock, shares		389,237
Issuance of common stock	30,001	$ 390		29,611
Issuance costs	(398)			(398)
Distributions to noncontrolling interest	(3,485)						(3,485)
Common Stock, Shares, Outstanding at Sep. 30, 2019		61,480,640	26,572
Total equity at Sep. 30, 2019	2,432,896	$ 61,481	$ (1,636)	$ 1,553,190	742,138	$ (25,695)	$ 103,418
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Implementation of ASU 2016-02 Leases	$ 3				$ 3

Condensed Consolidated Statem_6

Condensed Consolidated Statements Of Equity (unaudited) Condensed Consolidated Statements of Equity (unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.505	$ 0.505	$ 0.505	$ 0.475	$ 0.475	$ 0.475

Management's Statement_

Management's Statement:	9 Months Ended
	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Management's Statement	MANAGEMENT’S STATEMENT The unaudited Condensed Consolidated Financial Statements included herein have been prepared by Black Hills Corporation (together with our subsidiaries the “Company”, “us”, “we” or “our”), pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America have been condensed or omitted pursuant to such rules and regulations; however, we believe that the footnotes adequately disclose the information presented. These Condensed Consolidated Financial Statements should be read in conjunction with the consolidated financial statements and the notes thereto included in our 2018 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. Effective January 1, 2019, we changed our measure of segment performance to adjusted operating income, which impacted our segment disclosures for all periods presented. See Note 3 for more information. On November 1, 2017, the BHC board of directors approved a complete divestiture of our Oil and Gas segment. We completed the divestiture in 2018. The Oil and Gas segment assets and liabilities were classified as held for sale and the results of operations were shown in income (loss) from discontinued operations, except for certain general and administrative costs and interest expense which do not meet the criteria for income (loss) from discontinued operations. At the time the assets were classified as held for sale, depreciation, depletion and amortization expenses were no longer recorded. Unless otherwise noted, the amounts presented in the accompanying notes to the Condensed Consolidated Financial Statements relate to the Company’s continuing operations. See Note 17 and Note 21 for more information on discontinued operations. Use of Estimates and Basis of Presentation The information furnished in the accompanying Condensed Consolidated Financial Statements reflects certain estimates required and all adjustments, including accruals, which are, in the opinion of management, necessary for a fair presentation of the September 30, 2019 and December 31, 2018 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 nine months ended September 30, 2019 and September 30, 2018 , and our financial condition as of September 30, 2019 and December 31, 2018 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. Recently Issued Accounting Standards Simplifying the Test for Goodwill Impairment, 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. The new standard is effective for interim and annual reporting periods beginning after December 1, 2019, applied on a prospective basis with early adoption permitted. We do not anticipate the adoption of this guidance to have any impact on our financial position, results of operations or cash flows. Financial Instruments -- Credit Losses: Measurement of Credit Losses on Financial Instruments, ASU 2018-19 In June 2016, the FASB issued ASU 2016-13, Financial Instruments -- Credit Losses: Measurement of Credit Losses on Financial Instrument s, which was subsequently amended by ASU 2018-19 in November 2018. 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. It is effective for interim and annual reporting periods beginning after December 15, 2019, and will be applied on a modified-retrospective basis through a cumulative-effect adjustment to retained earnings as of January 1, 2020. We do not anticipate the adoption of this guidance to have a material impact on our financial position, results of operations or cash flows. Recently Adopted Accounting Standards Leases, ASU 2016-02 In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) to increase transparency and comparability among organizations by requiring the recognition of right-of-use assets and lease liabilities on the balance sheet for most leases, whereas previously only financing-type lease liabilities (capital leases) were recognized on the balance sheet. Under the new standard, disclosures are required to meet the objective of enabling users of financial statements to assess the amount, timing and uncertainty of cash flows arising from leases. We adopted the standard effective January 1, 2019. We elected not to recast comparative periods coinciding with the new lease standard transition and will report these comparative periods as presented under previous lease guidance. In addition, we elected the package of practical expedients permitted under the transition guidance with the new standard, which among other things, allowed us to carry forward the historical lease classification. We also elected the practical expedient related to land easements, allowing us to carry forward our accounting treatment for existing land easement agreements. Adoption of the new standard resulted in the recording of an operating lease right-of-use asset of $3.1 million , an operating lease obligation liability of $3.2 million , and an accrued rent receivable of $4.5 million , as of January 1, 2019 . The cumulative effect of the adoption, net of tax impact, was $3.4 million , which was recorded as an adjustment to retained earnings at January 1, 2019. Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities, ASU 2017-12 Effective January 1, 2019, we adopted ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. This standard better aligns risk management activities and financial reporting for hedging relationships, simplifies hedge accounting requirements and improves disclosures of hedging arrangements. The adoption of this guidance did not have a material impact on our financial position, results of operations or cash flows.

Revenue_

Revenue:	9 Months Ended
	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Revenue	REVENUE Revenue Recognition As of January 1, 2018, we adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , and its related amendments (collectively known as ASC 606). Revenue is recognized in an amount that reflects the consideration we expect to receive in exchange for goods or services, when control of the promised goods or services is transferred to our customers. 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 nine months ended September 30, 2019 and 2018 . Sales tax and other similar taxes are excluded from revenues. Three Months Ended September 30, 2019 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 162,214 $ 89,810 $ — $ 14,992 $ (8,146 ) $ 258,870 Transportation — 29,019 — — (195 ) 28,824 Wholesale 8,210 — 16,119 — (14,414 ) 9,915 Market - off-system sales 6,452 139 — — (1,488 ) 5,103 Transmission/Other 14,274 10,965 — — (4,206 ) 21,033 Revenue from contracts with customers $ 191,150 $ 129,933 $ 16,119 $ 14,992 $ (28,449 ) $ 323,745 Other revenues 234 811 9,692 560 (9,494 ) 1,803 Total revenues $ 191,384 $ 130,744 $ 25,811 $ 15,552 $ (37,943 ) $ 325,548 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 14,992 $ (8,146 ) $ 6,846 Services transferred over time 191,150 129,933 16,119 — (20,303 ) 316,899 Revenue from contracts with customers $ 191,150 $ 129,933 $ 16,119 $ 14,992 $ (28,449 ) $ 323,745 Three Months Ended September 30, 2018 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer Types: Retail $ 157,049 $ 88,559 $ — $ 16,751 $ (7,941 ) $ 254,418 Transportation — 30,079 — — (267 ) 29,812 Wholesale 8,255 — 15,373 — (13,935 ) 9,693 Market - off-system sales 9,059 140 — — (1,349 ) 7,850 Transmission/Other 10,196 11,887 — — (3,693 ) 18,390 Revenue from contracts with customers $ 184,559 $ 130,665 $ 15,373 $ 16,751 $ (27,185 ) $ 320,163 Other revenues 231 1,011 9,118 550 (9,094 ) 1,816 Total Revenues $ 184,790 $ 131,676 $ 24,491 $ 17,301 $ (36,279 ) $ 321,979 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 16,751 $ (7,942 ) $ 8,809 Services transferred over time 184,559 130,665 15,373 — (19,243 ) 311,354 Revenue from contracts with customers $ 184,559 $ 130,665 $ 15,373 $ 16,751 $ (27,185 ) $ 320,163 Nine Months Ended September 30, 2019 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 455,409 $ 567,715 $ — $ 43,249 $ (23,315 ) $ 1,043,058 Transportation — 102,159 — — (903 ) 101,256 Wholesale 23,334 — 46,650 — (40,923 ) 29,061 Market - off-system sales 16,592 517 — — (5,047 ) 12,062 Transmission/Other 42,865 35,767 — — (12,608 ) 66,024 Revenue from contracts with customers $ 538,200 $ 706,158 $ 46,650 $ 43,249 $ (82,796 ) $ 1,251,461 Other revenues 2,465 1,135 29,114 1,777 (28,706 ) 5,785 Total revenues $ 540,665 $ 707,293 $ 75,764 $ 45,026 $ (111,502 ) $ 1,257,246 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 43,249 $ (23,315 ) $ 19,934 Services transferred over time 538,200 706,158 46,650 — (59,481 ) 1,231,527 Revenue from contracts with customers $ 538,200 $ 706,158 $ 46,650 $ 43,249 $ (82,796 ) $ 1,251,461 Nine Months Ended September 30, 2018 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer Types: Retail $ 449,482 $ 565,816 $ — $ 49,653 $ (23,761 ) $ 1,041,190 Transportation — 100,760 — — (977 ) 99,783 Wholesale 25,497 — 43,744 — (39,457 ) 29,784 Market - off-system sales 18,142 728 — — (5,531 ) 13,339 Transmission/Other 36,622 36,230 — — (10,967 ) 61,885 Revenue from contracts with customers $ 529,743 $ 703,534 $ 43,744 $ 49,653 $ (80,693 ) $ 1,245,981 Other revenues 2,218 3,106 27,429 1,675 (27,337 ) 7,091 Total Revenues $ 531,961 $ 706,640 $ 71,173 $ 51,328 $ (108,030 ) $ 1,253,072 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 49,653 $ (23,761 ) $ 25,892 Services transferred over time 529,743 703,534 43,744 — (56,932 ) 1,220,089 Revenue from contracts with customers $ 529,743 $ 703,534 $ 43,744 $ 49,653 $ (80,693 ) $ 1,245,981 (a) Due to the changes in our segment disclosures discussed in Note 3, Power Generation Wholesale revenue was revised for the three and nine months ended September 30, 2018, which resulted in an increase of $0.9 million and $2.6 million , respectively. The changes to Power Generation Wholesale revenue were offset by changes to eliminations in Inter-company Revenues within Corporate and Other and there was no impact to our consolidated Total Revenues. 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. We do not typically incur costs that would be capitalized to obtain or fulfill a revenue contract.

Business Segment Information_

Business Segment Information:	9 Months Ended
	Sep. 30, 2019
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. Accounting standards for presentation of segments require an approach based on the way we organize the segments for making operating decisions and how the chief operating decision maker (CODM) assesses performance. Effective January 1, 2019, we concluded that adjusted operating income, instead of net income available for common stock which was used previously, is the most relevant metric for measuring segment performance. The change to our segment performance measure resulted in a revision of the Company’s segment disclosures for all periods to report adjusted operating income as the measure of segment performance. Prior to January 1, 2019, operating income for the Electric Utilities and Power Generation segments and Corporate and Other included the impacts of finance lease accounting relating to Colorado Electric’s PPA with Colorado IPP. This PPA provides 200 MW of energy and capacity to Colorado Electric from Colorado IPP’s combined-cycle turbines and expires on December 31, 2031. Finance lease accounting required us to de-recognize the asset from Colorado IPP (Power Generation segment), which legally owns the asset, and recognize it at Colorado Electric (Electric Utilities segment). The CODM assesses the performance of our segments using adjusted operating income, which recognizes intersegment revenues, costs, and assets for Colorado Electric’s PPA with Colorado IPP on an accrual basis rather than as a finance lease. Effective January 1, 2019, we changed how we account for this PPA at the segment level, which impacts disclosures for all periods for revenues, fuel and purchased power cost, operating income and total assets for the Electric Utilities and Power Generation segments as well as Corporate and Other. There were no revisions to Gas Utilities and Mining segments and this change had no effect on our consolidated revenues, fuel and purchased power cost, operating income or total assets. Segment information and Corporate and Other is as follows (in thousands): Three Months Ended September 30, 2019 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 185,811 $ 234 $ 5,339 $ — $ 191,384 Gas Utilities 129,385 810 549 — 130,744 Power Generation 1,703 531 14,415 9,162 25,811 Mining 6,846 228 8,146 332 15,552 Inter-company eliminations — — (28,449 ) (9,494 ) (37,943 ) Total $ 323,745 $ 1,803 $ — $ — $ 325,548 Three Months Ended September 30, 2018 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 179,527 $ 231 $ 5,032 $ — $ 184,790 Gas Utilities 130,390 1,011 275 — 131,676 Power Generation (a) 1,437 348 13,936 8,770 24,491 Mining 8,809 226 7,942 324 17,301 Inter-company eliminations (a) — — (27,185 ) (9,094 ) (36,279 ) Total $ 320,163 $ 1,816 $ — $ — $ 321,979 Nine Months Ended September 30, 2019 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 521,614 $ 2,465 $ 16,586 $ — $ 540,665 Gas Utilities 704,188 1,134 1,971 — 707,293 Power Generation 5,725 1,401 40,924 27,714 75,764 Mining 19,934 785 23,315 992 45,026 Inter-company eliminations — — (82,796 ) (28,706 ) (111,502 ) Total $ 1,251,461 $ 5,785 $ — $ — $ 1,257,246 Nine Months Ended September 30, 2018 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 513,270 $ 2,218 $ 16,473 $ — $ 531,961 Gas Utilities 702,532 3,106 1,002 — 706,640 Power Generation (a) 4,287 1,066 39,457 26,363 71,173 Mining 25,892 701 23,761 974 51,328 Inter-company eliminations (a) — — (80,693 ) (27,337 ) (108,030 ) Total $ 1,245,981 $ 7,091 $ — $ — $ 1,253,072 (a) Due to the changes in our segment disclosures, Power Generation Inter-company Operating Revenue for Contract Customers was revised for the three and nine months ended September 30, 2018 which resulted in an increase of $0.9 million and $2.6 million , respectively. The changes to Power Generation were offset by changes to Inter-company eliminations within Corporate and Other and there was no impact on our consolidated Total revenues. Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Adjusted operating income: Electric Utilities (a) $ 50,653 $ 43,393 $ 125,219 $ 123,073 Gas Utilities 4,736 4,240 116,607 116,168 Power Generation (a) 11,822 13,079 33,945 33,731 Mining 3,374 4,551 9,351 12,647 Corporate and Other (a) (34 ) (178 ) (439 ) (2,709 ) Operating income 70,551 65,085 284,683 282,910 Interest expense, net (33,487 ) (35,297 ) (102,469 ) (104,826 ) Impairment of investment (19,741 ) — (19,741 ) — Other income (expense), net 580 (510 ) 55 (1,923 ) Income tax benefit (expense) (b) (2,508 ) (7,477 ) (22,078 ) 11,784 Income from continuing operations 15,395 21,801 140,450 187,945 Net (loss) from discontinued operations — (857 ) — (5,627 ) Net income 15,395 20,944 140,450 182,318 Net income attributable to noncontrolling interest (3,655 ) (3,994 ) (10,319 ) (10,447 ) Net income available for common stock $ 11,740 $ 16,950 $ 130,131 $ 171,871 ___________ (a) Due to the changes in our segment disclosures, Adjusted operating income was revised for the three and nine months ended September 30, 2018, which resulted in an increase (decrease) as follows (in millions): Segment Three Months Ended September 30, 2018 Nine Months Ended September 30, 2018 Electric Utilities $ 1.6 $ 4.8 Power Generation (1.4 ) (4.4 ) Corporate and Other (0.2 ) (0.4 ) $ — $ — (b) Income tax benefit (expense) for the nine months ended September 30, 2018 included a $49 million tax benefit resulting from legal entity restructuring. See Note 18 for more information. Segment information and Corporate and Other balances included in the accompanying Condensed Consolidated Balance Sheets were as follows (in thousands): Total assets (net of inter-company eliminations) as of: September 30, 2019 December 31, 2018 Segment: Electric Utilities (a) $ 2,810,108 $ 2,707,695 Gas Utilities 3,797,941 3,623,475 Power Generation (a) 414,526 342,085 Mining 78,073 80,594 Corporate and Other 174,302 209,478 Total assets $ 7,274,950 $ 6,963,327 ___________ (a) Due to the changes in our segment disclosures, Electric Utilities and Power Generation Total assets were revised as of December 31, 2018 which resulted in an increase (decrease) of ($188) million and $188 million , respectively. There was no impact on our consolidated Total assets.

Accounts Receivable_

Accounts Receivable:	9 Months Ended
	Sep. 30, 2019
Receivables [Abstract]
Accounts Receivable	ACCOUNTS RECEIVABLE Following is a summary of Accounts receivable, net included in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: Accounts Unbilled Less Allowance for Accounts September 30, 2019 Receivable, Trade Revenue Doubtful Accounts Receivable, net Electric Utilities $ 39,151 $ 31,843 $ (500 ) $ 70,494 Gas Utilities 46,265 24,091 (2,490 ) 67,866 Power Generation 2,733 — — 2,733 Mining 1,804 — — 1,804 Corporate 6,261 — (169 ) 6,092 Total $ 96,214 $ 55,934 $ (3,159 ) $ 148,989 Accounts Unbilled Less Allowance for Accounts December 31, 2018 Receivable, Trade Revenue Doubtful Accounts Receivable, net Electric Utilities $ 39,721 $ 35,125 $ (448 ) $ 74,398 Gas Utilities 96,123 90,521 (2,592 ) 184,052 Power Generation 1,876 — — 1,876 Mining 3,988 — — 3,988 Corporate 5,008 — (169 ) 4,839 Total $ 146,716 $ 125,646 $ (3,209 ) $ 269,153

Regulatory Accounting_

Regulatory Accounting:	9 Months Ended
	Sep. 30, 2019
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Accounting	REGULATORY ACCOUNTING We had the following regulatory assets and liabilities (in thousands) as of: September 30, 2019 December 31, 2018 Regulatory assets Deferred energy and fuel cost adjustments (a) $ 31,832 $ 29,661 Deferred gas cost adjustments (a) 3,899 3,362 Gas price derivatives (a) 4,296 6,201 Deferred taxes on AFUDC (b) 7,691 7,841 Employee benefit plans (c) 107,921 110,524 Environmental (a) 917 959 Loss on reacquired debt (a) 19,710 21,001 Renewable energy standard adjustment (a) 2,871 1,722 Deferred taxes on flow through accounting (c) 37,609 31,044 Decommissioning costs (b) 11,206 11,700 Gas supply contract termination (a) 9,953 14,310 Other regulatory assets (a) 22,453 45,910 Total regulatory assets 260,358 284,235 Less current regulatory assets (46,206 ) (48,776 ) Regulatory assets, non-current $ 214,152 $ 235,459 Regulatory liabilities Deferred energy and gas costs (a) $ 9,919 $ 6,991 Employee benefit plan costs and related deferred taxes (c) 42,737 42,533 Cost of removal (a) 162,169 150,123 Excess deferred income taxes (c) 286,587 310,562 TCJA revenue reserve 2,770 18,032 Other regulatory liabilities (c) 19,759 12,553 Total regulatory liabilities 523,941 540,794 Less current regulatory liabilities (25,168 ) (29,810 ) Regulatory liabilities, non-current $ 498,773 $ 510,984 __________ (a) We are allowed 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 Matters 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 2018 Annual Report on Form 10-K. Regulatory Activity Wyoming Gas On June 13, 2019, we received approval from the WPSC to consolidate our Wyoming gas utility operations into a new utility entity. The Wyoming portion of Black Hills Gas Distribution, LLC, Cheyenne Light’s natural gas utility operations (Cheyenne Gas and Northeast Wyoming), and Wyoming Gas (Northwest Wyoming) were combined into a new company called Black Hills Wyoming Gas, LLC. On June 3, 2019, Wyoming Gas filed a rate review application with the WPSC to consolidate the rates, tariffs and services of its four existing gas distribution territories in Wyoming. The rate review requests $16 million in new revenue to recover investments in safety, reliability and system integrity. Wyoming Gas is also requesting a new rider mechanism to recover future safety and integrity investments in its system. A settlement was recently reached with the intervening parties in the rate review filing and filed with the WPSC on November 1, 2019. The stipulation and agreement are subject to review and approval by the WPSC, with a decision expected by the end of 2019. South Dakota Electric and Wyoming Electric South Dakota Electric and Wyoming Electric received approvals for the Renewable Ready Service Tariffs and related jointly-filed CPCN to construct the $57 million , 40 MW Corriedale Wind Energy Project. The wind project will be jointly owned by the two electric utilities to deliver renewable energy for large commercial, industrial and governmental agency customers. The project is expected to be in service by the end of 2020. In September 2019, the customer subscription period was completed with customer interest fulfilling the 40 MW of available energy. On November 1, 2019, South Dakota Electric filed with the SDPUC an amendment seeking approval to increase the generating capacity under the tariff for the South Dakota portion by 12.5 MW to a total of 32.5 MW. Nebraska On October 29, 2019, Nebraska Gas received approval from the NPSC to merge its two gas distribution companies in Nebraska. A rate review is expected to be filed by mid-year 2020 to consolidate the rates, tariffs and services of its two existing gas distribution companies. Kansas On June 25, 2019, Kansas Gas received approval from the Kansas Corporation Commission for an annual increase in revenue of $1.4 million , effective July 1, 2019, based on updates to the Gas System Reliability Surcharge Rider. Wyoming Electric On April 30, 2019, the WPSC approved Wyoming Electric’s application for a new Blockchain Interruptible Service Tariff. The utility has partnered with the economic development organization for City of Cheyenne and Laramie County to actively recruit blockchain customers to the state. This tariff is complementary to recently enacted Wyoming legislation supporting the development of blockchain within the state. Colorado On February 1, 2019, Colorado Gas filed a rate review with the CPUC requesting approval to consolidate rates, tariffs, and services of its two existing gas distribution territories in Colorado. The rate review requests $2.5 million in new revenue to recover investments in safety, reliability and system integrity. Colorado Gas is also requesting a new rider mechanism to recover future safety and integrity investments in its system. A decision from the CPUC is expected by March 2020.

Materials, Supplies and Fuel_

Materials, Supplies and Fuel:	9 Months Ended
	Sep. 30, 2019
Inventory, Net [Abstract]
Materials, Supplies and Fuel	MATERIALS, SUPPLIES AND FUEL The following amounts by major classification are included in Materials, supplies and fuel in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2019 December 31, 2018 Materials and supplies $ 81,382 $ 75,081 Fuel - Electric Utilities 2,535 2,850 Natural gas in storage held for distribution 39,085 39,368 Total materials, supplies and fuel $ 123,002 $ 117,299

Earnings Per Share_

Earnings Per Share:	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Earnings Per Share	EARNINGS PER SHARE A reconciliation of share amounts used to compute Earnings (loss) per share in the accompanying Condensed Consolidated Statements of Income was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Net income available for common stock $ 11,740 $ 16,950 $ 130,131 $ 171,871 Weighted average shares - basic 60,976 53,364 60,458 53,346 Dilutive effect of: Equity Units (a) — 1,344 — 1,060 Equity compensation 128 111 120 102 Weighted average shares - diluted 61,104 54,819 60,578 54,508 __________ (a) Calculated using the treasury stock method. On November 1, 2018, we completed settlement of the stock purchase contracts that were components of the Equity Units issued in November 2015. The following outstanding securities were excluded in the computation of diluted net income (loss) per share as their inclusion would have been anti-dilutive (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Equity compensation 2 12 4 15 Restricted Stock — — 1 — Anti-dilutive shares 2 12 5 15

Notes Payable, Current Maturiti

Notes Payable, Current Maturities and Debt:	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Notes Payable, Current Maturities and Debt	NOTES PAYABLE, CURRENT MATURITIES AND DEBT We had the following notes payable outstanding in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2019 December 31, 2018 Balance Outstanding Letters of Credit Balance Outstanding Letters of Credit Revolving Credit Facility $ 50,000 $ 18,313 $ — $ 22,311 CP Program 244,900 — 185,620 — Total $ 294,900 $ 18,313 $ 185,620 $ 22,311 Our $750 million corporate Revolving Credit Facility extends through July 30, 2023 with two , one year extension options (subject to consent from lenders). This facility includes an accordion feature that allows us, with the consent of the administrative agent, the issuing agents and each bank increasing or providing a new commitment, to increase total commitments up to $1.0 billion . Borrowings continue to be available under a base rate or various Eurodollar rate options. The interest costs associated with the letters of credit or borrowings and the commitment fee under the Revolving Credit Facility are determined based upon our Corporate credit rating from S&P, Fitch, and Moody's for our senior unsecured long-term debt. Based on our credit ratings, the margins for base rate borrowings, Eurodollar borrowings, and letters of credit were 0.125% , 1.125% , and 1.125% , respectively, at September 30, 2019 . Based on our credit ratings, a 0.175% commitment fee was charged on the unused amount at September 30, 2019 . We have a $750 million , unsecured CP Program that is backstopped by the Revolving Credit Facility. Amounts outstanding under the Revolving Credit Facility and the CP Program, either individually or in the aggregate, cannot exceed $750 million . The notes issued under the CP Program may have maturities not to exceed 397 days from the date of issuance and bear interest (or are sold at par less a discount representing an interest factor) based on, among other things, the size and maturity date of the note, the frequency of the issuance and our credit ratings. Under the CP Program, any borrowings rank equally with our unsecured debt. Notes under the CP Program are not registered and are offered and issued pursuant to a registration exemption. Our net short-term borrowings (payments) during the nine months ended September 30, 2019 were $109 million . At September 30, 2019 , the weighted average interest rate on short-term borrowings was 2.43% . Debt Covenants Under our Revolving Credit Facility and term loan agreements, we are required to maintain a Consolidated Indebtedness to Capitalization Ratio not to exceed 0.65 to 1.00 . Our Consolidated Indebtedness to Capitalization Ratio was calculated by dividing (i) Consolidated Indebtedness, which includes letters of credit and certain guarantees issued, by (ii) Capital, which includes Consolidated Indebtedness plus Net Worth, which excludes noncontrolling interest in subsidiaries. As of September 30, 2019 , we were in compliance with these covenants. Debt Transaction On June 17, 2019, we amended our Corporate term loan due July 30, 2020. This amendment increased total commitments to $400 million from $300 million , extended the term through June 17, 2021, and had substantially similar terms and covenants as the amended and restated Revolving Credit Facility. The net proceeds from the increase in total commitments were used to pay down short-term debt. Proceeds from the October 3, 2019 public debt offering were used to repay this term loan. Subsequent Event - Debt Offering On October 3, 2019, we completed a public debt offering of $700 million principal amount in senior unsecured notes. The debt offering consisted of $400 million of 3.05% 10-year senior notes due October 15, 2029 and $300 million of 3.875% 30-year senior notes due October 15, 2049 (together the “Notes”). The proceeds of the Notes were used for the following: • Repay the $400 million Corporate term loan under the Amended and Restated Credit Agreement due June 17, 2021; • Retire the $200 million 5.875% senior notes due July 15, 2020; and • Repay a portion of short-term debt.

Equity_

Equity:	9 Months Ended
	Sep. 30, 2019
Statement of Stockholders' Equity [Abstract]
Equity	EQUITY At-the-Market Equity Offering Program Our ATM equity offering program allows us to sell shares of our common stock with an aggregate value of up to $300 million . The shares may be offered from time to time pursuant to a sales agreement dated August 4, 2017. Shares of common stock are offered pursuant to our shelf registration statement filed with the SEC. During the three months ended September 30, 2019, we issued a total of 389,237 shares of common stock under the ATM equity offering program for proceeds of $30 million , net of $0.3 million in commissions. During the nine months ended September 30, 2019, we issued a total of 1,328,332 shares of common stock under the ATM equity offering program for proceeds of $99 million , net of $1.0 million in commissions. As of September 30, 2019 , there were no shares that were sold, but not settled.

Risk Management Activities_

Risk Management Activities:	9 Months Ended
	Sep. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Risk Management Activities	RISK MANAGEMENT ACTIVITIES Our activities in the regulated and non-regulated energy sectors expose us to a number of risks in the normal operation of our businesses. Depending on the activity, we are exposed to varying degrees of market risk and credit risk. To manage and mitigate these identified risks, we have adopted the Black Hills Corporation Risk and Credit Policies and Procedures as discussed in our 2018 Annual Report on Form 10-K. Market Risk Market risk is the potential loss that might occur as a result of an adverse change in market price or rate. We are exposed to, but not limited to, commodity price risk associated with our retail natural gas marketing activities and our fuel procurement for certain gas-fired generation assets. Credit Risk Credit risk is the risk of financial loss resulting from non-performance of contractual obligations by a counterparty. For other than retail utility 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 guaranties, prepayments, 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 customer’s current creditworthiness, as determined by review of their current credit information. We maintain a provision for estimated credit losses based upon historical experience and any specific customer collection issue that is identified. Our derivative and hedging activities recorded 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 11 . Utilities The operations of our utilities, including natural gas sold by our Gas Utilities and 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), 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 state 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 risks using over-the-counter and exchange traded options and swaps with counterparties in anticipation of forecasted purchases and/or sales during time frames ranging from October 2019 through October 2021; a portion of these swaps have been designated as cash flow hedges to mitigate the commodity price risk associated with forward contracts to deliver gas to our Choice Gas Program customers. The gain or loss on these designated derivatives is reported in AOCI in the accompanying Condensed Consolidated Balance Sheets. Effectiveness of our hedged position is evaluated at inception of the hedge, upon occurrence of a triggering event and as of the end of each quarter. The contract or notional amounts and terms of the natural gas derivative commodity instruments held at our utilities are composed of both long and short positions. We were in a net long position as of: September 30, 2019 December 31, 2018 Notional (MMBtus) Maximum Term (months) (a) Notional (MMBtus) Maximum Term (months) (a) Natural gas futures purchased 2,350,000 15 4,000,000 24 Natural gas options purchased, net 8,580,000 6 4,320,000 13 Natural gas basis swaps purchased 2,090,000 15 3,960,000 24 Natural gas over-the-counter swaps, net (b) 5,460,000 25 3,660,000 24 Natural gas physical contracts, net (c) 23,459,639 6 18,325,852 30 __________ (a) Term reflects the maximum forward period hedged. (b) As of September 30, 2019 , 1,812,500 MMBtus were designated as cash flow hedges. (c) Volumes exclude contracts that qualify for the normal purchase, normal sales exception. Based on September 30, 2019 prices, a $0.4 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. We have certain derivative contracts which contain credit provisions. These credit provisions may require the Company to post collateral when credit exposure to the Company is in excess of a negotiated line of unsecured credit. At September 30, 2019 , the Company posted $0.5 million related to such provisions, which is included in Other current assets on the Condensed Consolidated Balance Sheets. Cash Flow Hedges The impacts of cash flow hedges on our Condensed Consolidated Statements of Income is presented below for the three and nine months ended September 30, 2019 and 2018 . Note that this presentation does not reflect gains or losses arising from the underlying physical transactions; therefore, it is not indicative of the economic profit or loss we realized when the underlying physical and financial transactions were settled. Three Months Ended September 30, 2019 (in thousands) Derivatives in Cash Flow Hedging Relationships Location of Reclassifications from AOCI into Income Amount of Gain/(Loss) Reclassified from AOCI into Income Interest rate swaps Interest expense $ (713 ) Commodity derivatives Fuel, purchased power and cost of natural gas sold (129 ) Total $ (842 ) Three Months Ended September 30, 2018 (in thousands) Derivatives in Cash Flow Hedging Relationships Location of Reclassifications from AOCI into Income Amount of Gain/(Loss) Reclassified from AOCI into Income Interest rate swaps Interest expense $ (712 ) Commodity derivatives Fuel, purchased power and cost of natural gas sold (18 ) Total $ (730 ) Nine Months Ended September 30, 2019 (in thousands) Derivatives in Cash Flow Hedging Relationships Location of Reclassifications from AOCI into Income Amount of Gain/(Loss) Reclassified from AOCI into Income Interest rate swaps Interest expense $ (2,139 ) Commodity derivatives Fuel, purchased power and cost of natural gas sold 508 Total $ (1,631 ) Nine Months Ended September 30, 2018 (in thousands) Derivatives in Cash Flow Hedging Relationships Location of Reclassifications from AOCI into Income Amount of Gain/(Loss) Reclassified from AOCI into Income Interest rate swaps Interest expense $ (2,138 ) Commodity derivatives Fuel, purchased power and cost of natural gas sold (802 ) Total $ (2,940 ) The following tables summarize the gains and losses arising from hedging transactions that were recognized as a component of other comprehensive income (loss) for the three and nine months ended September 30, 2019 and 2018 . Three Months Ended September 30, 2019 2018 (in thousands) Increase (decrease) in fair value: Forward commodity contracts $ (150 ) $ 30 Recognition of (gains) losses in earnings due to settlements: Interest rate swaps 713 712 Forward commodity contracts 129 18 Total other comprehensive income (loss) from hedging $ 692 $ 760 Nine Months Ended September 30, 2019 2018 (in thousands) Increase (decrease) in fair value: Forward commodity contracts $ (434 ) $ (219 ) Recognition of (gains) losses in earnings due to settlements: Interest rate swaps 2,139 2,138 Forward commodity contracts (508 ) 802 Total other comprehensive income (loss) from hedging $ 1,197 $ 2,721 Derivatives Not Designated as Hedge Instruments The following table summarizes the impacts of derivative instruments not designated as hedge instruments on our Condensed Consolidated Statements of Income for the three and nine months ended September 30, 2019 and 2018 (in thousands). Note that this presentation does not reflect gains or losses arising from the underlying physical transactions; therefore, it is not indicative of the economic profit or loss we realized when the underlying physical and financial transactions were settled. Three Months Ended September 30, 2019 2018 Derivatives Not Designated as Hedging Instruments Location of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income Commodity derivatives Fuel, purchased power and cost of natural gas sold $ (20 ) $ (96 ) Commodity derivatives Other income (expense), net 142 — $ 122 $ (96 ) Nine Months Ended September 30, 2019 2018 Derivatives Not Designated as Hedging Instruments Location of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income Commodity derivatives Fuel, purchased power and cost of natural gas sold $ (1,180 ) $ 929 Commodity derivatives Other income (expense), net $ 142 $ — $ (1,038 ) $ 929 As discussed above, financial instruments used in our regulated utilities are not designated as cash flow hedges. However, there is no earnings impact because the unrealized gains and losses arising from the use of these financial instruments are recorded as Regulatory assets or Regulatory liabilities. The net unrealized losses included in our Regulatory asset or Regulatory liability accounts related to the hedges in our utilities were $4.3 million and $6.2 million as of September 30, 2019 and December 31, 2018 , respectively.

Fair Value Measurements_

Fair Value Measurements:	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Derivative Financial Instruments The accounting guidance for fair value measurements requires certain disclosures about assets and liabilities measured at fair value. This guidance establishes a hierarchical framework for disclosing the observability of the inputs utilized in measuring assets and liabilities at fair value. 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. For additional information, see Notes 1, 9, 10 and 11 to the Consolidated Financial Statements included in our 2018 Annual Report on Form 10-K filed with the SEC. 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. Valuation Methodologies for Derivatives The commodity contracts for our Utilities Segments, are valued using the market approach and include exchange-traded futures, options, basis swaps and over-the-counter swaps and options (Level 2) for 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. 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 21. Recurring Fair Value Measurements As of September 30, 2019 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting Total (in thousands) Assets: Commodity derivatives — Utilities $ — $ 2,750 $ — $ (2,335 ) $ 415 Total $ — $ 2,750 $ — $ (2,335 ) $ 415 Liabilities: Commodity derivatives — Utilities $ — $ 6,080 $ — $ (3,471 ) $ 2,609 Total $ — $ 6,080 $ — $ (3,471 ) $ 2,609 As of December 31, 2018 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting Total (in thousands) Assets: Commodity derivatives — Utilities $ — $ 2,927 $ — $ (1,408 ) $ 1,519 Total $ — $ 2,927 $ — $ (1,408 ) $ 1,519 Liabilities: Commodity derivatives — Utilities $ — $ 6,801 $ — $ (5,794 ) $ 1,007 Total $ — $ 6,801 $ — $ (5,794 ) $ 1,007 Fair Value Measures 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 permitted in accordance with accounting standards for offsetting and under terms of our master netting agreements and the impact of legally enforceable 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 September 30, 2019 December 31, 2018 Derivatives designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets — current $ — $ 415 Noncurrent commodity derivatives Other assets, non-current 2 18 Liability derivative instruments: Current commodity derivatives Derivative liabilities — current (427 ) (114 ) Noncurrent commodity derivatives Other deferred credits and other liabilities (70 ) (4 ) Total derivatives designated as hedges $ (495 ) $ 315 Derivatives not designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets — current $ 412 $ 1,085 Noncurrent commodity derivatives Other assets, non-current 1 1 Liability derivative instruments: Current commodity derivatives Derivative liabilities — current (1,969 ) (833 ) Noncurrent commodity derivatives Other deferred credits and other liabilities (143 ) (56 ) Total derivatives not designated as hedges $ (1,699 ) $ 197 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 2018 Annual Report on Form 10-K.

Fair Value of Financial Instrum

Fair Value of Financial Instruments:	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	FAIR VALUE OF FINANCIAL INSTRUMENTS Other financial instruments for which the carrying value did not equal fair value were as follows (in thousands) as of: September 30, 2019 December 31, 2018 Carrying Amount Fair Value Carrying Amount Fair Value Long-term debt, including current maturities (a) (b) $ 3,054,978 $ 3,424,747 $ 2,956,578 $ 3,039,108 __________ (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 in Level 2 in the fair value hierarchy. (b) Carrying amount of long-term debt is net of deferred financing costs.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss):	9 Months Ended
	Sep. 30, 2019
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 Nine Months Ended September 30, 2019 September 30, 2018 September 30, 2019 September 30, 2018 Gains and (losses) on cash flow hedges: Interest rate swaps Interest expense $ (713 ) $ (712 ) $ (2,139 ) $ (2,138 ) Commodity contracts Fuel, purchased power and cost of natural gas sold (129 ) (18 ) 508 (802 ) (842 ) (730 ) (1,631 ) (2,940 ) Income tax Income tax benefit (expense) 170 149 358 643 Total reclassification adjustments related to cash flow hedges, net of tax $ (672 ) $ (581 ) $ (1,273 ) $ (2,297 ) Amortization of components of defined benefit plans: Prior service cost Operations and maintenance $ 20 $ 44 $ 59 $ 133 Actuarial gain (loss) Operations and maintenance (84 ) (621 ) (525 ) (1,865 ) (64 ) (577 ) (466 ) (1,732 ) Income tax Income tax benefit (expense) 89 128 184 380 Total reclassification adjustments related to defined benefit plans, net of tax $ 25 $ (449 ) $ (282 ) $ (1,352 ) Total reclassifications $ (647 ) $ (1,030 ) $ (1,555 ) $ (3,649 ) 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, 2018 $ (17,307 ) $ 328 $ (9,937 ) $ (26,916 ) Other comprehensive income (loss) before reclassifications — (334 ) — (334 ) Amounts reclassified from AOCI 1,639 (366 ) 282 1,555 As of September 30, 2019 $ (15,668 ) $ (372 ) $ (9,655 ) $ (25,695 ) Interest Rate Swaps Commodity Derivatives Employee Benefit Plans Total As of December 31, 2017 $ (19,581 ) $ (518 ) $ (21,103 ) $ (41,202 ) Other comprehensive income (loss) before reclassifications — (168 ) — (168 ) Amounts reclassified from AOCI 1,682 615 1,352 3,649 Reclassifications of certain tax effects from AOCI 15 — 3 18 As of September 30, 2018 $ (17,884 ) $ (71 ) $ (19,748 ) $ (37,703 )

Supplemental Disclosure of Cash

Supplemental Disclosure of Cash Flow Information:	9 Months Ended
	Sep. 30, 2019
Supplemental Cash Flow Information [Abstract]
Supplemental Disclosure of Cash Flow Information	SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION Nine Months Ended September 30, 2019 September 30, 2018 (in thousands) Non-cash investing and financing activities — Property, plant and equipment acquired with accrued liabilities $ 86,661 $ 49,631 Cash (paid) refunded during the period — Interest (net of amounts capitalized) $ (99,375 ) $ (104,035 ) Income taxes $ 2,255 $ (14,842 )

Employee Benefit Plans_

Employee Benefit Plans:	9 Months Ended
	Sep. 30, 2019
Defined Benefit Plan [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS Defined Benefit Pension Plan The components of net periodic benefit cost for the Defined Benefit Pension Plan were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Service cost $ 1,346 $ 1,708 $ 4,037 $ 5,125 Interest cost 4,344 3,867 13,031 11,602 Expected return on plan assets (6,100 ) (6,185 ) (18,300 ) (18,555 ) Prior service cost 6 15 19 44 Net loss (gain) 941 2,158 2,822 6,473 Net periodic benefit cost $ 537 $ 1,563 $ 1,609 $ 4,689 Defined Benefit Postretirement Healthcare Plans The components of net periodic benefit cost for the Defined Benefit Postretirement Healthcare Plans were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Service cost $ 454 $ 573 $ 1,362 $ 1,718 Interest cost 560 521 1,683 1,563 Expected return on plan assets (57 ) (57 ) (172 ) (170 ) Prior service cost (benefit) (99 ) (99 ) (298 ) (297 ) Net loss (gain) — 54 — 162 Net periodic benefit cost $ 858 $ 992 $ 2,575 $ 2,976 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans The components of net periodic benefit cost for the Supplemental Non-qualified Defined Benefit and Defined Contribution Plans were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Service cost $ 429 $ 632 $ 2,406 $ 1,347 Interest cost 324 293 972 878 Prior service cost — — 1 1 Net loss (gain) 134 250 402 750 Net periodic benefit cost $ 887 $ 1,175 $ 3,781 $ 2,976 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 2019 and anticipated contributions for 2019 and 2020 are as follows (in thousands): Contributions Made Contributions Made Additional Contributions Contributions Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Anticipated for 2019 Anticipated for 2020 Defined Benefit Pension Plan $ 12,700 $ 12,700 $ — $ 12,700 Non-pension Defined Benefit Postretirement Healthcare Plans $ 1,109 $ 3,326 $ 1,109 $ 4,815 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans $ 366 $ 1,098 $ 366 $ 1,406

Commitments and Contingencies_

Commitments and Contingencies:	9 Months Ended
	Sep. 30, 2019
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 2018 Annual Report on Form 10-K except for those described below. Future Purchase Agreement - Related Party On August 2, 2019, Black Hills Wyoming and Wyoming Electric filed a request with FERC for approval of a new 60 MW PPA. If approved, Black Hills Wyoming will continue to deliver 60 MW of energy to Wyoming Electric from its Wygen I power plant starting January 1, 2023, and continuing for 20 additional years. A decision from FERC is pending. Platte River Power Authority PPAs • On June 26, 2019, Colorado Electric entered into a PPA with Platte River Power Authority to purchase up to 60 MW of wind energy upon construction completion of a new wind project, which is expected in mid-2020. This agreement will expire May 31, 2030. • On June 26, 2019, Colorado Electric entered into a PPA with Platte River Power Authority to purchase 25 MW of unit contingent energy. This agreement was effective September 1, 2019 and will expire June 30, 2024. The following is a schedule of unconditional purchase obligations required under the 25 MW Platte River Power Authority PPA as of September 30, 2019 (in thousands): 2019 $ 1,369 2020 $ 5,475 2021 $ 5,475 2022 $ 5,475 2023 $ 5,475 Thereafter $ 2,738

Discontinued Operations_

Discontinued Operations:	9 Months Ended
	Sep. 30, 2019
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations	DISCONTINUED OPERATIONS Results of operations for discontinued operations were classified as Loss from discontinued operations, net of income taxes in the accompanying Condensed Consolidated Statements of Income. Prior periods relating to our discontinued operations were also reclassified to reflect consistency within our condensed consolidated financial statements. Oil and Gas Segment On November 1, 2017, the BHC Board of Directors approved a complete divestiture of our Oil and Gas segment. We completed the divestiture in 2018. See Note 21 for more information.

Income Taxes_

Income Taxes:	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES Income tax benefit (expense) for the Three Months Ended September 30, 2019 Compared to the Three Months Ended September 30, 2018 . Income tax benefit (expense) for the three months ended September 30, 2019 was $(2.5) million compared to $(7.5) million reported for the same period in 2018 . The decrease in tax expense was primarily due to a prior year $(5.3) million income tax expense associated with changes in the previously estimated impact of tax reform on deferred income taxes. For the three months ended September 30, 2019 the effective tax rate was 14.0% compared to 7.6% excluding the tax reform adjustments, for the same period in 2018. The higher effective tax rate is primarily due to a prior year state tax benefit. Income tax benefit (expense) for the Nine Months Ended September 30, 2019 Compared to the Nine Months Ended September 30, 2018 . Income tax benefit (expense) for the nine months ended September 30, 2019 was $(22) million compared to $12 million reported for the same period in 2018 . The increase in tax expense was primarily due to a prior year $49 million tax benefit resulting from legal entity restructuring partially offset by a prior year $(7.5) million income tax expense associated with changes in the previously estimated impact of tax reform on deferred income taxes. For the nine months ended September 30, 2019 the effective tax rate was 13.6% compared to 17.1% excluding the legal entity restructuring and tax reform adjustments, for the same period in 2018. The lower effective tax rate is primarily due to $5.0 million of federal production tax credits and related state investment tax credits associated with new wind assets and a $1.0 million tax benefit for deferred tax amortization related to tax reform.

Accrued Liabilities_

Accrued Liabilities:	9 Months Ended
	Sep. 30, 2019
Payables and Accruals [Abstract]
Accrued Liabilities	ACCRUED LIABILITIES The following amounts by major classification are included in Accrued liabilities in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2019 December 31, 2018 Accrued employee compensation, benefits and withholdings $ 57,313 $ 63,742 Accrued property taxes 38,937 42,510 Customer deposits and prepayments 56,220 43,574 Accrued interest and contract adjustment payments 35,100 31,759 Other (none of which is individually significant) 30,262 33,916 Total accrued liabilities $ 217,832 $ 215,501

Leases_

Leases:	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Leases	LEASES Lessee We lease from third parties certain office and operation center facilities, communication tower sites, equipment, and materials storage. Our leases have remaining terms ranging from less than one year to 37 years , including options to extend that are reasonably certain to be exercised. The components of lease expense were as follows (in thousands): Income Statement Location Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Operating lease cost Operations and maintenance $ 380 $ 1,076 Finance lease cost: Amortization of right-of-use asset Depreciation, depletion and amortization 28 72 Interest on lease liabilities Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) 5 14 Total lease cost $ 413 $ 1,162 Supplemental balance sheet information related to leases was as follows (in thousands): Balance Sheet Location As of September 30, 2019 Assets: Operating lease assets Other assets, non-current $ 4,864 Finance lease assets Other assets, non-current 493 Total lease assets $ 5,357 Liabilities: Current: Operating leases Accrued liabilities $ 970 Finance lease Accrued liabilities 80 Noncurrent: Operating leases Other deferred credits and other liabilities 4,252 Finance lease Other deferred credits and other liabilities 419 Total lease liabilities $ 5,721 Supplemental cash flow information related to leases was as follows (in thousands): Nine Months Ended September 30, 2019 Cash paid included in the measurement of lease liabilities: Operating cash flows from operating leases $ 895 Operating cash flows from finance lease $ 14 Financing cash flows from finance lease $ 66 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ 2,775 Finance lease $ 67 As of September 30, 2019 Weighted average remaining lease term (years): Operating leases 8 years Finance lease 4 years Weighted average discount rate: Operating leases 4.27 % Finance lease 4.19 % As of September 30, 2019 , scheduled maturities of lease liabilities for future years were as follows (in thousands): Operating Leases Finance Lease Total 2019 (a) $ 368 $ 32 $ 400 2020 992 126 1,118 2021 855 126 981 2022 736 126 862 2023 714 126 840 Thereafter 2,682 10 2,692 Total lease payments (b) $ 6,347 $ 546 $ 6,893 Less imputed interest 1,125 47 1,172 Present value of lease liabilities $ 5,222 $ 499 $ 5,721 (a) Includes lease liabilities for the remaining three months of 2019 . (b) Lease payments exclude payments to landlords for common area maintenance, real estate taxes, and insurance. As previously disclosed in Note 14 of the Notes to the Consolidated Financial Statements in our 2018 Annual Report on Form 10-K, prior to the adoption of ASU 2016-02, Leases (Topic 842), the future minimum payments required under operating lease agreements as of December 31, 2018 were as follows (in thousands): Operating Leases 2019 $ 1,052 2020 464 2021 344 2022 224 2023 216 Thereafter 1,776 Total lease payments $ 4,076
Leases	LEASES Lessee We lease from third parties certain office and operation center facilities, communication tower sites, equipment, and materials storage. Our leases have remaining terms ranging from less than one year to 37 years , including options to extend that are reasonably certain to be exercised. The components of lease expense were as follows (in thousands): Income Statement Location Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Operating lease cost Operations and maintenance $ 380 $ 1,076 Finance lease cost: Amortization of right-of-use asset Depreciation, depletion and amortization 28 72 Interest on lease liabilities Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) 5 14 Total lease cost $ 413 $ 1,162 Supplemental balance sheet information related to leases was as follows (in thousands): Balance Sheet Location As of September 30, 2019 Assets: Operating lease assets Other assets, non-current $ 4,864 Finance lease assets Other assets, non-current 493 Total lease assets $ 5,357 Liabilities: Current: Operating leases Accrued liabilities $ 970 Finance lease Accrued liabilities 80 Noncurrent: Operating leases Other deferred credits and other liabilities 4,252 Finance lease Other deferred credits and other liabilities 419 Total lease liabilities $ 5,721 Supplemental cash flow information related to leases was as follows (in thousands): Nine Months Ended September 30, 2019 Cash paid included in the measurement of lease liabilities: Operating cash flows from operating leases $ 895 Operating cash flows from finance lease $ 14 Financing cash flows from finance lease $ 66 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ 2,775 Finance lease $ 67 As of September 30, 2019 Weighted average remaining lease term (years): Operating leases 8 years Finance lease 4 years Weighted average discount rate: Operating leases 4.27 % Finance lease 4.19 % As of September 30, 2019 , scheduled maturities of lease liabilities for future years were as follows (in thousands): Operating Leases Finance Lease Total 2019 (a) $ 368 $ 32 $ 400 2020 992 126 1,118 2021 855 126 981 2022 736 126 862 2023 714 126 840 Thereafter 2,682 10 2,692 Total lease payments (b) $ 6,347 $ 546 $ 6,893 Less imputed interest 1,125 47 1,172 Present value of lease liabilities $ 5,222 $ 499 $ 5,721 (a) Includes lease liabilities for the remaining three months of 2019 . (b) Lease payments exclude payments to landlords for common area maintenance, real estate taxes, and insurance. As previously disclosed in Note 14 of the Notes to the Consolidated Financial Statements in our 2018 Annual Report on Form 10-K, prior to the adoption of ASU 2016-02, Leases (Topic 842), the future minimum payments required under operating lease agreements as of December 31, 2018 were as follows (in thousands): Operating Leases 2019 $ 1,052 2020 464 2021 344 2022 224 2023 216 Thereafter 1,776 Total lease payments $ 4,076
Leases	LEASES Lessee We lease from third parties certain office and operation center facilities, communication tower sites, equipment, and materials storage. Our leases have remaining terms ranging from less than one year to 37 years , including options to extend that are reasonably certain to be exercised. The components of lease expense were as follows (in thousands): Income Statement Location Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Operating lease cost Operations and maintenance $ 380 $ 1,076 Finance lease cost: Amortization of right-of-use asset Depreciation, depletion and amortization 28 72 Interest on lease liabilities Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) 5 14 Total lease cost $ 413 $ 1,162 Supplemental balance sheet information related to leases was as follows (in thousands): Balance Sheet Location As of September 30, 2019 Assets: Operating lease assets Other assets, non-current $ 4,864 Finance lease assets Other assets, non-current 493 Total lease assets $ 5,357 Liabilities: Current: Operating leases Accrued liabilities $ 970 Finance lease Accrued liabilities 80 Noncurrent: Operating leases Other deferred credits and other liabilities 4,252 Finance lease Other deferred credits and other liabilities 419 Total lease liabilities $ 5,721 Supplemental cash flow information related to leases was as follows (in thousands): Nine Months Ended September 30, 2019 Cash paid included in the measurement of lease liabilities: Operating cash flows from operating leases $ 895 Operating cash flows from finance lease $ 14 Financing cash flows from finance lease $ 66 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ 2,775 Finance lease $ 67 As of September 30, 2019 Weighted average remaining lease term (years): Operating leases 8 years Finance lease 4 years Weighted average discount rate: Operating leases 4.27 % Finance lease 4.19 % As of September 30, 2019 , scheduled maturities of lease liabilities for future years were as follows (in thousands): Operating Leases Finance Lease Total 2019 (a) $ 368 $ 32 $ 400 2020 992 126 1,118 2021 855 126 981 2022 736 126 862 2023 714 126 840 Thereafter 2,682 10 2,692 Total lease payments (b) $ 6,347 $ 546 $ 6,893 Less imputed interest 1,125 47 1,172 Present value of lease liabilities $ 5,222 $ 499 $ 5,721 (a) Includes lease liabilities for the remaining three months of 2019 . (b) Lease payments exclude payments to landlords for common area maintenance, real estate taxes, and insurance. As previously disclosed in Note 14 of the Notes to the Consolidated Financial Statements in our 2018 Annual Report on Form 10-K, prior to the adoption of ASU 2016-02, Leases (Topic 842), the future minimum payments required under operating lease agreements as of December 31, 2018 were as follows (in thousands): Operating Leases 2019 $ 1,052 2020 464 2021 344 2022 224 2023 216 Thereafter 1,776 Total lease payments $ 4,076 Lessor We lease to third parties certain generating station ground leases, communication tower sites, and a natural gas pipeline. These leases have remaining terms ranging from less than one year to 35 years . The components of lease revenue were as follows (in thousands): Income Statement Location Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Operating lease income Revenue $ 544 $ 1,749 As of September 30, 2019 , scheduled maturities of lease receivables for future years were as follows (in thousands): Operating Leases 2019 (a) $ 551 2020 2,035 2021 1,857 2022 1,793 2023 1,799 Thereafter 55,481 Total lease receivables $ 63,516 (a) Includes lease receivables for the remaining three months of 2019 .

Investments_

Investments:	9 Months Ended
	Sep. 30, 2019
Investments, All Other Investments [Abstract]
Investments	INVESTMENTS In February 2018, we made a contribution of $28 million of assets in exchange for equity securities in a privately held oil and gas company as we divested from 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 and nine months ended September 30, 2019, which was the difference between the carrying amount and the fair value of the investment. The following table presents the carrying value of our investments (in thousands) as of: September 30, 2019 December 31, 2018 Investment in privately held oil and gas company $ 8,359 $ 28,100 Cash surrender value of life insurance contracts 12,907 12,812 Other investments 317 101 Total investments $ 21,583 $ 41,013

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2019
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS There are no subsequent events, other than those disclosed in Note 8.

Management's Statement (Policie

Management's Statement (Policies)	9 Months Ended
	Sep. 30, 2019
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. Effective January 1, 2019, we changed our measure of segment performance to adjusted operating income, which impacted our segment disclosures for all periods presented. See Note 3 for more information. On November 1, 2017, the BHC board of directors approved a complete divestiture of our Oil and Gas segment. We completed the divestiture in 2018. The Oil and Gas segment assets and liabilities were classified as held for sale and the results of operations were shown in income (loss) from discontinued operations, except for certain general and administrative costs and interest expense which do not meet the criteria for income (loss) from discontinued operations. At the time the assets were classified as held for sale, depreciation, depletion and amortization expenses were no longer recorded. Unless otherwise noted, the amounts presented in the accompanying notes to the Condensed Consolidated Financial Statements relate to the Company’s continuing operations. See Note 17 and Note 21 for more information on discontinued operations.
Use of Estimates and Basis of Presentation	Use of Estimates and Basis of Presentation The information furnished in the accompanying Condensed Consolidated Financial Statements reflects certain estimates required and all adjustments, including accruals, which are, in the opinion of management, necessary for a fair presentation of the September 30, 2019 and December 31, 2018 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 nine months ended September 30, 2019 and September 30, 2018 , and our financial condition as of September 30, 2019 and December 31, 2018 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.
Recently Issued and Adopted Accounting Standards	Recently Issued Accounting Standards Simplifying the Test for Goodwill Impairment, 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. The new standard is effective for interim and annual reporting periods beginning after December 1, 2019, applied on a prospective basis with early adoption permitted. We do not anticipate the adoption of this guidance to have any impact on our financial position, results of operations or cash flows. Financial Instruments -- Credit Losses: Measurement of Credit Losses on Financial Instruments, ASU 2018-19 In June 2016, the FASB issued ASU 2016-13, Financial Instruments -- Credit Losses: Measurement of Credit Losses on Financial Instrument s, which was subsequently amended by ASU 2018-19 in November 2018. 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. It is effective for interim and annual reporting periods beginning after December 15, 2019, and will be applied on a modified-retrospective basis through a cumulative-effect adjustment to retained earnings as of January 1, 2020. We do not anticipate the adoption of this guidance to have a material impact on our financial position, results of operations or cash flows. Recently Adopted Accounting Standards Leases, ASU 2016-02 In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) to increase transparency and comparability among organizations by requiring the recognition of right-of-use assets and lease liabilities on the balance sheet for most leases, whereas previously only financing-type lease liabilities (capital leases) were recognized on the balance sheet. Under the new standard, disclosures are required to meet the objective of enabling users of financial statements to assess the amount, timing and uncertainty of cash flows arising from leases. We adopted the standard effective January 1, 2019. We elected not to recast comparative periods coinciding with the new lease standard transition and will report these comparative periods as presented under previous lease guidance. In addition, we elected the package of practical expedients permitted under the transition guidance with the new standard, which among other things, allowed us to carry forward the historical lease classification. We also elected the practical expedient related to land easements, allowing us to carry forward our accounting treatment for existing land easement agreements. Adoption of the new standard resulted in the recording of an operating lease right-of-use asset of $3.1 million , an operating lease obligation liability of $3.2 million , and an accrued rent receivable of $4.5 million , as of January 1, 2019 . The cumulative effect of the adoption, net of tax impact, was $3.4 million , which was recorded as an adjustment to retained earnings at January 1, 2019. Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities, ASU 2017-12 Effective January 1, 2019, we adopted ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. This standard better aligns risk management activities and financial reporting for hedging relationships, simplifies hedge accounting requirements and improves disclosures of hedging arrangements. The adoption of this guidance did not have a material impact on our financial position, results of operations or cash flows.
Revenue Recognition	Revenue Recognition As of January 1, 2018, we adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , and its related amendments (collectively known as ASC 606). Revenue is recognized in an amount that reflects the consideration we expect to receive in exchange for goods or services, when control of the promised goods or services is transferred to our customers. 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 nine months ended September 30, 2019 and 2018 . Sales tax and other similar taxes are excluded from revenues. Three Months Ended September 30, 2019 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 162,214 $ 89,810 $ — $ 14,992 $ (8,146 ) $ 258,870 Transportation — 29,019 — — (195 ) 28,824 Wholesale 8,210 — 16,119 — (14,414 ) 9,915 Market - off-system sales 6,452 139 — — (1,488 ) 5,103 Transmission/Other 14,274 10,965 — — (4,206 ) 21,033 Revenue from contracts with customers $ 191,150 $ 129,933 $ 16,119 $ 14,992 $ (28,449 ) $ 323,745 Other revenues 234 811 9,692 560 (9,494 ) 1,803 Total revenues $ 191,384 $ 130,744 $ 25,811 $ 15,552 $ (37,943 ) $ 325,548 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 14,992 $ (8,146 ) $ 6,846 Services transferred over time 191,150 129,933 16,119 — (20,303 ) 316,899 Revenue from contracts with customers $ 191,150 $ 129,933 $ 16,119 $ 14,992 $ (28,449 ) $ 323,745 Three Months Ended September 30, 2018 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer Types: Retail $ 157,049 $ 88,559 $ — $ 16,751 $ (7,941 ) $ 254,418 Transportation — 30,079 — — (267 ) 29,812 Wholesale 8,255 — 15,373 — (13,935 ) 9,693 Market - off-system sales 9,059 140 — — (1,349 ) 7,850 Transmission/Other 10,196 11,887 — — (3,693 ) 18,390 Revenue from contracts with customers $ 184,559 $ 130,665 $ 15,373 $ 16,751 $ (27,185 ) $ 320,163 Other revenues 231 1,011 9,118 550 (9,094 ) 1,816 Total Revenues $ 184,790 $ 131,676 $ 24,491 $ 17,301 $ (36,279 ) $ 321,979 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 16,751 $ (7,942 ) $ 8,809 Services transferred over time 184,559 130,665 15,373 — (19,243 ) 311,354 Revenue from contracts with customers $ 184,559 $ 130,665 $ 15,373 $ 16,751 $ (27,185 ) $ 320,163 Nine Months Ended September 30, 2019 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 455,409 $ 567,715 $ — $ 43,249 $ (23,315 ) $ 1,043,058 Transportation — 102,159 — — (903 ) 101,256 Wholesale 23,334 — 46,650 — (40,923 ) 29,061 Market - off-system sales 16,592 517 — — (5,047 ) 12,062 Transmission/Other 42,865 35,767 — — (12,608 ) 66,024 Revenue from contracts with customers $ 538,200 $ 706,158 $ 46,650 $ 43,249 $ (82,796 ) $ 1,251,461 Other revenues 2,465 1,135 29,114 1,777 (28,706 ) 5,785 Total revenues $ 540,665 $ 707,293 $ 75,764 $ 45,026 $ (111,502 ) $ 1,257,246 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 43,249 $ (23,315 ) $ 19,934 Services transferred over time 538,200 706,158 46,650 — (59,481 ) 1,231,527 Revenue from contracts with customers $ 538,200 $ 706,158 $ 46,650 $ 43,249 $ (82,796 ) $ 1,251,461 Nine Months Ended September 30, 2018 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer Types: Retail $ 449,482 $ 565,816 $ — $ 49,653 $ (23,761 ) $ 1,041,190 Transportation — 100,760 — — (977 ) 99,783 Wholesale 25,497 — 43,744 — (39,457 ) 29,784 Market - off-system sales 18,142 728 — — (5,531 ) 13,339 Transmission/Other 36,622 36,230 — — (10,967 ) 61,885 Revenue from contracts with customers $ 529,743 $ 703,534 $ 43,744 $ 49,653 $ (80,693 ) $ 1,245,981 Other revenues 2,218 3,106 27,429 1,675 (27,337 ) 7,091 Total Revenues $ 531,961 $ 706,640 $ 71,173 $ 51,328 $ (108,030 ) $ 1,253,072 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 49,653 $ (23,761 ) $ 25,892 Services transferred over time 529,743 703,534 43,744 — (56,932 ) 1,220,089 Revenue from contracts with customers $ 529,743 $ 703,534 $ 43,744 $ 49,653 $ (80,693 ) $ 1,245,981 (a) Due to the changes in our segment disclosures discussed in Note 3, Power Generation Wholesale revenue was revised for the three and nine months ended September 30, 2018, which resulted in an increase of $0.9 million and $2.6 million , respectively. The changes to Power Generation Wholesale revenue were offset by changes to eliminations in Inter-company Revenues within Corporate and Other and there was no impact to our consolidated Total Revenues. 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. We do not typically incur costs that would be capitalized to obtain or fulfill a revenue contract.

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2019
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 nine months ended September 30, 2019 and 2018 . Sales tax and other similar taxes are excluded from revenues. Three Months Ended September 30, 2019 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 162,214 $ 89,810 $ — $ 14,992 $ (8,146 ) $ 258,870 Transportation — 29,019 — — (195 ) 28,824 Wholesale 8,210 — 16,119 — (14,414 ) 9,915 Market - off-system sales 6,452 139 — — (1,488 ) 5,103 Transmission/Other 14,274 10,965 — — (4,206 ) 21,033 Revenue from contracts with customers $ 191,150 $ 129,933 $ 16,119 $ 14,992 $ (28,449 ) $ 323,745 Other revenues 234 811 9,692 560 (9,494 ) 1,803 Total revenues $ 191,384 $ 130,744 $ 25,811 $ 15,552 $ (37,943 ) $ 325,548 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 14,992 $ (8,146 ) $ 6,846 Services transferred over time 191,150 129,933 16,119 — (20,303 ) 316,899 Revenue from contracts with customers $ 191,150 $ 129,933 $ 16,119 $ 14,992 $ (28,449 ) $ 323,745 Three Months Ended September 30, 2018 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer Types: Retail $ 157,049 $ 88,559 $ — $ 16,751 $ (7,941 ) $ 254,418 Transportation — 30,079 — — (267 ) 29,812 Wholesale 8,255 — 15,373 — (13,935 ) 9,693 Market - off-system sales 9,059 140 — — (1,349 ) 7,850 Transmission/Other 10,196 11,887 — — (3,693 ) 18,390 Revenue from contracts with customers $ 184,559 $ 130,665 $ 15,373 $ 16,751 $ (27,185 ) $ 320,163 Other revenues 231 1,011 9,118 550 (9,094 ) 1,816 Total Revenues $ 184,790 $ 131,676 $ 24,491 $ 17,301 $ (36,279 ) $ 321,979 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 16,751 $ (7,942 ) $ 8,809 Services transferred over time 184,559 130,665 15,373 — (19,243 ) 311,354 Revenue from contracts with customers $ 184,559 $ 130,665 $ 15,373 $ 16,751 $ (27,185 ) $ 320,163 Nine Months Ended September 30, 2019 Electric Utilities Gas Utilities Power Generation Mining Inter-company Revenues Total Customer types: (in thousands) Retail $ 455,409 $ 567,715 $ — $ 43,249 $ (23,315 ) $ 1,043,058 Transportation — 102,159 — — (903 ) 101,256 Wholesale 23,334 — 46,650 — (40,923 ) 29,061 Market - off-system sales 16,592 517 — — (5,047 ) 12,062 Transmission/Other 42,865 35,767 — — (12,608 ) 66,024 Revenue from contracts with customers $ 538,200 $ 706,158 $ 46,650 $ 43,249 $ (82,796 ) $ 1,251,461 Other revenues 2,465 1,135 29,114 1,777 (28,706 ) 5,785 Total revenues $ 540,665 $ 707,293 $ 75,764 $ 45,026 $ (111,502 ) $ 1,257,246 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 43,249 $ (23,315 ) $ 19,934 Services transferred over time 538,200 706,158 46,650 — (59,481 ) 1,231,527 Revenue from contracts with customers $ 538,200 $ 706,158 $ 46,650 $ 43,249 $ (82,796 ) $ 1,251,461 Nine Months Ended September 30, 2018 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer Types: Retail $ 449,482 $ 565,816 $ — $ 49,653 $ (23,761 ) $ 1,041,190 Transportation — 100,760 — — (977 ) 99,783 Wholesale 25,497 — 43,744 — (39,457 ) 29,784 Market - off-system sales 18,142 728 — — (5,531 ) 13,339 Transmission/Other 36,622 36,230 — — (10,967 ) 61,885 Revenue from contracts with customers $ 529,743 $ 703,534 $ 43,744 $ 49,653 $ (80,693 ) $ 1,245,981 Other revenues 2,218 3,106 27,429 1,675 (27,337 ) 7,091 Total Revenues $ 531,961 $ 706,640 $ 71,173 $ 51,328 $ (108,030 ) $ 1,253,072 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 49,653 $ (23,761 ) $ 25,892 Services transferred over time 529,743 703,534 43,744 — (56,932 ) 1,220,089 Revenue from contracts with customers $ 529,743 $ 703,534 $ 43,744 $ 49,653 $ (80,693 ) $ 1,245,981 (a) Due to the changes in our segment disclosures discussed in Note 3, Power Generation Wholesale revenue was revised for the three and nine months ended September 30, 2018, which resulted in an increase of $0.9 million and $2.6 million , respectively. The changes to Power Generation Wholesale revenue were offset by changes to eliminations in Inter-company Revenues within Corporate and Other and there was no impact to our consolidated Total Revenues.

Business Segment Information (T

Business Segment Information (Tables)	9 Months Ended
	Sep. 30, 2019
Segment Reporting Information, Additional Information [Abstract]
Segment Reporting	Segment information and Corporate and Other is as follows (in thousands): Three Months Ended September 30, 2019 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 185,811 $ 234 $ 5,339 $ — $ 191,384 Gas Utilities 129,385 810 549 — 130,744 Power Generation 1,703 531 14,415 9,162 25,811 Mining 6,846 228 8,146 332 15,552 Inter-company eliminations — — (28,449 ) (9,494 ) (37,943 ) Total $ 323,745 $ 1,803 $ — $ — $ 325,548 Three Months Ended September 30, 2018 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 179,527 $ 231 $ 5,032 $ — $ 184,790 Gas Utilities 130,390 1,011 275 — 131,676 Power Generation (a) 1,437 348 13,936 8,770 24,491 Mining 8,809 226 7,942 324 17,301 Inter-company eliminations (a) — — (27,185 ) (9,094 ) (36,279 ) Total $ 320,163 $ 1,816 $ — $ — $ 321,979 Nine Months Ended September 30, 2019 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 521,614 $ 2,465 $ 16,586 $ — $ 540,665 Gas Utilities 704,188 1,134 1,971 — 707,293 Power Generation 5,725 1,401 40,924 27,714 75,764 Mining 19,934 785 23,315 992 45,026 Inter-company eliminations — — (82,796 ) (28,706 ) (111,502 ) Total $ 1,251,461 $ 5,785 $ — $ — $ 1,257,246 Nine Months Ended September 30, 2018 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 513,270 $ 2,218 $ 16,473 $ — $ 531,961 Gas Utilities 702,532 3,106 1,002 — 706,640 Power Generation (a) 4,287 1,066 39,457 26,363 71,173 Mining 25,892 701 23,761 974 51,328 Inter-company eliminations (a) — — (80,693 ) (27,337 ) (108,030 ) Total $ 1,245,981 $ 7,091 $ — $ — $ 1,253,072 (a) Due to the changes in our segment disclosures, Power Generation Inter-company Operating Revenue for Contract Customers was revised for the three and nine months ended September 30, 2018 which resulted in an increase of $0.9 million and $2.6 million , respectively. The changes to Power Generation were offset by changes to Inter-company eliminations within Corporate and Other and there was no impact on our consolidated Total revenues. Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Adjusted operating income: Electric Utilities (a) $ 50,653 $ 43,393 $ 125,219 $ 123,073 Gas Utilities 4,736 4,240 116,607 116,168 Power Generation (a) 11,822 13,079 33,945 33,731 Mining 3,374 4,551 9,351 12,647 Corporate and Other (a) (34 ) (178 ) (439 ) (2,709 ) Operating income 70,551 65,085 284,683 282,910 Interest expense, net (33,487 ) (35,297 ) (102,469 ) (104,826 ) Impairment of investment (19,741 ) — (19,741 ) — Other income (expense), net 580 (510 ) 55 (1,923 ) Income tax benefit (expense) (b) (2,508 ) (7,477 ) (22,078 ) 11,784 Income from continuing operations 15,395 21,801 140,450 187,945 Net (loss) from discontinued operations — (857 ) — (5,627 ) Net income 15,395 20,944 140,450 182,318 Net income attributable to noncontrolling interest (3,655 ) (3,994 ) (10,319 ) (10,447 ) Net income available for common stock $ 11,740 $ 16,950 $ 130,131 $ 171,871 ___________ (a) Due to the changes in our segment disclosures, Adjusted operating income was revised for the three and nine months ended September 30, 2018, which resulted in an increase (decrease) as follows (in millions): Segment Three Months Ended September 30, 2018 Nine Months Ended September 30, 2018 Electric Utilities $ 1.6 $ 4.8 Power Generation (1.4 ) (4.4 ) Corporate and Other (0.2 ) (0.4 ) $ — $ — (b) Income tax benefit (expense) for the nine months ended September 30, 2018 included a $49 million tax benefit resulting from legal entity restructuring. See Note 18 for more information.
Reconciliation of Assets from Segment to Consolidated	Segment information and Corporate and Other balances included in the accompanying Condensed Consolidated Balance Sheets were as follows (in thousands): Total assets (net of inter-company eliminations) as of: September 30, 2019 December 31, 2018 Segment: Electric Utilities (a) $ 2,810,108 $ 2,707,695 Gas Utilities 3,797,941 3,623,475 Power Generation (a) 414,526 342,085 Mining 78,073 80,594 Corporate and Other 174,302 209,478 Total assets $ 7,274,950 $ 6,963,327 ___________ (a) Due to the changes in our segment disclosures, Electric Utilities and Power Generation Total assets were revised as of December 31, 2018 which resulted in an increase (decrease) of ($188) million and $188 million , respectively. There was no impact on our consolidated Total assets.

Accounts Receivable (Tables)

Accounts Receivable (Tables)	9 Months Ended
	Sep. 30, 2019
Receivables [Abstract]
Accounts Receivable and Allowance for Doubtful Accounts	Following is a summary of Accounts receivable, net included in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: Accounts Unbilled Less Allowance for Accounts September 30, 2019 Receivable, Trade Revenue Doubtful Accounts Receivable, net Electric Utilities $ 39,151 $ 31,843 $ (500 ) $ 70,494 Gas Utilities 46,265 24,091 (2,490 ) 67,866 Power Generation 2,733 — — 2,733 Mining 1,804 — — 1,804 Corporate 6,261 — (169 ) 6,092 Total $ 96,214 $ 55,934 $ (3,159 ) $ 148,989 Accounts Unbilled Less Allowance for Accounts December 31, 2018 Receivable, Trade Revenue Doubtful Accounts Receivable, net Electric Utilities $ 39,721 $ 35,125 $ (448 ) $ 74,398 Gas Utilities 96,123 90,521 (2,592 ) 184,052 Power Generation 1,876 — — 1,876 Mining 3,988 — — 3,988 Corporate 5,008 — (169 ) 4,839 Total $ 146,716 $ 125,646 $ (3,209 ) $ 269,153

Regulatory Accounting (Tables)

Regulatory Accounting (Tables)	9 Months Ended
	Sep. 30, 2019
Regulatory Assets and Liabilities Disclosure [Abstract]
Schedule of Regulatory Assets and Liabilities	We had the following regulatory assets and liabilities (in thousands) as of: September 30, 2019 December 31, 2018 Regulatory assets Deferred energy and fuel cost adjustments (a) $ 31,832 $ 29,661 Deferred gas cost adjustments (a) 3,899 3,362 Gas price derivatives (a) 4,296 6,201 Deferred taxes on AFUDC (b) 7,691 7,841 Employee benefit plans (c) 107,921 110,524 Environmental (a) 917 959 Loss on reacquired debt (a) 19,710 21,001 Renewable energy standard adjustment (a) 2,871 1,722 Deferred taxes on flow through accounting (c) 37,609 31,044 Decommissioning costs (b) 11,206 11,700 Gas supply contract termination (a) 9,953 14,310 Other regulatory assets (a) 22,453 45,910 Total regulatory assets 260,358 284,235 Less current regulatory assets (46,206 ) (48,776 ) Regulatory assets, non-current $ 214,152 $ 235,459 Regulatory liabilities Deferred energy and gas costs (a) $ 9,919 $ 6,991 Employee benefit plan costs and related deferred taxes (c) 42,737 42,533 Cost of removal (a) 162,169 150,123 Excess deferred income taxes (c) 286,587 310,562 TCJA revenue reserve 2,770 18,032 Other regulatory liabilities (c) 19,759 12,553 Total regulatory liabilities 523,941 540,794 Less current regulatory liabilities (25,168 ) (29,810 ) Regulatory liabilities, non-current $ 498,773 $ 510,984 __________ (a) We are allowed 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.

Materials, Supplies and Fuel (T

Materials, Supplies and Fuel (Tables)	9 Months Ended
	Sep. 30, 2019
Inventory, Net [Abstract]
Materials, Supplies and Fuel	The following amounts by major classification are included in Materials, supplies and fuel in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2019 December 31, 2018 Materials and supplies $ 81,382 $ 75,081 Fuel - Electric Utilities 2,535 2,850 Natural gas in storage held for distribution 39,085 39,368 Total materials, supplies and fuel $ 123,002 $ 117,299

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Schedule of Earnings Per Share Reconciliation	A reconciliation of share amounts used to compute Earnings (loss) per share in the accompanying Condensed Consolidated Statements of Income was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Net income available for common stock $ 11,740 $ 16,950 $ 130,131 $ 171,871 Weighted average shares - basic 60,976 53,364 60,458 53,346 Dilutive effect of: Equity Units (a) — 1,344 — 1,060 Equity compensation 128 111 120 102 Weighted average shares - diluted 61,104 54,819 60,578 54,508 __________ (a) Calculated using the treasury stock method. On November 1, 2018, we completed settlement of the stock purchase contracts that were components of the Equity Units issued in November 2015.
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following outstanding securities were excluded in the computation of diluted net income (loss) per share as their inclusion would have been anti-dilutive (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Equity compensation 2 12 4 15 Restricted Stock — — 1 — Anti-dilutive shares 2 12 5 15

Notes Payable, Current Maturi_2

Notes Payable, Current Maturities and Debt (Tables)	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Schedule of Short-term Debt	We had the following notes payable outstanding in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2019 December 31, 2018 Balance Outstanding Letters of Credit Balance Outstanding Letters of Credit Revolving Credit Facility $ 50,000 $ 18,313 $ — $ 22,311 CP Program 244,900 — 185,620 — Total $ 294,900 $ 18,313 $ 185,620 $ 22,311

Risk Management Activities (Tab

Risk Management Activities (Tables)	9 Months Ended
	Sep. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Contract or notional amounts and terms of marketing activities and derivative commodity instruments	The contract or notional amounts and terms of the natural gas derivative commodity instruments held at our utilities are composed of both long and short positions. We were in a net long position as of: September 30, 2019 December 31, 2018 Notional (MMBtus) Maximum Term (months) (a) Notional (MMBtus) Maximum Term (months) (a) Natural gas futures purchased 2,350,000 15 4,000,000 24 Natural gas options purchased, net 8,580,000 6 4,320,000 13 Natural gas basis swaps purchased 2,090,000 15 3,960,000 24 Natural gas over-the-counter swaps, net (b) 5,460,000 25 3,660,000 24 Natural gas physical contracts, net (c) 23,459,639 6 18,325,852 30 __________ (a) Term reflects the maximum forward period hedged. (b) As of September 30, 2019 , 1,812,500 MMBtus were designated as cash flow hedges. (c) Volumes exclude contracts that qualify for the normal purchase, normal sales exception.
Derivative Instruments, Gain (Loss)	The impacts of cash flow hedges on our Condensed Consolidated Statements of Income is presented below for the three and nine months ended September 30, 2019 and 2018 . Note that this presentation does not reflect gains or losses arising from the underlying physical transactions; therefore, it is not indicative of the economic profit or loss we realized when the underlying physical and financial transactions were settled. Three Months Ended September 30, 2019 (in thousands) Derivatives in Cash Flow Hedging Relationships Location of Reclassifications from AOCI into Income Amount of Gain/(Loss) Reclassified from AOCI into Income Interest rate swaps Interest expense $ (713 ) Commodity derivatives Fuel, purchased power and cost of natural gas sold (129 ) Total $ (842 ) Three Months Ended September 30, 2018 (in thousands) Derivatives in Cash Flow Hedging Relationships Location of Reclassifications from AOCI into Income Amount of Gain/(Loss) Reclassified from AOCI into Income Interest rate swaps Interest expense $ (712 ) Commodity derivatives Fuel, purchased power and cost of natural gas sold (18 ) Total $ (730 ) Nine Months Ended September 30, 2019 (in thousands) Derivatives in Cash Flow Hedging Relationships Location of Reclassifications from AOCI into Income Amount of Gain/(Loss) Reclassified from AOCI into Income Interest rate swaps Interest expense $ (2,139 ) Commodity derivatives Fuel, purchased power and cost of natural gas sold 508 Total $ (1,631 ) Nine Months Ended September 30, 2018 (in thousands) Derivatives in Cash Flow Hedging Relationships Location of Reclassifications from AOCI into Income Amount of Gain/(Loss) Reclassified from AOCI into Income Interest rate swaps Interest expense $ (2,138 ) Commodity derivatives Fuel, purchased power and cost of natural gas sold (802 ) Total $ (2,940 ) The following tables summarize the gains and losses arising from hedging transactions that were recognized as a component of other comprehensive income (loss) for the three and nine months ended September 30, 2019 and 2018 . Three Months Ended September 30, 2019 2018 (in thousands) Increase (decrease) in fair value: Forward commodity contracts $ (150 ) $ 30 Recognition of (gains) losses in earnings due to settlements: Interest rate swaps 713 712 Forward commodity contracts 129 18 Total other comprehensive income (loss) from hedging $ 692 $ 760 Nine Months Ended September 30, 2019 2018 (in thousands) Increase (decrease) in fair value: Forward commodity contracts $ (434 ) $ (219 ) Recognition of (gains) losses in earnings due to settlements: Interest rate swaps 2,139 2,138 Forward commodity contracts (508 ) 802 Total other comprehensive income (loss) from hedging $ 1,197 $ 2,721 Derivatives Not Designated as Hedge Instruments The following table summarizes the impacts of derivative instruments not designated as hedge instruments on our Condensed Consolidated Statements of Income for the three and nine months ended September 30, 2019 and 2018 (in thousands). Note that this presentation does not reflect gains or losses arising from the underlying physical transactions; therefore, it is not indicative of the economic profit or loss we realized when the underlying physical and financial transactions were settled. Three Months Ended September 30, 2019 2018 Derivatives Not Designated as Hedging Instruments Location of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income Commodity derivatives Fuel, purchased power and cost of natural gas sold $ (20 ) $ (96 ) Commodity derivatives Other income (expense), net 142 — $ 122 $ (96 ) Nine Months Ended September 30, 2019 2018 Derivatives Not Designated as Hedging Instruments Location of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income Amount of Gain/(Loss) on Derivatives Recognized in Income Commodity derivatives Fuel, purchased power and cost of natural gas sold $ (1,180 ) $ 929 Commodity derivatives Other income (expense), net $ 142 $ — $ (1,038 ) $ 929 As discussed above, financial instruments used in our regulated utilities are not designated as cash flow hedges. However, there is no earnings impact because the unrealized gains and losses arising from the use of these financial instruments are recorded as Regulatory assets or Regulatory liabilities. The net unrealized losses included in our Regulatory asset or Regulatory liability accounts related to the hedges in our utilities were $4.3 million and $6.2 million as of September 30, 2019 and December 31, 2018 , respectively.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Schedule of Fair Value Hierarchy, Measured on Recurring Basis	Recurring Fair Value Measurements As of September 30, 2019 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting Total (in thousands) Assets: Commodity derivatives — Utilities $ — $ 2,750 $ — $ (2,335 ) $ 415 Total $ — $ 2,750 $ — $ (2,335 ) $ 415 Liabilities: Commodity derivatives — Utilities $ — $ 6,080 $ — $ (3,471 ) $ 2,609 Total $ — $ 6,080 $ — $ (3,471 ) $ 2,609 As of December 31, 2018 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting Total (in thousands) Assets: Commodity derivatives — Utilities $ — $ 2,927 $ — $ (1,408 ) $ 1,519 Total $ — $ 2,927 $ — $ (1,408 ) $ 1,519 Liabilities: Commodity derivatives — Utilities $ — $ 6,801 $ — $ (5,794 ) $ 1,007 Total $ — $ 6,801 $ — $ (5,794 ) $ 1,007
Schedule of Derivative Instruments Balance Sheet Location	The following table presents the fair value and balance sheet classification of our derivative instruments (in thousands) as of: Balance Sheet Location September 30, 2019 December 31, 2018 Derivatives designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets — current $ — $ 415 Noncurrent commodity derivatives Other assets, non-current 2 18 Liability derivative instruments: Current commodity derivatives Derivative liabilities — current (427 ) (114 ) Noncurrent commodity derivatives Other deferred credits and other liabilities (70 ) (4 ) Total derivatives designated as hedges $ (495 ) $ 315 Derivatives not designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets — current $ 412 $ 1,085 Noncurrent commodity derivatives Other assets, non-current 1 1 Liability derivative instruments: Current commodity derivatives Derivative liabilities — current (1,969 ) (833 ) Noncurrent commodity derivatives Other deferred credits and other liabilities (143 ) (56 ) Total derivatives not designated as hedges $ (1,699 ) $ 197

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Other financial instruments for which the carrying value did not equal fair value were as follows (in thousands) as of: September 30, 2019 December 31, 2018 Carrying Amount Fair Value Carrying Amount Fair Value Long-term debt, including current maturities (a) (b) $ 3,054,978 $ 3,424,747 $ 2,956,578 $ 3,039,108 __________ (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 in Level 2 in the fair value hierarchy. (b) Carrying amount of long-term debt is net of deferred financing costs.

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2019
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 Nine Months Ended September 30, 2019 September 30, 2018 September 30, 2019 September 30, 2018 Gains and (losses) on cash flow hedges: Interest rate swaps Interest expense $ (713 ) $ (712 ) $ (2,139 ) $ (2,138 ) Commodity contracts Fuel, purchased power and cost of natural gas sold (129 ) (18 ) 508 (802 ) (842 ) (730 ) (1,631 ) (2,940 ) Income tax Income tax benefit (expense) 170 149 358 643 Total reclassification adjustments related to cash flow hedges, net of tax $ (672 ) $ (581 ) $ (1,273 ) $ (2,297 ) Amortization of components of defined benefit plans: Prior service cost Operations and maintenance $ 20 $ 44 $ 59 $ 133 Actuarial gain (loss) Operations and maintenance (84 ) (621 ) (525 ) (1,865 ) (64 ) (577 ) (466 ) (1,732 ) Income tax Income tax benefit (expense) 89 128 184 380 Total reclassification adjustments related to defined benefit plans, net of tax $ 25 $ (449 ) $ (282 ) $ (1,352 ) Total reclassifications $ (647 ) $ (1,030 ) $ (1,555 ) $ (3,649 )
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, 2018 $ (17,307 ) $ 328 $ (9,937 ) $ (26,916 ) Other comprehensive income (loss) before reclassifications — (334 ) — (334 ) Amounts reclassified from AOCI 1,639 (366 ) 282 1,555 As of September 30, 2019 $ (15,668 ) $ (372 ) $ (9,655 ) $ (25,695 ) Interest Rate Swaps Commodity Derivatives Employee Benefit Plans Total As of December 31, 2017 $ (19,581 ) $ (518 ) $ (21,103 ) $ (41,202 ) Other comprehensive income (loss) before reclassifications — (168 ) — (168 ) Amounts reclassified from AOCI 1,682 615 1,352 3,649 Reclassifications of certain tax effects from AOCI 15 — 3 18 As of September 30, 2018 $ (17,884 ) $ (71 ) $ (19,748 ) $ (37,703 )

Supplemental Disclosure of Ca_2

Supplemental Disclosure of Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2019
Supplemental Cash Flow Information [Abstract]
Supplemental Disclosure of Cash Flow Information	Nine Months Ended September 30, 2019 September 30, 2018 (in thousands) Non-cash investing and financing activities — Property, plant and equipment acquired with accrued liabilities $ 86,661 $ 49,631 Cash (paid) refunded during the period — Interest (net of amounts capitalized) $ (99,375 ) $ (104,035 ) Income taxes $ 2,255 $ (14,842 )

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2019
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 September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Service cost $ 1,346 $ 1,708 $ 4,037 $ 5,125 Interest cost 4,344 3,867 13,031 11,602 Expected return on plan assets (6,100 ) (6,185 ) (18,300 ) (18,555 ) Prior service cost 6 15 19 44 Net loss (gain) 941 2,158 2,822 6,473 Net periodic benefit cost $ 537 $ 1,563 $ 1,609 $ 4,689 Defined Benefit Postretirement Healthcare Plans The components of net periodic benefit cost for the Defined Benefit Postretirement Healthcare Plans were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Service cost $ 454 $ 573 $ 1,362 $ 1,718 Interest cost 560 521 1,683 1,563 Expected return on plan assets (57 ) (57 ) (172 ) (170 ) Prior service cost (benefit) (99 ) (99 ) (298 ) (297 ) Net loss (gain) — 54 — 162 Net periodic benefit cost $ 858 $ 992 $ 2,575 $ 2,976 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans The components of net periodic benefit cost for the Supplemental Non-qualified Defined Benefit and Defined Contribution Plans were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Service cost $ 429 $ 632 $ 2,406 $ 1,347 Interest cost 324 293 972 878 Prior service cost — — 1 1 Net loss (gain) 134 250 402 750 Net periodic benefit cost $ 887 $ 1,175 $ 3,781 $ 2,976
Schedule of Defined Benefit Plans Contributions	Contributions made in 2019 and anticipated contributions for 2019 and 2020 are as follows (in thousands): Contributions Made Contributions Made Additional Contributions Contributions Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Anticipated for 2019 Anticipated for 2020 Defined Benefit Pension Plan $ 12,700 $ 12,700 $ — $ 12,700 Non-pension Defined Benefit Postretirement Healthcare Plans $ 1,109 $ 3,326 $ 1,109 $ 4,815 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans $ 366 $ 1,098 $ 366 $ 1,406

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Schedule of Unconditional Purchase Obligations	The following is a schedule of unconditional purchase obligations required under the 25 MW Platte River Power Authority PPA as of September 30, 2019 (in thousands): 2019 $ 1,369 2020 $ 5,475 2021 $ 5,475 2022 $ 5,475 2023 $ 5,475 Thereafter $ 2,738

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	9 Months Ended
	Sep. 30, 2019
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	The following amounts by major classification are included in Accrued liabilities in the accompanying Condensed Consolidated Balance Sheets (in thousands) as of: September 30, 2019 December 31, 2018 Accrued employee compensation, benefits and withholdings $ 57,313 $ 63,742 Accrued property taxes 38,937 42,510 Customer deposits and prepayments 56,220 43,574 Accrued interest and contract adjustment payments 35,100 31,759 Other (none of which is individually significant) 30,262 33,916 Total accrued liabilities $ 217,832 $ 215,501

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Lessee Disclosure [Abstract]
Lease, Cost	The components of lease expense were as follows (in thousands): Income Statement Location Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Operating lease cost Operations and maintenance $ 380 $ 1,076 Finance lease cost: Amortization of right-of-use asset Depreciation, depletion and amortization 28 72 Interest on lease liabilities Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) 5 14 Total lease cost $ 413 $ 1,162
Lessee - Supplemental Balance Sheet Information	Supplemental balance sheet information related to leases was as follows (in thousands): Balance Sheet Location As of September 30, 2019 Assets: Operating lease assets Other assets, non-current $ 4,864 Finance lease assets Other assets, non-current 493 Total lease assets $ 5,357 Liabilities: Current: Operating leases Accrued liabilities $ 970 Finance lease Accrued liabilities 80 Noncurrent: Operating leases Other deferred credits and other liabilities 4,252 Finance lease Other deferred credits and other liabilities 419 Total lease liabilities $ 5,721
Lessee - Supplemental Cash Flow Information	Supplemental cash flow information related to leases was as follows (in thousands): Nine Months Ended September 30, 2019 Cash paid included in the measurement of lease liabilities: Operating cash flows from operating leases $ 895 Operating cash flows from finance lease $ 14 Financing cash flows from finance lease $ 66 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ 2,775 Finance lease $ 67
Lessee - Supplemental Weighted Average Schedule	As of September 30, 2019 Weighted average remaining lease term (years): Operating leases 8 years Finance lease 4 years Weighted average discount rate: Operating leases 4.27 % Finance lease 4.19 %
Lessee - Finance Lease, Liability, Maturity	As of September 30, 2019 , scheduled maturities of lease liabilities for future years were as follows (in thousands): Operating Leases Finance Lease Total 2019 (a) $ 368 $ 32 $ 400 2020 992 126 1,118 2021 855 126 981 2022 736 126 862 2023 714 126 840 Thereafter 2,682 10 2,692 Total lease payments (b) $ 6,347 $ 546 $ 6,893 Less imputed interest 1,125 47 1,172 Present value of lease liabilities $ 5,222 $ 499 $ 5,721 (a) Includes lease liabilities for the remaining three months of 2019 . (b) Lease payments exclude payments to landlords for common area maintenance, real estate taxes, and insurance.
Lessee, Operating Lease, Liability, Maturity	As of September 30, 2019 , scheduled maturities of lease liabilities for future years were as follows (in thousands): Operating Leases Finance Lease Total 2019 (a) $ 368 $ 32 $ 400 2020 992 126 1,118 2021 855 126 981 2022 736 126 862 2023 714 126 840 Thereafter 2,682 10 2,692 Total lease payments (b) $ 6,347 $ 546 $ 6,893 Less imputed interest 1,125 47 1,172 Present value of lease liabilities $ 5,222 $ 499 $ 5,721 (a) Includes lease liabilities for the remaining three months of 2019 . (b) Lease payments exclude payments to landlords for common area maintenance, real estate taxes, and insurance. As previously disclosed in Note 14 of the Notes to the Consolidated Financial Statements in our 2018 Annual Report on Form 10-K, prior to the adoption of ASU 2016-02, Leases (Topic 842), the future minimum payments required under operating lease agreements as of December 31, 2018 were as follows (in thousands): Operating Leases 2019 $ 1,052 2020 464 2021 344 2022 224 2023 216 Thereafter 1,776 Total lease payments $ 4,076
Lessor Disclosure [Abstract]
Operating Lease, Lease Income	The components of lease revenue were as follows (in thousands): Income Statement Location Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Operating lease income Revenue $ 544 $ 1,749
Lessor - Operating and Finance Lease, Liability, Maturity	As of September 30, 2019 , scheduled maturities of lease receivables for future years were as follows (in thousands): Operating Leases 2019 (a) $ 551 2020 2,035 2021 1,857 2022 1,793 2023 1,799 Thereafter 55,481 Total lease receivables $ 63,516 (a) Includes lease receivables for the remaining three months of 2019 .

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2019
Investments, All Other Investments [Abstract]
Investments	The following table presents the carrying value of our investments (in thousands) as of: September 30, 2019 December 31, 2018 Investment in privately held oil and gas company $ 8,359 $ 28,100 Cash surrender value of life insurance contracts 12,907 12,812 Other investments 317 101 Total investments $ 21,583 $ 41,013

Management's Statement (Details

Management's Statement (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease - right of use assets	$ 4,864
Operating lease obligation liability	5,222
Cumulative effect of the adoption, net of tax impact	$ 3	$ (3)	$ 3,390
Leases, ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease - right of use assets				$ 3,100
Operating lease obligation liability				3,200
Accrued rent receivable				4,500
Cumulative effect of the adoption, net of tax impact				$ 3,400

Disaggregation of Revenue (Deta

Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 323,745	$ 320,163	$ 1,251,461	$ 1,245,981
Total revenues	325,548	321,979	1,257,246	1,253,072
Recasting of Intercompany Capital Lease
Disaggregation of Revenue [Line Items]
Changes To Our Segment Performance Measure - Revenues		0		0
Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,846	8,809	19,934	25,892
Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	316,899	311,354	1,231,527	1,220,089
Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	1,803	1,816	5,785	7,091
Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	258,870	254,418	1,043,058	1,041,190
Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	28,824	29,812	101,256	99,783
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9,915	9,693	29,061	29,784
Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5,103	7,850	12,062	13,339
Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21,033	18,390	66,024	61,885
Inter-company Revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(28,449)	(27,185)	(82,796)	(80,693)
Total revenues	(37,943)	(36,279)	(111,502)	(108,030)
Inter-company Revenues | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(8,146)	(7,942)	(23,315)	(23,761)
Inter-company Revenues | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(20,303)	(19,243)	(59,481)	(56,932)
Inter-company Revenues | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(9,494)	(9,094)	(28,706)	(27,337)
Inter-company Revenues | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(8,146)	(7,941)	(23,315)	(23,761)
Inter-company Revenues | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(195)	(267)	(903)	(977)
Inter-company Revenues | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(14,414)	(13,935)	(40,923)	(39,457)
Inter-company Revenues | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1,488)	(1,349)	(5,047)	(5,531)
Inter-company Revenues | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(4,206)	(3,693)	(12,608)	(10,967)
Electric Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	191,150	184,559	538,200	529,743
Total revenues	191,384	184,790	540,665	531,961
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	191,150	184,559	538,200	529,743
Electric Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	234	231	2,465	2,218
Electric Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	162,214	157,049	455,409	449,482
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	8,210	8,255	23,334	25,497
Electric Utilities | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,452	9,059	16,592	18,142
Electric Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,274	10,196	42,865	36,622
Gas Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	129,933	130,665	706,158	703,534
Total revenues	130,744	131,676	707,293	706,640
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	129,933	130,665	706,158	703,534
Gas Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	811	1,011	1,135	3,106
Gas Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	89,810	88,559	567,715	565,816
Gas Utilities | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	29,019	30,079	102,159	100,760
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	139	140	517	728
Gas Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10,965	11,887	35,767	36,230
Power Generation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16,119	15,373	46,650	43,744
Total revenues	25,811	24,491	75,764	71,173
Power Generation | Recasting of Intercompany Capital Lease
Disaggregation of Revenue [Line Items]
Changes To Our Segment Performance Measure - Revenues		900		2,600
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	16,119	15,373	46,650	43,744
Power Generation | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	9,692	9,118	29,114	27,429
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	16,119	15,373	46,650	43,744
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	14,992	16,751	43,249	49,653
Total revenues	15,552	17,301	45,026	51,328
Mining | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,992	16,751	43,249	49,653
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	560	550	1,777	1,675
Mining | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,992	16,751	43,249	49,653
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: Intercompany PPA (Details)	Sep. 30, 2019MW
Energy and Capacity to Colorado Electric from Colorado IPP
Segment Reporting Information
Utility Plant, Megawatt Capacity	200

Business Segment Information__2

Business Segment Information: Information Relating to Segment Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information
Revenue from contracts with customers	$ 323,745	$ 320,163	$ 1,251,461	$ 1,245,981
Revenues	325,548	321,979	1,257,246	1,253,072
Operating income	70,551	65,085	284,683	282,910
Interest expense, net	(33,487)	(35,297)	(102,469)	(104,826)
Impairment of investment	(19,741)	0	(19,741)	0
Other Nonoperating Income (Expense) Including Allowance For Funds Used During Construction, Equity	580	(510)	55	(1,923)
Income tax benefit (expense)	(2,508)	(7,477)	(22,078)	11,784
Income from continuing operations	15,395	21,801	140,450	187,945
Net (loss) from discontinued operations	0	(857)	0	(5,627)
Net income	15,395	20,944	140,450	182,318
Net income attributable to noncontrolling interest	(3,655)	(3,994)	(10,319)	(10,447)
Net income available for common stock	11,740	16,950	130,131	171,871
Changes To Our Segment Performance Measure - Operating Income		0		0
Deferred income taxes			24,381	(14,396)
Legal Entity Restructuring
Segment Reporting Information
Deferred income taxes				49,000
Recasting of Intercompany Capital Lease
Segment Reporting Information
Changes To Our Segment Performance Measure - Revenues		0		0
Inter-company Revenues
Segment Reporting Information
Revenue from contracts with customers	(28,449)	(27,185)	(82,796)	(80,693)
Revenues	(37,943)	(36,279)	(111,502)	(108,030)
Consolidation, Eliminations
Segment Reporting Information
Revenue from contracts with customers	0	0	0	0
Corporate
Segment Reporting Information
Operating income	(34)	(178)	(439)	(2,709)
Changes To Our Segment Performance Measure - Operating Income		(200)		(400)
Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	191,150	184,559	538,200	529,743
Revenues	191,384	184,790	540,665	531,961
Operating income	50,653	43,393	125,219	123,073
Changes To Our Segment Performance Measure - Operating Income		1,600		4,800
Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	129,933	130,665	706,158	703,534
Revenues	130,744	131,676	707,293	706,640
Operating income	4,736	4,240	116,607	116,168
Power Generation
Segment Reporting Information
Revenue from contracts with customers	16,119	15,373	46,650	43,744
Revenues	25,811	24,491	75,764	71,173
Operating income	11,822	13,079	33,945	33,731
Changes To Our Segment Performance Measure - Operating Income		(1,400)		(4,400)
Power Generation | Recasting of Intercompany Capital Lease
Segment Reporting Information
Changes To Our Segment Performance Measure - Revenues		900		2,600
Mining
Segment Reporting Information
Revenue from contracts with customers	14,992	16,751	43,249	49,653
Revenues	15,552	17,301	45,026	51,328
Operating income	3,374	4,551	9,351	12,647
Other Revenues
Segment Reporting Information
Revenues	1,803	1,816	5,785	7,091
Other Revenues | Inter-company Revenues
Segment Reporting Information
Revenues	(9,494)	(9,094)	(28,706)	(27,337)
Other Revenues | Consolidation, Eliminations
Segment Reporting Information
Revenues	0	0	0	0
Other Revenues | Electric Utilities
Segment Reporting Information
Revenues	234	231	2,465	2,218
Other Revenues | Gas Utilities
Segment Reporting Information
Revenues	811	1,011	1,135	3,106
Other Revenues | Power Generation
Segment Reporting Information
Revenues	9,692	9,118	29,114	27,429
Other Revenues | Mining
Segment Reporting Information
Revenues	560	550	1,777	1,675
External Operating Revenue
Segment Reporting Information
Revenue from contracts with customers	323,745	320,163	1,251,461	1,245,981
External Operating Revenue | Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	185,811	179,527	521,614	513,270
External Operating Revenue | Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	129,385	130,390	704,188	702,532
External Operating Revenue | Power Generation
Segment Reporting Information
Revenue from contracts with customers	1,703	1,437	5,725	4,287
External Operating Revenue | Mining
Segment Reporting Information
Revenue from contracts with customers	6,846	8,809	19,934	25,892
External Operating Revenue | Other Revenues
Segment Reporting Information
Revenues	1,803	1,816	5,785	7,091
External Operating Revenue | Other Revenues | Electric Utilities
Segment Reporting Information
Revenues	234	231	2,465	2,218
External Operating Revenue | Other Revenues | Gas Utilities
Segment Reporting Information
Revenues	810	1,011	1,134	3,106
External Operating Revenue | Other Revenues | Power Generation
Segment Reporting Information
Revenues	531	348	1,401	1,066
External Operating Revenue | Other Revenues | Mining
Segment Reporting Information
Revenues	228	226	785	701
Inter-company Operating Revenue | Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	5,339	5,032	16,586	16,473
Inter-company Operating Revenue | Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	549	275	1,971	1,002
Inter-company Operating Revenue | Power Generation
Segment Reporting Information
Revenue from contracts with customers	14,415	13,936	40,924	39,457
Inter-company Operating Revenue | Mining
Segment Reporting Information
Revenue from contracts with customers	8,146	7,942	23,315	23,761
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	9,162	8,770	27,714	26,363
Inter-company Operating Revenue | Other Revenues | Mining
Segment Reporting Information
Revenues	$ 332	$ 324	$ 992	$ 974

Business Segment Information_ S

Business Segment Information: Segment and Corporate Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 7,274,950	$ 6,963,327
Corporate
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	174,302	209,478
Electric Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,810,108	2,707,695
Gas Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	3,797,941	3,623,475
Power Generation
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	414,526	342,085
Mining
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 78,073	80,594
Recasting of Intercompany Capital Lease
Segment Reporting, Asset Reconciling Item [Line Items]
Changes To Our Segment Performance Measure - Assets		0
Recasting of Intercompany Capital Lease | Electric Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Changes To Our Segment Performance Measure - Assets		(188,000)
Recasting of Intercompany Capital Lease | Power Generation
Segment Reporting, Asset Reconciling Item [Line Items]
Changes To Our Segment Performance Measure - Assets		$ 188,000

Accounts Receivable (Details)

Accounts Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts Receivable [Line Items]
Accounts Receivable, Trade	$ 96,214	$ 146,716
Unbilled Receivables, Current	55,934	125,646
Allowance for Doubtful Accounts	(3,159)	(3,209)
Accounts receivable, net	148,989	269,153
Corporate
Accounts Receivable [Line Items]
Accounts Receivable, Trade	6,261	5,008
Unbilled Receivables, Current	0	0
Allowance for Doubtful Accounts	(169)	(169)
Accounts receivable, net	6,092	4,839
Electric Utilities
Accounts Receivable [Line Items]
Accounts Receivable, Trade	39,151	39,721
Unbilled Receivables, Current	31,843	35,125
Allowance for Doubtful Accounts	(500)	(448)
Accounts receivable, net	70,494	74,398
Gas Utilities
Accounts Receivable [Line Items]
Accounts Receivable, Trade	46,265	96,123
Unbilled Receivables, Current	24,091	90,521
Allowance for Doubtful Accounts	(2,490)	(2,592)
Accounts receivable, net	67,866	184,052
Power Generation
Accounts Receivable [Line Items]
Accounts Receivable, Trade	2,733	1,876
Unbilled Receivables, Current	0	0
Allowance for Doubtful Accounts	0	0
Accounts receivable, net	2,733	1,876
Mining
Accounts Receivable [Line Items]
Accounts Receivable, Trade	1,804	3,988
Unbilled Receivables, Current	0	0
Allowance for Doubtful Accounts	0	0
Accounts receivable, net	$ 1,804	$ 3,988

Regulatory Accounting (Details)

Regulatory Accounting (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Regulatory assets
Regulatory assets	$ 260,358	$ 284,235
Less current regulatory assets	(46,206)	(48,776)
Regulatory assets, non-current	214,152	235,459
Regulatory liabilities
Regulatory liabilities	523,941	540,794
Less current regulatory liabilities	(25,168)	(29,810)
Regulatory liabilities, non-current	498,773	510,984
Deferred energy and gas costs
Regulatory liabilities
Regulatory liabilities	9,919	6,991
Employee benefit plans
Regulatory liabilities
Regulatory liabilities	42,737	42,533
Cost of removal
Regulatory liabilities
Regulatory liabilities	162,169	150,123
Excess deferred income taxes
Regulatory liabilities
Regulatory liabilities	286,587	310,562
TCJA revenue reduction
Regulatory liabilities
Regulatory liabilities	2,770	18,032
Other regulatory liabilities
Regulatory liabilities
Regulatory liabilities	19,759	12,553
Deferred energy and gas costs
Regulatory assets
Regulatory assets	31,832	29,661
Deferred gas cost adjustments
Regulatory assets
Regulatory assets	3,899	3,362
Gas price derivatives
Regulatory assets
Regulatory assets	4,296	6,201
Deferred taxes on AFUDC
Regulatory assets
Regulatory assets	7,691	7,841
Employee benefit plans
Regulatory assets
Regulatory assets	107,921	110,524
Environmental
Regulatory assets
Regulatory assets	917	959
Loss on reacquired debt
Regulatory assets
Regulatory assets	19,710	21,001
Renewable energy standard adjustment
Regulatory assets
Regulatory assets	2,871	1,722
Deferred taxes on flow through accounting
Regulatory assets
Regulatory assets	37,609	31,044
Decommissioning costs
Regulatory assets
Regulatory assets	11,206	11,700
Gas supply contract termination
Regulatory assets
Regulatory assets	9,953	14,310
Other regulatory assets
Regulatory assets
Regulatory assets	$ 22,453	$ 45,910

Regulatory Accounting_ Rate Rev

Regulatory Accounting: Rate Review (Details) $ in Millions	Jun. 25, 2019USD ($)	Jun. 03, 2019USD ($)utility	Feb. 01, 2019USD ($)utility	Nov. 01, 2019MW	Oct. 29, 2019utility	Sep. 30, 2019USD ($)utilityMW
Wyoming Public Service Commission (WPSC) | Black Hills Energy, Wyoming Gas | Rate Review Filed with the Regulatory Agency
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase, Amount | $		$ 16
Public Utilities, Number of Companies Being Merged		4
Wyoming Public Service Commission (WPSC) and South Dakota Public Utilities Commission (SDPUC) | South Dakota Electric and Wyoming Electric | Corriedale Wind Project
Public Utilities, General Disclosures [Line Items]
Public Utilities, Property, Plant and Equipment, Cost Of Plant Investment | $						$ 57
Utility Plant, Megawatt Capacity | MW						40
Public Utilities, Number of Electric Utilities Jointly Owning Wind Project						2
Wyoming Public Service Commission (WPSC) and South Dakota Public Utilities Commission (SDPUC) | South Dakota Electric and Wyoming Electric | Corriedale Wind Project | Customer Subscription Period Was Completed With Customer Interest Fulfilling All Available Energy
Public Utilities, General Disclosures [Line Items]
Utility Plant, Megawatt Capacity | MW						40
Kansas Corporation Commission | Black Hills Energy, Kansas Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount | $	$ 1.4
Colorado Public Utilities Commission (CPUC) | Black Hills Energy, Colorado Gas | Rate Review Filed with the Regulatory Agency
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase, Amount | $			$ 2.5
Public Utilities, Number of Companies Being Merged			2
Subsequent Event | South Dakota Public Utilities Commission (SDPUC) | South Dakota Electric | Corriedale Wind Project | Amount of Increase sought in Generating Capacity Under Environmental Improvement Adjustment Tariff
Public Utilities, General Disclosures [Line Items]
Utility Plant, Megawatt Capacity | MW				12.5
Subsequent Event | South Dakota Public Utilities Commission (SDPUC) | South Dakota Electric | Corriedale Wind Project | New Total Sought In Generating Capacity Under Environmental Improvement Adjustment Tariff
Public Utilities, General Disclosures [Line Items]
Utility Plant, Megawatt Capacity | MW				32.5
Subsequent Event | Nebraska Public Service Commission (NPSC) | Black Hills Energy, Nebraska Gas | Application Filed
Public Utilities, General Disclosures [Line Items]
Public Utilities, Number of Companies Being Merged					2
Subsequent Event | Nebraska Public Service Commission (NPSC) | Black Hills Energy, Nebraska Gas | Rate Review Expected To Be Filed In The Next Fiscal Year
Public Utilities, General Disclosures [Line Items]
Public Utilities, Number of Companies Being Merged					2

Materials, Supplies and Fuel (D

Materials, Supplies and Fuel (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Inventory, Net [Abstract]
Materials and supplies	$ 81,382	$ 75,081
Fuel - Electric Utilities	2,535	2,850
Natural gas in storage held for distribution	39,085	39,368
Total materials, supplies and fuel	$ 123,002	$ 117,299

Earnings Per Share_ Earnings Pe

Earnings Per Share: Earnings Per Share Reconciliation (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income available for common stock	$ 11,740	$ 16,950	$ 130,131	$ 171,871
Weighted average shares - basic (in shares)	60,976	53,364	60,458	53,346
Dilutive effect of:
Equity Units (in shares)	0	1,344	0	1,060
Equity compensation (in shares)	128	111	120	102
Weighted average shares - diluted (in shares)	61,104	54,819	60,578	54,508

Earnings Per Share_ Anti-diluti

Earnings Per Share: Anti-dilutive shares (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	2	12	5	15
Equity compensation - (in shares)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	2	12	4	15
Restricted Stock (in shares)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	0	0	1	0

Notes Payable, Current Maturi_3

Notes Payable, Current Maturities and Debt: Schedule of Short-term Debt and Narrative (Details)	9 Months Ended
	Sep. 30, 2019USD ($)credit_extension	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Short-term Debt [Line Items]
Notes payable	$ 294,900,000		$ 185,620,000
Letters of Credit	18,313,000		22,311,000
Commercial paper, maximum borrowing capacity	750,000,000
Net (payments) borrowings of short-term debt	109,280,000	$ (99,200,000)
Commercial Paper
Short-term Debt [Line Items]
Notes payable	$ 244,900,000		185,620,000
Debt instrument, term	397 days
Net (payments) borrowings of short-term debt	$ 109,000,000
Short-term interest rate	2.43%
Revolving Credit Facility
Short-term Debt [Line Items]
Notes payable	$ 50,000,000		0
Letters of Credit	18,313,000		$ 22,311,000
Current borrowing capacity	$ 750,000,000
Number of one-year extension options | credit_extension	2
Debt instrument, term	1 year
Maximum borrowing capacity	$ 1,000,000,000
Commitment fee	0.175%
Revolving Credit Facility | Base Rate
Short-term Debt [Line Items]
Interest rate	0.125%
Revolving Credit Facility | Eurodollar
Short-term Debt [Line Items]
Interest rate	1.125%
Revolving Credit Facility | Letter of Credit
Short-term Debt [Line Items]
Interest rate	1.125%

Notes Payable, Current Maturi_4

Notes Payable, Current Maturities and Debt: Debt Covenants (Details)	Sep. 30, 2019
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: Long-Term Debt (Details) - Black Hills Corporation - Corporate $ in Millions	Jun. 17, 2019USD ($)
Corporate Term Loan Due June 2021
Proceeds from Issuance of Debt	$ 400
Corporate Term Loan Due July 2020
Extinguishment of Debt, Amount	$ 300

Notes Payable, Current Maturi_6

Notes Payable, Current Maturities and Debt: Subsequent Event - Debt Offering (Details) - Subsequent Event $ in Millions	Oct. 03, 2019USD ($)
Corporate
Subsequent Event [Line Items]
Proceeds from Issuance of Debt	$ 700
Senior Unsecured Notes Due 2029 | Corporate
Subsequent Event [Line Items]
Proceeds from Issuance of Debt	$ 400
Debt Instrument, Interest Rate, Stated Percentage	3.05%
Senior Unsecured Notes Due 2049 | Corporate
Subsequent Event [Line Items]
Proceeds from Issuance of Debt	$ 300
Debt Instrument, Interest Rate, Stated Percentage	3.875%
Corporate Term Loan Due June 2021
Subsequent Event [Line Items]
Extinguishment of Debt, Amount	$ 400
Senior Unsecured Notes Due 2020
Subsequent Event [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.875%
Extinguishment of Debt, Amount	$ 200

Equity_ At-the-Market Equity Of

Equity: At-the-Market Equity Offering Program (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Aug. 04, 2017
At The Market Equity Offering Program Authorized Aggregate Value			$ 300
Payments of Stock Issuance Costs	$ 0.3	$ 1
Common Stock
At The Market Equity Program Proceeds from Sale of Stock	$ 30	$ 99
At The Market Equity Offering Program Shares Issued	389,237	1,328,332

Risk Management Activities_ Uti

Risk Management Activities: Utilities (Details) - Natural Gas, Distribution $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019USD ($)MMBTU	Dec. 31, 2018MMBTU
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months | $	$ 0.4
Cash Flow Hedging
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	1,812,500
Natural gas futures purchased
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	2,350,000	4,000,000
Derivative, Remaining Maturity	15 months	24 months
Natural gas options purchased, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	8,580,000	4,320,000
Derivative, Remaining Maturity	6 months	13 months
Natural gas basis swaps purchased
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	2,090,000	3,960,000
Derivative, Remaining Maturity	15 months	24 months
Natural gas over-the-counter swaps, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	5,460,000	3,660,000
Derivative, Remaining Maturity	25 months	24 months
Credit Risk Derivative Liabilities, at Fair Value | $	$ 0.5
Natural gas physical contracts, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	23,459,639	18,325,852
Derivative, Remaining Maturity	6 months	30 months

Risk Management Activities_ Cas

Risk Management Activities: Cash Flow Hedges (Details) - Cash Flow Hedging - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (842)	$ (730)	$ (1,631)	$ (2,940)
Designated as Hedging Instrument
Derivative [Line Items]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax	692	760	1,197	2,721
Interest rate swaps | Designated as Hedging Instrument
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	713	712	2,139	2,138
Commodity Contract | Designated as Hedging Instrument
Derivative [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	(150)	30	(434)	(219)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	129	18	(508)	802
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)	(712)	(2,139)	(2,138)
Cost of Sales | Commodity Contract
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (129)	$ (18)	$ 508	$ (802)

Risk Management Activities_ Der

Risk Management Activities: Derivatives Not Designated as Hedge Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Derivative [Line Items]
Regulatory assets	$ 260,358		$ 260,358		$ 284,235
Gas price derivatives
Derivative [Line Items]
Regulatory assets	4,296		4,296		$ 6,201
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	122	$ (96)	(1,038)	$ 929
Not Designated as Hedging Instrument | Cost of Sales
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(20)	(96)	(1,180)	929
Not Designated as Hedging Instrument | Other Nonoperating Income (Expense)
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 142	$ 0	$ 142	$ 0

Fair Value Measurements_ Schedu

Fair Value Measurements: Schedule of Fair Values (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
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	$ (2,335)	$ (1,408)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(3,471)	(5,794)
Utilities Group
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	(2,335)	(1,408)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(3,471)	(5,794)
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	415	1,519
Derivative Liabilities, Total	2,609	1,007
Estimate of Fair Value Measurement | Utilities Group
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	415	1,519
Derivative Liabilities, Fair Value Disclosure	2,609	1,007
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 1 | Utilities Group
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	0	0
Derivative Liabilities, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	2,750	2,927
Derivative Liabilities, Total	6,080	6,801
Fair Value, Inputs, Level 2 | Utilities Group
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	2,750	2,927
Derivative Liabilities, Fair Value Disclosure	6,080	6,801
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	0	0
Derivative Liabilities, Total	0	0
Fair Value, Inputs, Level 3 | Utilities Group
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	0	0
Derivative Liabilities, Fair Value Disclosure	$ 0	$ 0

Fair Value Measurements_ Balanc

Fair Value Measurements: Balance Sheet Location (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Designated as Hedging Instrument
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Asset, Fair Value, Net	$ (495)	$ 315
Not Designated as Hedging Instrument
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Asset, Fair Value, Net	(1,699)	197
Commodity Contract | Designated as Hedging Instrument | Derivative assets — current
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	415
Commodity Contract | Designated as Hedging Instrument | Other assets, non-current
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	2	18
Commodity Contract | Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(427)	(114)
Commodity Contract | Designated as Hedging Instrument | Other deferred credits and other liabilities
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(70)	(4)
Commodity Contract | Not Designated as Hedging Instrument | Derivative assets — current
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	412	1,085
Commodity Contract | Not Designated as Hedging Instrument | Other assets, non-current
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1	1
Commodity Contract | Not Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(1,969)	(833)
Commodity Contract | Not Designated as Hedging Instrument | Other deferred credits and other liabilities
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ (143)	$ (56)

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, including current maturities	$ 3,054,978	$ 2,956,578
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, including current maturities, Fair Value	$ 3,424,747	$ 3,039,108

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss): Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	$ 17,903	$ 29,278	$ 162,528	$ 176,161
Income tax benefit (expense)	(2,508)	(7,477)	(22,078)	11,784
Net income	15,395	20,944	140,450	182,318
Operations and maintenance	117,037	115,699	366,907	352,092
Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net income	(647)	(1,030)	(1,555)	(3,649)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges | Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(842)	(730)	(1,631)	(2,940)
Income tax benefit (expense)	170	149	358	643
Net income	(672)	(581)	(1,273)	(2,297)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) | Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operations and maintenance	20	44	59	133
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) | Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Operations and maintenance	(84)	(621)	(525)	(1,865)
Accumulated Defined Benefit Plans Adjustment | Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(64)	(577)	(466)	(1,732)
Income tax benefit (expense)	89	128	184	380
Net income	25	(449)	(282)	(1,352)
Cash Flow Hedging
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(842)	(730)	(1,631)	(2,940)
Interest Expense | Cash Flow Hedging | Interest rate swaps
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(713)	(712)	(2,139)	(2,138)
Cost of Sales | Cash Flow Hedging | Commodity Contract
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (129)	$ (18)	$ 508	$ (802)

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss): Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	$ (26,916)	$ (41,202)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(25,695)	(37,703)
Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	(9,937)	(21,103)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Reclassification from AOCI, Current Period, Tax		3
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(9,655)	(19,748)
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	282	1,352
Accumulated Other Comprehensive Income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(334)	(168)
Reclassification from AOCI, Current Period, Tax		18
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	1,555	3,649
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	(17,307)	(19,581)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Reclassification from AOCI, Current Period, Tax		15
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(15,668)	(17,884)
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	1,639	1,682
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	328	(518)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(334)	(168)
Reclassification from AOCI, Current Period, Tax		0
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(372)	(71)
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	$ (366)	$ 615

Supplemental Disclosure of Ca_3

Supplemental Disclosure of Cash Flow Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Non-cash Investing and Financing Activities from Continuing Operations [Abstract]
Property, plant and equipment acquired with accrued liabilities	$ 86,661	$ 49,631
Supplemental Cash Flow Elements [Abstract]
Interest (net of amounts capitalized)	(99,375)	(104,035)
Income taxes	$ 2,255	$ (14,842)

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 1,346	$ 1,708	$ 4,037	$ 5,125
Interest cost	4,344	3,867	13,031	11,602
Expected return on plan assets	(6,100)	(6,185)	(18,300)	(18,555)
Prior service cost (benefit)	6	15	19	44
Net loss (gain)	941	2,158	2,822	6,473
Net periodic benefit cost	537	1,563	1,609	4,689
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	12,700		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	454	573	1,362	1,718
Interest cost	560	521	1,683	1,563
Expected return on plan assets	(57)	(57)	(172)	(170)
Prior service cost (benefit)	(99)	(99)	(298)	(297)
Net loss (gain)	0	54	0	162
Net periodic benefit cost	858	992	2,575	2,976
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	1,109		3,326
Estimated Future Employer Contributions in Current Fiscal Year	1,109		1,109
Estimated Future Employer Contributions in Next Fiscal Year	4,815		4,815
Supplemental Non-qualified Defined Benefit and Defined Contribution Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	429	632	2,406	1,347
Interest cost	324	293	972	878
Prior service cost (benefit)	0	0	1	1
Net loss (gain)	134	250	402	750
Net periodic benefit cost	887	$ 1,175	3,781	$ 2,976
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	366		1,098
Estimated Future Employer Contributions in Current Fiscal Year	366		366
Estimated Future Employer Contributions in Next Fiscal Year	$ 1,406		$ 1,406

Commitments and Contingencies_

Commitments and Contingencies: Future Purchase Agreement - Related Party (Details) - Black Hills Wyoming and Wyoming Electric - Federal Energy Regulatory Commission (FERC)	Aug. 02, 2019MW
Unrecorded Unconditional Purchase Obligation [Line Items]
Pending FERC Approval - Number of Megawatts Capacity to be Purchased and Delivered Through Intercompany Agreement	60
Unrecorded Unconditional Purchase Obligation, Term	20 years

Commitments and Contingencies_2

Commitments and Contingencies: Platte River Power Authority PPA's (Details) $ in Thousands	Sep. 30, 2019USD ($)MW
Platte River Power Authority Wind Power Agreement
Unrecorded Unconditional Purchase Obligation [Line Items]
Utility Plant, Megawatt Capacity | MW	60
Platte River Power Authority
Unrecorded Unconditional Purchase Obligation [Line Items]
Utility Plant, Megawatt Capacity | MW	25
Platte River Power Authority | Power Purchase Agreements
Unrecorded Unconditional Purchase Obligation [Line Items]
2019	$ 1,369
2020	5,475
2021	5,475
2022	5,475
2023	5,475
Thereafter	$ 2,738

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income tax benefit (expense)	$ (2,508)	$ (7,477)	$ (22,078)	$ 11,784
Income tax (expense) benefit associated with changes in the prior estimated impact of tax reform on deferred income taxes		$ (5,300)	1,000	(7,500)
Deferred Income Tax (Expense) Benefit			$ 24,381	$ (14,396)
Effective Tax Rate	14.00%	7.60%	13.60%	17.10%
Production tax credits			$ 5,000
Legal Entity Restructuring
Deferred Income Tax (Expense) Benefit				$ 49,000

Accrued Liabilities (Details)

Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued employee compensation, benefits and withholdings	$ 57,313	$ 63,742
Accrued property taxes	38,937	42,510
Customer deposits and prepayments	56,220	43,574
Accrued interest and contract adjustment payments	35,100	31,759
Other (none of which is individually significant)	30,262	33,916
Total accrued liabilities	$ 217,832	$ 215,501

Lessee (Details)

Lessee (Details)	9 Months Ended
	Sep. 30, 2019
Minimum
Lessee, Lease, Description [Line Items]
Lessee - Lease Term	1 year
Maximum
Lessee, Lease, Description [Line Items]
Lessee - Lease Term	37 years

Lessee - Lease Costs (Details)

Lessee - Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Leases [Abstract]
Operating lease cost	$ 380	$ 1,076
Amortization of right-of-use asset	28	72
Interest on lease liabilities	5	14
Total lease cost	$ 413	$ 1,162

Lessee - Supplemental Balance S

Lessee - Supplemental Balance Sheet Information (Details) $ in Thousands	Sep. 30, 2019USD ($)
Leases [Abstract]
Operating lease assets	$ 4,864
Finance lease assets	493
Total lease assets	5,357
Operating lease liability, current	970
Finance lease liability, current	80
Operating lease liability, non-current	4,252
Finance lease liability, non-current	419
Total lease liabilities	$ 5,721

Lessee - Supplemental Cash Flow

Lessee - Supplemental Cash Flow Information (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019USD ($)
Leases [Abstract]
Operating cash flows from operating leases	$ 895
Operating cash flows from finance lease	14
Financing cash flows from finance lease	66
Operating leases	2,775
Finance lease	$ 67

Lessee - Weighted Average Infor

Lessee - Weighted Average Information (Details)	Sep. 30, 2019
Leases [Abstract]
Operating leases	8 years
Finance lease	4 years
Operating leases	4.27%
Finance lease	4.19%

Lessee - Future Minimum Payment

Lessee - Future Minimum Payments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Operating Leases
2019	$ 368
2020	992
2021	855
2022	736
2023	714
Thereafter	2,682
Total lease payments	6,347
Less imputed interest	1,125
Present Value of Lease Liabilities - Operating leases	5,222
Finance Lease
2019	32
2020	126
2021	126
2022	126
2023	126
Thereafter	10
Total lease payments	546
Less imputed interest	47
Present value of lease liabilities - Finance Leases	499
Operating and Finance Lease Total
2019	400
2020	1,118
2021	981
2022	862
2023	840
Thereafter	2,692
Total lease payments	6,893
Less imputed interest	1,172
Present value of lease liabilities	$ 5,721
Prior Year End Operating Lease Future Minimum Payments
2019		$ 1,052
2020		464
2021		344
2022		224
2023		216
Thereafter		1,776
Total lease payments		$ 4,076

Lessor (Details)

Lessor (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)
Lessor, Lease, Description [Line Items]
Operating lease income	$ 544	$ 1,749
Minimum
Lessor, Lease, Description [Line Items]
Lessor - Lease Term	1 year	1 year
Maximum
Lessor, Lease, Description [Line Items]
Lessor - Lease Term	35 years	35 years

Lessor - Future Minimum Payment

Lessor - Future Minimum Payments (Details) $ in Thousands	Sep. 30, 2019USD ($)
Operating Leases
2019	$ 551
2020	2,035
2021	1,857
2022	1,793
2023	1,799
Thereafter	55,481
Total lease receivables	$ 63,516

Investments (Details)

Investments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Feb. 28, 2018
Assets Held For Sale Used to Acquire Other Investments						$ 28,000
Impairment of investment	$ 19,741	$ 0	$ 19,741	$ 0
Investments	21,583		21,583		$ 41,013
Investment in privately held oil and gas company
Investments	8,359		8,359		28,100
Cash surrender value of life insurance contracts
Investments	12,907		12,907		12,812
Total investments
Investments	$ 317		$ 317		$ 101
Valuation, Income Approach
Discount Rate Used in Valuation of Fair Value of Oil and Gas Reserve Quantities	10.00%		10.00%