Black Hills (BKH) 10-Q 3 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information Document - shares	3 Months Ended
	Mar. 31, 2019	Apr. 30, 2019
Document and Entity Information [Abstract]
Trading Symbol	BKH
Entity Registrant Name	BLACK HILLS CORP /SD/
Entity Central Index Key	0001130464
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		60,367,972
Entity Emerging Growth Company	false
Entity Small Business	false

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Total revenues	$ 597,810	$ 575,389
Operating expenses:
Fuel, purchased power and cost of natural gas sold	248,779	247,639
Operations and maintenance	123,913	116,096
Depreciation, depletion and amortization	51,028	48,590
Taxes - property and production	13,519	13,300
Other operating expenses	440	1,490
Total operating expenses	437,679	427,115
Operating income	160,131	148,274
Interest charges -
Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts)	(35,974)	(35,438)
Allowance for funds used during construction - borrowed	958	133
Interest income	299	310
Allowance for funds used during construction - equity	48	68
Other income (expense), net	(837)	(172)
Total other income (expense)	(35,506)	(35,099)
Income before income taxes	124,625	113,175
Income tax benefit (expense)	(17,263)	25,802
Income from continuing operations	107,362	138,977
Net (loss) from discontinued operations	0	(2,343)
Net income	107,362	136,634
Net income attributable to noncontrolling interest	(3,554)	(3,630)
Net income from continuing operations	103,808	135,347
Net income available for common stock	$ 103,808	$ 133,004
Earnings Per Share, Basic [Abstract]
Income from continuing operations, Basic (usd per share)	$ 1.73	$ 2.54
(Loss) from discontinued operations, Basic (usd per share)	0	(0.05)
Earnings (loss) per share, Basic (usd per share)	1.73	2.49
Earnings Per Share, Diluted [Abstract]
Income from continuing operations, Diluted (usd per share)	1.73	2.50
(Loss) from discontinued operations, Diluted (usd per share)	0	(0.04)
Earnings (loss) per share, Diluted (usd per share)	$ 1.73	$ 2.46
Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract]
Basic (in shares)	59,920	53,319
Diluted (in shares)	60,060	54,122

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net income	$ 107,362	$ 136,634
Other comprehensive income (loss), net of tax:
Reclassification adjustments of benefit plan liability - prior service cost	(14)	(35)
Reclassification adjustments of benefit plan liability - net gain (loss)	167	486
Other comprehensive income, net of tax	457	1,260
Comprehensive income	107,819	137,894
Less: comprehensive income attributable to noncontrolling interest	(3,554)	(3,630)
Comprehensive income available for common stock	104,265	134,264
Interest rate swaps
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses	550	561
Commodity Contract
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses	(426)	476
Net unrealized gains (losses)	$ 180	$ (228)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification adjustment of benefit plan - prior service cost, (tax) benefit	$ 5	$ 10
Reclassification adjustment of benefit plan liabilities, (tax) benefit	(53)	(136)
Interest rate swaps
Reclassification of net realized gains/losses, (tax) benefit	(163)	(152)
Commodity Contract
Net unrealized gains/losses, (tax) benefit	(54)	69
Reclassification of net realized gains/losses, (tax) benefit	$ 128	$ (145)

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Current assets:
Cash and cash equivalents	$ 12,225	$ 20,776	$ 30,947
Restricted cash	3,494	3,369	2,958
Accounts receivable, net	282,602	269,153	257,772
Materials, supplies and fuel	87,676	117,299	82,045
Derivative assets, current	932	1,500	295
Income tax receivable, net	15,309	12,978	13,900
Regulatory assets, current	54,303	48,776	54,492
Other current assets	28,029	29,982	24,972
Current assets held for sale	0	0	24,724
Total current assets	484,570	503,833	492,105
Investments	41,247	41,013	40,927
Property, plant and equipment	6,127,050	6,000,015	5,608,539
Less: accumulated depreciation and depletion	(1,187,112)	(1,145,136)	(1,048,933)
Total property, plant and equipment, net	4,939,938	4,854,879	4,559,606
Other assets:
Goodwill	1,299,454	1,299,454	1,299,454
Intangible assets, net	14,136	14,337	7,357
Regulatory assets, non-current	232,404	235,459	212,740
Other assets, non-current	25,823	14,352	14,800
Total other assets, non-current	1,571,817	1,563,602	1,534,351
TOTAL ASSETS	7,037,572	6,963,327	6,626,989
Current liabilities:
Accounts payable	178,678	210,609	106,281
Accrued liabilities	196,072	215,501	194,040
Derivative liabilities, current	95	947	891
Regulatory liabilities, current	45,777	29,810	42,499
Notes payable	164,650	185,620	164,200
Current maturities of long-term debt	5,743	5,743	255,743
Current liabilities held for sale	0	0	24,910
Total current liabilities	591,015	648,230	788,564
Long-term debt	2,950,299	2,950,835	2,858,787
Deferred credits and other liabilities:
Deferred income tax liabilities, net	337,184	311,331	290,491
Regulatory liabilities, non-current	511,482	510,984	495,362
Benefit plan liabilities	145,883	145,147	160,580
Other deferred credits and other liabilities	118,007	109,377	105,221
Total deferred credits and other liabilities	1,112,556	1,076,839	1,051,654
Commitments and contingencies (See Notes 8, 10, 15, 16)
Equity:
Common stock $1 par value; 100,000,000 shares authorized; issued 60,378,020; 60,048,567; and 53,648,817 shares, respectively	60,378	60,049	53,649
Additional paid-in capital	1,469,410	1,450,569	1,151,933
Retained earnings	777,262	700,396	656,161
Treasury stock, at cost – 23,756; 44,253; and 53,959 shares, respectively	(1,432)	(2,510)	(3,049)
Accumulated other comprehensive income (loss)	(26,459)	(26,916)	(39,924)
Total stockholders’ equity	2,279,159	2,181,588	1,818,770
Noncontrolling interest	104,543	105,835	109,214
Total equity	2,383,702	2,287,423	1,927,984
TOTAL LIABILITIES AND TOTAL EQUITY	$ 7,037,572	$ 6,963,327	$ 6,626,989

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Statement of Financial Position [Abstract]
Common Stock, Par Value (usd per share)	$ 1	$ 1	$ 1
Common Stock, Shares Issued	60,378,020	60,048,567	53,648,817
Treasury Stock, Shares	23,756	44,253	53,959
Common Stock, Shares Authorized	100,000,000	100,000,000	100,000,000

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities:
Net income	$ 107,362	$ 136,634
Loss from discontinued operations, net of tax	0	2,343
Income from continuing operations	107,362	138,977
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	51,028	48,590
Deferred financing cost amortization	2,007	1,900
Stock compensation	3,296	2,209
Deferred income taxes	19,602	(25,430)
Employee benefit plans	3,137	3,378
Other adjustments, net	4,428	3,053
Changes in certain operating assets and liabilities:
Materials, supplies and fuel	29,387	31,196
Accounts receivable, unbilled revenues and other operating assets	(15,857)	(25,113)
Accounts payable and other operating liabilities	(41,689)	(71,149)
Regulatory assets - current	13,031	47,903
Regulatory liabilities - current	(1,635)	16,098
Other operating activities, net	1,796	(278)
Net cash provided by operating activities of continuing operations	175,893	171,334
Net cash provided by (used in) operating activities of discontinued operations	0	(1,459)
Net cash provided by operating activities	175,893	169,875
Investing activities:
Property, plant and equipment additions	(144,126)	(69,972)
Purchase of investment	0	(23,500)
Other investing activities	(901)	(261)
Net cash provided by (used in) investing activities of continuing operations	(145,027)	(93,733)
Net cash provided by (used in) investing activities of discontinued operations	0	20,179
Net cash provided by (used in) investing activities	(145,027)	(73,554)
Financing activities:
Dividends paid on common stock	(30,332)	(25,444)
Common stock issued	19,949	372
Net (payments) borrowings of short-term debt	(20,970)	(47,100)
Long-term debt - repayments	(1,436)	(1,436)
Distributions to noncontrolling interest	(4,846)	(5,648)
Other financing activities	(1,657)	(1,400)
Net cash provided by (used in) financing activities	(39,292)	(80,656)
Net change in cash, cash equivalents and restricted cash	(8,426)	15,665
Cash, cash equivalents and restricted cash at beginning of period	24,145	18,240
Cash, cash equivalents and restricted cash at end of period	$ 15,719	$ 33,905

Management's Statement_

Management's Statement:	3 Months Ended
	Mar. 31, 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. Accounting standards for presentation of segments requires an approach based on the way we organize the segments for making operating decisions and how the chief operating decision maker (CODM) assesses performance. We have changed our segment performance metrics and 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 CODM assesses the performance of our segments by using adjusted operating income, which considers the power sales arrangement between Colorado IPP and Colorado Electric be treated as an executory contract. Adjusted operating income adjusts this power sales arrangement from being accounted for as a capital lease to being accounted for as an executory contract on an accrual basis. This adjustment impacts Electric Utilities and Power Generation segments and Corporate and Other. There were no adjustments to Gas Utilities and Mining segments and this adjustment had no effect on our consolidated operating income. 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 profit and adjust revenues, operating income, and total assets for the power sales agreement to an executory contract and not a capital lease. See Notes 2 and 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 of our Oil and Gas segment in 2018. The Oil and Gas segment assets and liabilities have been classified as held for sale and the results of operations are 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 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 March 31, 2019 , December 31, 2018 , and March 31, 2018 financial information and are of a normal recurring nature. 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 months ended March 31, 2019 and March 31, 2018 , and our financial condition as of March 31, 2019 , December 31, 2018 , and March 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. 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. 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.

Revenue_

Revenue:	3 Months Ended
	Mar. 31, 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 months ended March 31, 2019 and 2018 . Sales tax and other similar taxes are excluded from revenues. Three Months Ended March 31, 2019 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer types: (in thousands) Retail $ 153,463 $ 354,275 $ — $ 15,829 $ (8,128 ) $ 515,439 Transportation — 44,517 — — (432 ) 44,085 Wholesale 8,343 — 15,469 — (13,213 ) 10,599 Market - off-system sales 6,692 217 — — (2,224 ) 4,685 Transmission/Other 14,175 13,190 — — (4,203 ) 23,162 Revenue from contracts with customers 182,673 412,199 15,469 15,829 (28,200 ) 597,970 Other revenues 254 (1,119 ) (b) 9,776 600 (9,671 ) (160 ) Total revenues $ 182,927 $ 411,080 $ 25,245 $ 16,429 $ (37,871 ) $ 597,810 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 15,829 $ (8,128 ) $ 7,701 Services transferred over time 182,673 412,199 15,469 — (20,072 ) 590,269 Revenue from contracts with customers $ 182,673 $ 412,199 $ 15,469 $ 15,829 $ (28,200 ) $ 597,970 Three Months Ended March 31, 2018 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer Types: Retail $ 147,057 $ 341,394 $ — $ 16,557 $ (7,842 ) $ 497,166 Transportation — 41,669 — — (409 ) 41,260 Wholesale 9,050 — 14,769 — (13,049 ) 10,770 Market - Off-System Sales 4,144 427 — — (2,522 ) 2,049 Transmission/Other 13,071 12,670 — — (3,631 ) 22,110 Revenue from contracts with customers $ 173,322 $ 396,160 $ 14,769 $ 16,557 $ (27,453 ) $ 573,355 Other Revenues 233 1,184 (b) 9,170 571 (9,124 ) 2,034 Total Revenues $ 173,555 $ 397,344 $ 23,939 $ 17,128 $ (36,577 ) $ 575,389 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 16,557 $ (7,842 ) $ 8,715 Services transferred over time 173,322 396,160 14,769 — (19,611 ) 564,640 Revenue from contracts with customers $ 173,322 $ 396,160 $ 14,769 $ 16,557 $ (27,453 ) $ 573,355 (a) Due to changes to our segment performance measure as disclosed in Note 1, Power Generation Wholesale revenue was recast for the three months ended March 31, 2018 which resulted in a change of $0.8 million . For the three months ended March 31, 2019, the impact to Power Generation Wholesale revenue was $3.4 million . The changes to Power Generation were offset by changes to eliminations in Inter-company Revenues and there was no impact to our consolidated Total Revenues. (b) Other revenues in the Gas Utilities segment include alternative revenue programs related to weather normalization mechanisms for Arkansas Gas and Kansas Gas that are considered out of scope for ASC 606. Contract Balances

Business Segment Information_

Business Segment Information:	3 Months Ended
	Mar. 31, 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. As disclosed in Note 1, changes to our segment performance measure resulted in a revision of the Company’s segment disclosures for all periods to adjust revenues, operating income, and assets related to the power sales arrangement between Colorado IPP and Colorado Electric from being accounted for as a capital lease to being accounted for as an executory contract on an accrual basis. This change had no effect on our consolidated revenues, operating income, or total assets. See below for more information. Segment information and Corporate and Other is as follows (in thousands): Three Months Ended March 31, 2019 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 176,663 $ 254 $ 6,010 $ — $ 182,927 Gas Utilities (a) 411,500 (1,119 ) 699 — 411,080 Power Generation (b) 2,257 436 13,212 9,340 25,245 Mining 7,550 269 8,279 331 16,429 Corporate and Other — — — — — Inter-company eliminations (b) — — (28,200 ) (9,671 ) (37,871 ) Total $ 597,970 $ (160 ) $ — $ — $ 597,810 Three Months Ended March 31, 2018 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 167,178 $ 233 $ 6,144 $ — $ 173,555 Gas Utilities (a) 395,742 1,184 418 — 397,344 Power Generation (b) 1,720 371 13,049 8,799 23,939 Mining 8,715 246 7,842 325 17,128 Corporate and Other — — — — — Inter-company eliminations (b) — — (27,453 ) (9,124 ) (36,577 ) Total $ 573,355 $ 2,034 $ — $ — $ 575,389 (a) Other revenues in the Gas Utilities segment include alternative revenue programs related to weather normalization mechanisms for Arkansas Gas and Kansas Gas that are considered out of scope for ASC 606. (b) Due to changes to our segment performance measure, Power Generation Inter-company Operating Revenue for Contract Customers was recast for the three months ended March 31, 2018 which resulted in a change of $0.8 million . For the three months ended March 31, 2019, the impact to Power Generation Inter-company Operating Revenue for Contract Customers was $3.4 million . The changes to Power Generation were offset by changes to Inter-company eliminations and there was no impact on our consolidated Total revenues. Three Months Ended March 31, 2019 2018 Adjusted operating income: Electric Utilities (a) $ 41,020 $ 38,480 Gas Utilities 103,314 95,443 Power Generation (a) 11,967 11,776 Mining 4,337 4,271 Corporate and Other (a) (507 ) (1,696 ) Operating income 160,131 148,274 Interest expense, net (34,717 ) (34,995 ) Other income (expense), net (789 ) (104 ) Income tax benefit (expense) (b) (17,263 ) 25,802 Income from continuing operations 107,362 138,977 Net (loss) from discontinued operations — (2,343 ) Net income 107,362 136,634 Net income attributable to noncontrolling interest (3,554 ) (3,630 ) Net income available for common stock $ 103,808 $ 133,004 ___________ (a) Due to changes to our segment performance measure, Adjusted operating income was recast for the three months ended March 31, 2018, for Electric Utilities, Power Generation, and Corporate and Other which resulted in changes of $1.7 million , ($1.6) million , and ($0.1) million , respectively. The impact to Adjusted operating income for the three months ended March 31, 2019, for Electric Utilities, Power Generation, and Corporate and Other was ($5.4) million , $0.7 million , and $4.7 million , respectively. There was no impact on our consolidated Operating income. (b) Income tax benefit (expense) for the three months ended March 31, 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: March 31, 2019 December 31, 2018 March 31, 2018 Segment: Electric Utilities (a) $ 2,755,056 $ 2,707,695 $ 2,629,267 Gas Utilities 3,639,430 3,623,475 3,398,473 Power Generation (a) 372,503 342,085 314,764 Mining 63,088 80,594 65,568 Corporate and Other 207,495 209,478 194,193 Discontinued operations — — 24,724 Total assets $ 7,037,572 $ 6,963,327 $ 6,626,989 ___________ (a) Due to changes to our segment performance measure, Electric Utilities Total assets were recast as of December 31, 2018 and March 31, 2018 which resulted in changes of ($188) million and ($261) million , respectively. Power Generation Total Assets were recast as of December 31, 2018, and March 31, 2018 which resulted in changes of $188 million and $261 million , respectively. The impact to Electric Utilities and Power Generation Total Assets as of March 31, 2019, was ($186) million and $186 million , respectively. There was no

Accounts Receivable_

Accounts Receivable:	3 Months Ended
	Mar. 31, 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 March 31, 2019 Receivable, Trade Revenue Doubtful Accounts Receivable, net Electric Utilities $ 45,764 $ 31,075 $ (535 ) $ 76,304 Gas Utilities 138,005 62,566 (4,008 ) 196,563 Power Generation 3,167 — — 3,167 Mining 2,791 — — 2,791 Corporate 3,946 — (169 ) 3,777 Total $ 193,673 $ 93,641 $ (4,712 ) $ 282,602 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 Accounts Unbilled Less Allowance for Accounts March 31, 2018 Receivable, Trade Revenue Doubtful Accounts Receivable, net Electric Utilities $ 40,492 $ 33,907 $ (624 ) $ 73,775 Gas Utilities 120,910 60,142 (3,684 ) 177,368 Power Generation 1,580 — — 1,580 Mining 3,133 — — 3,133 Corporate 1,916 — — 1,916 Total $ 168,031 $ 94,049 $ (4,308 ) $ 257,772

Regulatory Accounting_

Regulatory Accounting:	3 Months Ended
	Mar. 31, 2019
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Accounting	REGULATORY ACCOUNTING We had the following regulatory assets and liabilities (in thousands) as of: March 31, 2019 December 31, 2018 March 31, 2018 Regulatory assets Deferred energy and fuel cost adjustments (a) $ 35,512 $ 29,661 $ 25,056 Deferred gas cost adjustments (a) 5,124 3,362 2,118 Gas price derivatives (a) 3,939 6,201 11,045 Deferred taxes on AFUDC (b) 7,771 7,841 7,808 Employee benefit plans (c) 111,724 110,524 109,999 Environmental (a) 945 959 1,012 Loss on reacquired debt (a) 20,570 21,001 20,267 Renewable energy standard adjustment (a) 1,533 1,722 1,600 Deferred taxes on flow through accounting (c) 33,226 31,044 28,014 Decommissioning costs (b) 11,694 11,700 12,552 Gas supply contract termination (a) 12,866 14,310 18,590 Other regulatory assets (a) 41,803 45,910 29,171 Total regulatory assets 286,707 284,235 267,232 Less current regulatory assets (54,303 ) (48,776 ) (54,492 ) Regulatory assets, non-current $ 232,404 $ 235,459 $ 212,740 Regulatory liabilities Deferred energy and gas costs (a) $ 19,018 $ 6,991 $ 20,194 Employee benefit plan costs and related deferred taxes (c) 42,207 42,533 40,332 Cost of removal (a) 154,170 150,123 139,002 Excess deferred income taxes (c) 307,894 310,562 310,622 TCJA revenue reserve 16,549 18,032 15,239 Other regulatory liabilities (c) 17,421 12,553 12,472 Total regulatory liabilities 557,259 540,794 537,861 Less current regulatory liabilities (45,777 ) (29,810 ) (42,499 ) Regulatory liabilities, non-current $ 511,482 $ 510,984 $ 495,362 __________ (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 Nebraska On March 29, 2019, Nebraska Gas filed an application with the NPSC requesting to merge its two gas distribution utilities into a new public utility entity. The filing also requests to merge the terms and conditions of the existing tariffs of the two utilities into a single tariff. Wyoming On March 6, 2019, Wyoming Gas filed an application with the WPSC requesting to merge its four gas distribution utilities into a new public utility entity. The filing also requests the new entity adopt the terms and conditions of the existing tariffs. Colorado On February 1, 2019, Colorado Gas filed a rate review with the CPUC requesting approval to consolidate the base rate areas, tariffs, terms and conditions and adjustment clauses of its two legacy utilities. The rate review also requests $2.5 million

Materials, Supplies and Fuel_

Materials, Supplies and Fuel:	3 Months Ended
	Mar. 31, 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: March 31, 2019 December 31, 2018 March 31, 2018 Materials and supplies $ 76,728 $ 75,081 $ 72,045 Fuel - Electric Utilities 2,485 2,850 2,903 Natural gas in storage held for distribution 8,463 39,368 7,097 Total materials, supplies and fuel $ 87,676 $ 117,299 $ 82,045

Earnings Per Share_

Earnings Per Share:	3 Months Ended
	Mar. 31, 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 March 31, 2019 2018 Net income available for common stock $ 103,808 $ 133,004 Weighted average shares - basic 59,920 53,319 Dilutive effect of: Equity Units (a) — 733 Equity compensation 140 70 Weighted average shares - diluted 60,060 54,122 __________ (a) Calculated using the treasury stock method. On November 1, 2018, we completed settlement of the stock purchase contracts that are 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 March 31, 2019 2018 Equity compensation 6 71 Anti-dilutive shares 6 71

Notes Payable, Current Maturiti

Notes Payable, Current Maturities and Debt:	3 Months Ended
	Mar. 31, 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: March 31, 2019 December 31, 2018 March 31, 2018 Balance Outstanding Letters of Credit Balance Outstanding Letters of Credit Balance Outstanding Letters of Credit Revolving Credit Facility $ — $ 14,006 $ — $ 22,310 $ — $ 15,830 CP Program 164,650 — 185,620 — 164,200 — Total $ 164,650 $ 14,006 $ 185,620 $ 22,310 $ 164,200 $ 15,830 Revolving Credit Facility and CP Program On July 30, 2018, we amended and restated our corporate Revolving Credit Facility, maintaining total commitments of $750 million and extending the term through July 30, 2023 with two one year extension options (subject to consent from lenders). This facility is similar to the former revolving credit facility, which includes an accordion feature that allows us, with the consent of the administrative agent, the issuing agents and each bank increasing or providing a new commitment, to increase total commitments up to $1.0 billion . Borrowings continue to be available under a base rate or various Eurodollar rate options. 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 March 31, 2019 . Based on our credit ratings, a 0.175% commitment fee was charged on the unused amount at March 31, 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 payments under the CP Program during the three months ended March 31, 2019 were $21 million and our notes outstanding as of March 31, 2019 were $165 million . As of March 31, 2019 , the weighted average interest rate on CP Program borrowings was 2.70% . As of March 31, 2019 , we had outstanding letters of credit of totaling approximately $14 million . 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. Our Revolving Credit Facility and term loans require compliance with the following financial covenant at the end of each quarter: As of March 31, 2019 Covenant Requirement Consolidated Indebtedness to Capitalization Ratio 58.1% Less than 65% As of March 31, 2019

Equity_

Equity:	3 Months Ended
	Mar. 31, 2019
Statement of Stockholders' Equity [Abstract]
Equity	EQUITY A summary of the changes in equity is as follows: Three Months Ended March 31, 2019 Common Stock Treasury Stock (in thousands except share amounts) Shares Value Shares Value Additional Paid in Capital Retained Earnings AOCI Non controlling Interest Total December 31, 2018 60,048,567 $ 60,049 44,253 $ (2,510 ) $ 1,450,569 $ 700,396 $ (26,916 ) $ 105,835 $ 2,287,423 Net income (loss) available for common stock — — — — — 103,808 — 3,554 107,362 Other comprehensive income (loss), net of tax — — — — — — 457 — 457 Dividends on common stock ($0.505 per share) — — — — — (30,332 ) — — (30,332 ) Share-based compensation 48,956 49 (20,497 ) 1,078 (589 ) — — — 538 Issuance of common stock 280,497 280 — — 19,719 — — — 19,999 Issuance costs — — — — (289 ) — — — (289 ) Cumulative effect of ASU 2016-02, Leases implementation — — — — — 3,390 — — 3,390 Distributions to noncontrolling interest — — — — — — — (4,846 ) (4,846 ) March 31, 2019 60,378,020 $ 60,378 23,756 $ (1,432 ) $ 1,469,410 $ 777,262 $ (26,459 ) $ 104,543 $ 2,383,702 Three Months Ended March 31, 2018 Common Stock Treasury Stock (in thousands except share amounts) Shares Value Shares Value Additional Paid in Capital Retained Earnings AOCI Non controlling Interest Total December 31, 2017 53,579,986 $ 53,580 39,064 $ (2,306 ) $ 1,150,285 $ 548,617 $ (41,202 ) $ 111,232 $ 1,820,206 Net income (loss) available for common stock — — — — — 133,004 — 3,630 136,634 Other comprehensive income (loss), net of tax — — — — — — 1,260 — 1,260 Dividends on common stock ($0.475 per share) — — — — — (25,444 ) — — (25,444 ) Share-based compensation 64,770 65 14,895 (743 ) 1,433 — — — 755 Dividend reinvestment and stock purchase plan 4,061 4 — — 215 — — — 219 Other stock transactions — — — — — (16 ) 18 — 2 Distributions to noncontrolling interest — — — — — — — (5,648 ) (5,648 ) March 31, 2018 53,648,817 $ 53,649 53,959 $ (3,049 ) $ 1,151,933 $ 656,161 $ (39,924 ) $ 109,214 $ 1,927,984 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 March 31, 2019, we issued a total of 280,497 shares of common stock under the ATM equity offering program for $20 million , net of $0.2 million

Risk Management Activities_

Risk Management Activities:	3 Months Ended
	Mar. 31, 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 guarantees, 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 April 2019 through May 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: March 31, 2019 December 31, 2018 March 31, 2018 Notional (MMBtus) Maximum Term (months) (a) Notional (MMBtus) Maximum Term (months) (a) Notional (MMBtus) Maximum Term (months) (a) Natural gas futures purchased 3,120,000 21 4,000,000 24 6,760,000 33 Natural gas options purchased, net 1,150,000 10 4,320,000 13 170,000 11 Natural gas basis swaps purchased 3,020,000 21 3,960,000 24 6,770,000 33 Natural gas over-the-counter swaps, net (b) 3,316,000 26 3,660,000 24 2,760,000 26 Natural gas physical contracts, net (c) 2,786,980 12 18,325,852 30 386,250 32 __________ (a) Term reflects the maximum forward period hedged. (b) As of March 31, 2019 , 534,000 MMBtus were designated as cash flow hedges. (c) Volumes exclude contracts that qualify for the normal purchase, normal sales exception. Based on March 31, 2019 prices, a $0.1 million loss 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 March 31, 2019 , the Company posted $0.2 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 months ended March 31, 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 March 31, 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 554 Total $ (159 ) Three Months Ended March 31, 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 $ (713 ) Commodity derivatives Fuel, purchased power and cost of natural gas sold (621 ) Total $ (1,334 ) 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 months ended March 31, 2019 and 2018 . Three Months Ended March 31, 2019 2018 (in thousands) Increase (decrease) in fair value: Forward commodity contracts $ 234 $ (297 ) Recognition of (gains) losses in earnings due to settlements: Interest rate swaps 713 713 Forward commodity contracts (554 ) 621 Total other comprehensive income (loss) from hedging $ 393 $ 1,037 Derivatives Not Designated as Hedge Instruments The following table summarizes the impacts of derivative instruments not designated as hedge instruments on our Condensed Consolidated Statements of Income for the three months ended March 31, 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 March 31, 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 $ 25 $ 254 $ 25 $ 254 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 assets or Regulatory liability accounts related to the hedges in our utilities were $3.9 million , $6.2 million and $11 million at March 31, 2019 , December 31, 2018 and March 31, 2018

Fair Value Measurements_

Fair Value Measurements:	3 Months Ended
	Mar. 31, 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 component 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. Recurring Fair Value Measurements As of March 31, 2019 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting Total (in thousands) Assets: Commodity derivatives — Utilities $ — $ 1,375 $ — $ (388 ) $ 987 Total $ — $ 1,375 $ — $ (388 ) $ 987 Liabilities: Commodity derivatives — Utilities $ — $ 4,122 $ — $ (4,009 ) $ 113 Total $ — $ 4,122 $ — $ (4,009 ) $ 113 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 As of March 31, 2018 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting Total (in thousands) Assets: Commodity derivatives — Utilities $ — $ 414 $ — $ (119 ) $ 295 Total $ — $ 414 $ — $ (119 ) $ 295 Liabilities: Commodity derivatives — Utilities $ — $ 12,259 $ — $ (11,175 ) $ 1,084 Total $ — $ 12,259 $ — $ (11,175 ) $ 1,084 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 March 31, 2019 December 31, 2018 March 31, 2018 Derivatives designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets — current $ 131 $ 415 $ — Noncurrent commodity derivatives Other assets, non-current 9 18 — Liability derivative instruments: Current commodity derivatives Derivative liabilities — current (11 ) (114 ) (394 ) Noncurrent commodity derivatives Other deferred credits and other liabilities — (4 ) (29 ) Total derivatives designated as hedges $ 129 $ 315 $ (423 ) Derivatives not designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets — current $ 801 $ 1,085 $ 295 Noncurrent commodity derivatives Other assets, non-current 46 1 — Liability derivative instruments: Current commodity derivatives Derivative liabilities — current (84 ) (833 ) (497 ) Noncurrent commodity derivatives Other deferred credits and other liabilities (18 ) (56 ) (164 ) Total derivatives not designated as hedges $ 745 $ 197 $ (366 ) 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

Fair Value of Financial Instrum

Fair Value of Financial Instruments:	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	FAIR VALUE OF FINANCIAL INSTRUMENTS The estimated fair values of our financial instruments, excluding derivatives which are presented in Note 11 , were as follows (in thousands) as of: March 31, 2019 December 31, 2018 March 31, 2018 Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value Cash and cash equivalents (a) $ 12,225 $ 12,225 $ 20,776 $ 20,776 $ 30,947 $ 30,947 Restricted cash (a) $ 3,494 $ 3,494 $ 3,369 $ 3,369 $ 2,958 $ 2,958 Notes payable (b) $ 164,650 $ 164,650 $ 185,620 $ 185,620 $ 164,200 $ 164,200 Long-term debt, including current maturities (c) (d) $ 2,956,042 $ 3,137,538 $ 2,956,578 $ 3,039,108 $ 3,114,530 $ 3,265,965 __________ (a) Carrying value approximates fair value due to either the short-term length of maturity or variable interest rates that approximate prevailing market rates, and therefore is classified in Level 1 in the fair value hierarchy. (b) Notes payable consist of commercial paper borrowings and borrowings on our Revolving Credit Facility. Carrying value approximates fair value due to the short-term length of maturity; since these borrowings are not traded on an exchange, they are classified in Level 2 in the fair value hierarchy. (c) 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. (d)

Other Comprehensive Income (Los

Other Comprehensive Income (Loss):	3 Months Ended
	Mar. 31, 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, net of tax (in thousands): Location on the Condensed Consolidated Statements of Income Amount Reclassified from AOCI Three Months Ended March 31, 2019 March 31, 2018 Gains and (losses) on cash flow hedges: Interest rate swaps Interest expense $ (713 ) $ (713 ) Commodity contracts Fuel, purchased power and cost of natural gas sold 554 (621 ) (159 ) (1,334 ) Income tax Income tax benefit (expense) 35 297 Total reclassification adjustments related to cash flow hedges, net of tax $ (124 ) $ (1,037 ) Amortization of components of defined benefit plans: Prior service cost Operations and maintenance $ 19 $ 45 Actuarial gain (loss) Operations and maintenance (220 ) (622 ) (201 ) (577 ) Income tax Income tax benefit (expense) 48 126 Total reclassification adjustments related to defined benefit plans, net of tax $ (153 ) $ (451 ) Total reclassifications $ (277 ) $ (1,488 ) 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 — 180 — 180 Amounts reclassified from AOCI 550 (426 ) 153 277 As of March 31, 2019 $ (16,757 ) $ 82 $ (9,784 ) $ (26,459 ) Interest Rate Swaps Commodity Derivatives Employee Benefit Plans Total Balance as of December 31, 2017 $ (19,581 ) $ (518 ) $ (21,103 ) $ (41,202 ) Other comprehensive income (loss) before reclassifications — (228 ) — (228 ) Amounts reclassified from AOCI 561 476 451 1,488 Reclassifications of certain tax effects from AOCI 15 — 3 18 As of March 31, 2018 $ (19,005 ) $ (270 ) $ (20,649 ) $ (39,924 )

Supplemental Disclosure of Cash

Supplemental Disclosure of Cash Flow Information:	3 Months Ended
	Mar. 31, 2019
Supplemental Cash Flow Information [Abstract]
Supplemental Disclosure of Cash Flow Information	SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION Three Months Ended March 31, 2019 March 31, 2018 (in thousands) Non-cash investing and financing activities — Property, plant and equipment acquired with accrued liabilities $ 56,571 $ 21,708 Cash (paid) refunded during the period — Interest (net of amounts capitalized) $ (30,672 ) $ (36,928 ) Income taxes $ 8 $ (14,336 )

Employee Benefit Plans_

Employee Benefit Plans:	3 Months Ended
	Mar. 31, 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 March 31, 2019 2018 Service cost $ 1,346 $ 1,708 Interest cost 4,343 3,867 Expected return on plan assets (6,100 ) (6,185 ) Prior service cost 6 15 Net loss (gain) 941 2,158 Net periodic benefit cost $ 536 $ 1,563 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 March 31, 2019 2018 Service cost $ 454 $ 573 Interest cost 560 521 Expected return on plan assets (57 ) (57 ) Prior service cost (benefit) (99 ) (99 ) Net loss (gain) — 54 Net periodic benefit cost $ 858 $ 992 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans The components of net periodic benefit cost for the Supplemental Non-qualified Defined Benefit and Defined Contribution Plans were as follows (in thousands): Three Months Ended March 31, 2019 2018 Service cost (a) $ 1,285 $ 280 Interest cost 324 293 Net loss (gain) 134 250 Net periodic benefit cost $ 1,743 $ 823 __________ (a) The increase in service cost for the three months ended March 31, 2019 compared to the same period in 2018 is primarily driven by market returns. 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 Additional Contributions Contributions Three Months Ended March 31, 2019 Anticipated for 2019 Anticipated for 2020 Defined Benefit Pension Plan $ — $ 12,700 $ 12,700 Non-pension Defined Benefit Postretirement Healthcare Plans $ 1,109 $ 3,326 $ 4,271 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans $ 366 $ 1,097 $ 1,562

Commitments and Contingencies_

Commitments and Contingencies:	3 Months Ended
	Mar. 31, 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. Dividend Restrictions Our Revolving Credit Facility and other debt obligations contain restrictions on the payment of cash dividends upon a default or event of default. As of March 31, 2019 , we were in compliance with the debt covenants. Due to our holding company structure, substantially all of our operating cash flows are provided by dividends paid or distributions made by our subsidiaries. The cash to pay dividends to our stockholders is derived from these cash flows. As a result, certain statutory limitations or regulatory or financing agreements could affect the levels of distributions allowed to be made by our subsidiaries. Our utilities are generally limited in the amount of dividends allowed to be paid to us as a utility holding company under the Federal Power Act and settlement agreements with state regulatory jurisdictions and financing agreements. As of March 31, 2019 , the restricted net assets at our Electric Utilities and Gas Utilities were approximately $257 million

Discontinued Operations_

Discontinued Operations:	3 Months Ended
	Mar. 31, 2019
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations	DISCONTINUED OPERATIONS Results of operations for discontinued operations have been classified as Loss from discontinued operations, net of income taxes in the accompanying Condensed Consolidated Statements of Income. Assets and liabilities of the discontinued operations have been reclassified and reflected on the accompanying Condensed Consolidated Balance Sheets as “Current assets held for sale” and “Current liabilities held for sale”, respectively. Prior periods relating to our discontinued operations have also been 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 of our Oil and Gas segment in 2018. Total assets and liabilities of our Oil and Gas segment at March 31, 2018 were classified as Current assets held for sale and Current liabilities held for sale on the accompanying Condensed Consolidated Balance Sheets due to the final disposals occurring in 2018. As of (in thousands) March 31, 2018 Other current assets $ 4,332 Deferred income tax assets, noncurrent, net 3,739 Property, plant and equipment, net 16,653 Other current liabilities (17,233 ) Other noncurrent liabilities (7,677 ) Net (liabilities) $ (186 )

Income Taxes_

Income Taxes:	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES Income tax benefit (expense), net for the three months ended March 31, 2019 was $(17) million compared to $26 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 $2.3 million income tax expense associated with changes in the prior estimated impact of tax reform on deferred income taxes; and ◦ A current year $3.4 million increase in income tax benefit from forecasted federal production tax credits and state investment tax credits as well as $1.8 million of income tax benefit for deferred tax amortization related to tax reform (which is offset by reduced revenue at our utilities). Prior year tax benefit related to legal restructuring As part of the Company’s ongoing efforts to continue to integrate the legal entities that the Company acquired in recent years, certain legal entity restructuring transactions occurred on March 31, 2018. As a result of these transactions, $49 million of deferred income tax assets, related to goodwill that is amortizable for tax purposes, were recorded and deferred tax benefits of $49 million were recorded to Income tax benefit (expense) on the Condensed Consolidated Statements of Income. Due to this being a common control transaction, it had no effect on the other assets and liabilities of these entities. Prior year TCJA expense On December 22, 2017, the TCJA was signed into law reducing the federal corporate rate from 35% to 21% effective January 1, 2018. During the three months ended March 31, 2018, we recorded approximately $2.3 million

Accrued Liabilities_

Accrued Liabilities:	3 Months Ended
	Mar. 31, 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: March 31, 2019 December 31, 2018 March 31, 2018 Accrued employee compensation, benefits and withholdings $ 48,078 $ 63,742 $ 46,262 Accrued property taxes 43,662 42,510 42,912 Customer deposits and prepayments 39,125 43,574 35,748 Accrued interest and contract adjustment payments 35,149 31,759 30,426 CIAC current portion 1,485 1,485 1,552 Other (none of which is individually significant) 28,573 32,431 37,140 Total accrued liabilities $ 196,072 $ 215,501 $ 194,040

Leases_

Leases:	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Lessee, Operating 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 lease 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 March 31, 2019 Operating lease cost Operations and maintenance $ 311 Finance lease cost: Amortization of right-of-use asset Depreciation, depletion and amortization 17 Interest on lease liabilities Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) 3 Total lease cost $ 331 Supplemental balance sheet information related to leases was as follows (in thousands): Balance Sheet Location As of March 31, 2019 Assets: Operating lease assets Other assets, non-current $ 5,331 Finance lease assets Other assets, non-current 481 Total lease assets $ 5,812 Liabilities: Current: Operating leases Accrued liabilities $ 974 Finance leases Accrued liabilities 92 Noncurrent: Operating leases Other deferred credits and other liabilities 4,563 Finance leases Other deferred credits and other liabilities 391 Total lease liabilities $ 6,020 Supplemental cash flow information related to leases was as follows (in thousands): Three Months Ended March 31, 2019 Cash paid included in the measurement of lease liabilities: Operating cash flows from operating leases $ 246 Operating cash flows from finance lease $ 3 Financing cash flows from finance lease $ 15 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ 2,328 Finance leases $ — As of March 31, 2019 Weighted average remaining lease term (years): Operating leases 8 years Finance leases 5 years Weighted average discount rate: Operating leases 4.23 % Finance leases 4.21 % As of March 31, 2019 , scheduled maturities of lease liabilities for future years were as follows (in thousands): Operating Leases Finance Leases Total 2019 (a) $ 952 $ 83 $ 1,035 2020 936 111 1,047 2021 820 111 931 2022 698 111 809 2023 699 110 809 Thereafter 2,653 9 2,662 Total lease payments (b) $ 6,758 $ 535 $ 7,293 Less imputed interest 1,221 52 1,273 Present value of lease liabilities $ 5,537 $ 483 $ 6,020 (a) Includes lease liabilities for the remaining nine 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
Lessee, Finance 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 lease 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 March 31, 2019 Operating lease cost Operations and maintenance $ 311 Finance lease cost: Amortization of right-of-use asset Depreciation, depletion and amortization 17 Interest on lease liabilities Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) 3 Total lease cost $ 331 Supplemental balance sheet information related to leases was as follows (in thousands): Balance Sheet Location As of March 31, 2019 Assets: Operating lease assets Other assets, non-current $ 5,331 Finance lease assets Other assets, non-current 481 Total lease assets $ 5,812 Liabilities: Current: Operating leases Accrued liabilities $ 974 Finance leases Accrued liabilities 92 Noncurrent: Operating leases Other deferred credits and other liabilities 4,563 Finance leases Other deferred credits and other liabilities 391 Total lease liabilities $ 6,020 Supplemental cash flow information related to leases was as follows (in thousands): Three Months Ended March 31, 2019 Cash paid included in the measurement of lease liabilities: Operating cash flows from operating leases $ 246 Operating cash flows from finance lease $ 3 Financing cash flows from finance lease $ 15 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ 2,328 Finance leases $ — As of March 31, 2019 Weighted average remaining lease term (years): Operating leases 8 years Finance leases 5 years Weighted average discount rate: Operating leases 4.23 % Finance leases 4.21 % As of March 31, 2019 , scheduled maturities of lease liabilities for future years were as follows (in thousands): Operating Leases Finance Leases Total 2019 (a) $ 952 $ 83 $ 1,035 2020 936 111 1,047 2021 820 111 931 2022 698 111 809 2023 699 110 809 Thereafter 2,653 9 2,662 Total lease payments (b) $ 6,758 $ 535 $ 7,293 Less imputed interest 1,221 52 1,273 Present value of lease liabilities $ 5,537 $ 483 $ 6,020 (a) Includes lease liabilities for the remaining nine 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, Operating 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 lease 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 March 31, 2019 Operating lease cost Operations and maintenance $ 311 Finance lease cost: Amortization of right-of-use asset Depreciation, depletion and amortization 17 Interest on lease liabilities Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) 3 Total lease cost $ 331 Supplemental balance sheet information related to leases was as follows (in thousands): Balance Sheet Location As of March 31, 2019 Assets: Operating lease assets Other assets, non-current $ 5,331 Finance lease assets Other assets, non-current 481 Total lease assets $ 5,812 Liabilities: Current: Operating leases Accrued liabilities $ 974 Finance leases Accrued liabilities 92 Noncurrent: Operating leases Other deferred credits and other liabilities 4,563 Finance leases Other deferred credits and other liabilities 391 Total lease liabilities $ 6,020 Supplemental cash flow information related to leases was as follows (in thousands): Three Months Ended March 31, 2019 Cash paid included in the measurement of lease liabilities: Operating cash flows from operating leases $ 246 Operating cash flows from finance lease $ 3 Financing cash flows from finance lease $ 15 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ 2,328 Finance leases $ — As of March 31, 2019 Weighted average remaining lease term (years): Operating leases 8 years Finance leases 5 years Weighted average discount rate: Operating leases 4.23 % Finance leases 4.21 % As of March 31, 2019 , scheduled maturities of lease liabilities for future years were as follows (in thousands): Operating Leases Finance Leases Total 2019 (a) $ 952 $ 83 $ 1,035 2020 936 111 1,047 2021 820 111 931 2022 698 111 809 2023 699 110 809 Thereafter 2,653 9 2,662 Total lease payments (b) $ 6,758 $ 535 $ 7,293 Less imputed interest 1,221 52 1,273 Present value of lease liabilities $ 5,537 $ 483 $ 6,020 (a) Includes lease liabilities for the remaining nine 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 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 March 31, 2019 Operating lease income Revenue $ 638 As of March 31, 2019 , scheduled maturities of lease receivables for future years were as follows (in thousands): Operating Leases 2019 (a) $ 1,652 2020 2,010 2021 1,843 2022 1,793 2023 1,799 Thereafter 55,481 Total lease receivables $ 64,578 (a) Includes lease receivables for the remaining nine months of 2019

Management's Statement (Policie

Management's Statement (Policies)	3 Months Ended
	Mar. 31, 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. Accounting standards for presentation of segments requires an approach based on the way we organize the segments for making operating decisions and how the chief operating decision maker (CODM) assesses performance. We have changed our segment performance metrics and 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 CODM assesses the performance of our segments by using adjusted operating income, which considers the power sales arrangement between Colorado IPP and Colorado Electric be treated as an executory contract. Adjusted operating income adjusts this power sales arrangement from being accounted for as a capital lease to being accounted for as an executory contract on an accrual basis. This adjustment impacts Electric Utilities and Power Generation segments and Corporate and Other. There were no adjustments to Gas Utilities and Mining segments and this adjustment had no effect on our consolidated operating income. 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 profit and adjust revenues, operating income, and total assets for the power sales agreement to an executory contract and not a capital lease. See Notes 2 and 3 for more information.
Use of Estimates and Basis of Presentation	Use of Estimates and Basis of Presentation The information furnished in the accompanying Condensed Consolidated Financial Statements reflects certain estimates required and all adjustments, including accruals, which are, in the opinion of management, necessary for a fair presentation of the March 31, 2019 , December 31, 2018 , and March 31, 2018 financial information and are of a normal recurring nature. 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 months ended March 31, 2019 and March 31, 2018 , and our financial condition as of March 31, 2019 , December 31, 2018 , and March 31, 2018
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. 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. 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.
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 months ended March 31, 2019 and 2018 . Sales tax and other similar taxes are excluded from revenues. Three Months Ended March 31, 2019 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer types: (in thousands) Retail $ 153,463 $ 354,275 $ — $ 15,829 $ (8,128 ) $ 515,439 Transportation — 44,517 — — (432 ) 44,085 Wholesale 8,343 — 15,469 — (13,213 ) 10,599 Market - off-system sales 6,692 217 — — (2,224 ) 4,685 Transmission/Other 14,175 13,190 — — (4,203 ) 23,162 Revenue from contracts with customers 182,673 412,199 15,469 15,829 (28,200 ) 597,970 Other revenues 254 (1,119 ) (b) 9,776 600 (9,671 ) (160 ) Total revenues $ 182,927 $ 411,080 $ 25,245 $ 16,429 $ (37,871 ) $ 597,810 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 15,829 $ (8,128 ) $ 7,701 Services transferred over time 182,673 412,199 15,469 — (20,072 ) 590,269 Revenue from contracts with customers $ 182,673 $ 412,199 $ 15,469 $ 15,829 $ (28,200 ) $ 597,970 Three Months Ended March 31, 2018 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer Types: Retail $ 147,057 $ 341,394 $ — $ 16,557 $ (7,842 ) $ 497,166 Transportation — 41,669 — — (409 ) 41,260 Wholesale 9,050 — 14,769 — (13,049 ) 10,770 Market - Off-System Sales 4,144 427 — — (2,522 ) 2,049 Transmission/Other 13,071 12,670 — — (3,631 ) 22,110 Revenue from contracts with customers $ 173,322 $ 396,160 $ 14,769 $ 16,557 $ (27,453 ) $ 573,355 Other Revenues 233 1,184 (b) 9,170 571 (9,124 ) 2,034 Total Revenues $ 173,555 $ 397,344 $ 23,939 $ 17,128 $ (36,577 ) $ 575,389 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 16,557 $ (7,842 ) $ 8,715 Services transferred over time 173,322 396,160 14,769 — (19,611 ) 564,640 Revenue from contracts with customers $ 173,322 $ 396,160 $ 14,769 $ 16,557 $ (27,453 ) $ 573,355 (a) Due to changes to our segment performance measure as disclosed in Note 1, Power Generation Wholesale revenue was recast for the three months ended March 31, 2018 which resulted in a change of $0.8 million . For the three months ended March 31, 2019, the impact to Power Generation Wholesale revenue was $3.4 million . The changes to Power Generation were offset by changes to eliminations in Inter-company Revenues and there was no impact to our consolidated Total Revenues. (b) Other revenues in the Gas Utilities segment include alternative revenue programs related to weather normalization mechanisms for Arkansas Gas and Kansas Gas that are considered out of scope for ASC 606. Contract Balances

Revenue (Tables)

Revenue (Tables)	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	Three Months Ended March 31, 2019 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer types: (in thousands) Retail $ 153,463 $ 354,275 $ — $ 15,829 $ (8,128 ) $ 515,439 Transportation — 44,517 — — (432 ) 44,085 Wholesale 8,343 — 15,469 — (13,213 ) 10,599 Market - off-system sales 6,692 217 — — (2,224 ) 4,685 Transmission/Other 14,175 13,190 — — (4,203 ) 23,162 Revenue from contracts with customers 182,673 412,199 15,469 15,829 (28,200 ) 597,970 Other revenues 254 (1,119 ) (b) 9,776 600 (9,671 ) (160 ) Total revenues $ 182,927 $ 411,080 $ 25,245 $ 16,429 $ (37,871 ) $ 597,810 Timing of revenue recognition: Services transferred at a point in time $ — $ — $ — $ 15,829 $ (8,128 ) $ 7,701 Services transferred over time 182,673 412,199 15,469 — (20,072 ) 590,269 Revenue from contracts with customers $ 182,673 $ 412,199 $ 15,469 $ 15,829 $ (28,200 ) $ 597,970 Three Months Ended March 31, 2018 Electric Utilities Gas Utilities Power Generation (a) Mining Inter-company Revenues (a) Total Customer Types: Retail $ 147,057 $ 341,394 $ — $ 16,557 $ (7,842 ) $ 497,166 Transportation — 41,669 — — (409 ) 41,260 Wholesale 9,050 — 14,769 — (13,049 ) 10,770 Market - Off-System Sales 4,144 427 — — (2,522 ) 2,049 Transmission/Other 13,071 12,670 — — (3,631 ) 22,110 Revenue from contracts with customers $ 173,322 $ 396,160 $ 14,769 $ 16,557 $ (27,453 ) $ 573,355 Other Revenues 233 1,184 (b) 9,170 571 (9,124 ) 2,034 Total Revenues $ 173,555 $ 397,344 $ 23,939 $ 17,128 $ (36,577 ) $ 575,389 Timing of Revenue Recognition: Services transferred at a point in time $ — $ — $ — $ 16,557 $ (7,842 ) $ 8,715 Services transferred over time 173,322 396,160 14,769 — (19,611 ) 564,640 Revenue from contracts with customers $ 173,322 $ 396,160 $ 14,769 $ 16,557 $ (27,453 ) $ 573,355

Business Segment Information (T

Business Segment Information (Tables)	3 Months Ended
	Mar. 31, 2019
Segment Reporting Information, Additional Information [Abstract]
Segment Reporting	Three Months Ended March 31, 2019 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 176,663 $ 254 $ 6,010 $ — $ 182,927 Gas Utilities (a) 411,500 (1,119 ) 699 — 411,080 Power Generation (b) 2,257 436 13,212 9,340 25,245 Mining 7,550 269 8,279 331 16,429 Corporate and Other — — — — — Inter-company eliminations (b) — — (28,200 ) (9,671 ) (37,871 ) Total $ 597,970 $ (160 ) $ — $ — $ 597,810 Three Months Ended March 31, 2018 External Operating Revenue Inter-company Operating Revenue Total Revenues Contract Customers Other Revenues Contract Customers Other Revenues Segment: Electric Utilities $ 167,178 $ 233 $ 6,144 $ — $ 173,555 Gas Utilities (a) 395,742 1,184 418 — 397,344 Power Generation (b) 1,720 371 13,049 8,799 23,939 Mining 8,715 246 7,842 325 17,128 Corporate and Other — — — — — Inter-company eliminations (b) — — (27,453 ) (9,124 ) (36,577 ) Total $ 573,355 $ 2,034 $ — $ — $ 575,389 (a) Other revenues in the Gas Utilities segment include alternative revenue programs related to weather normalization mechanisms for Arkansas Gas and Kansas Gas that are considered out of scope for ASC 606. (b) Due to changes to our segment performance measure, Power Generation Inter-company Operating Revenue for Contract Customers was recast for the three months ended March 31, 2018 which resulted in a change of $0.8 million . For the three months ended March 31, 2019, the impact to Power Generation Inter-company Operating Revenue for Contract Customers was $3.4 million . The changes to Power Generation were offset by changes to Inter-company eliminations and there was no impact on our consolidated Total revenues. Three Months Ended March 31, 2019 2018 Adjusted operating income: Electric Utilities (a) $ 41,020 $ 38,480 Gas Utilities 103,314 95,443 Power Generation (a) 11,967 11,776 Mining 4,337 4,271 Corporate and Other (a) (507 ) (1,696 ) Operating income 160,131 148,274 Interest expense, net (34,717 ) (34,995 ) Other income (expense), net (789 ) (104 ) Income tax benefit (expense) (b) (17,263 ) 25,802 Income from continuing operations 107,362 138,977 Net (loss) from discontinued operations — (2,343 ) Net income 107,362 136,634 Net income attributable to noncontrolling interest (3,554 ) (3,630 ) Net income available for common stock $ 103,808 $ 133,004 ___________ (a) Due to changes to our segment performance measure, Adjusted operating income was recast for the three months ended March 31, 2018, for Electric Utilities, Power Generation, and Corporate and Other which resulted in changes of $1.7 million , ($1.6) million , and ($0.1) million
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: March 31, 2019 December 31, 2018 March 31, 2018 Segment: Electric Utilities (a) $ 2,755,056 $ 2,707,695 $ 2,629,267 Gas Utilities 3,639,430 3,623,475 3,398,473 Power Generation (a) 372,503 342,085 314,764 Mining 63,088 80,594 65,568 Corporate and Other 207,495 209,478 194,193 Discontinued operations — — 24,724 Total assets $ 7,037,572 $ 6,963,327 $ 6,626,989 ___________ (a) Due to changes to our segment performance measure, Electric Utilities Total assets were recast as of December 31, 2018 and March 31, 2018 which resulted in changes of ($188) million and ($261) million , respectively. Power Generation Total Assets were recast as of December 31, 2018, and March 31, 2018 which resulted in changes of $188 million and $261 million , respectively. The impact to Electric Utilities and Power Generation Total Assets as of March 31, 2019, was ($186) million and $186 million , respectively. There was no

Accounts Receivable (Tables)

Accounts Receivable (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2019 Receivable, Trade Revenue Doubtful Accounts Receivable, net Electric Utilities $ 45,764 $ 31,075 $ (535 ) $ 76,304 Gas Utilities 138,005 62,566 (4,008 ) 196,563 Power Generation 3,167 — — 3,167 Mining 2,791 — — 2,791 Corporate 3,946 — (169 ) 3,777 Total $ 193,673 $ 93,641 $ (4,712 ) $ 282,602 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 Accounts Unbilled Less Allowance for Accounts March 31, 2018 Receivable, Trade Revenue Doubtful Accounts Receivable, net Electric Utilities $ 40,492 $ 33,907 $ (624 ) $ 73,775 Gas Utilities 120,910 60,142 (3,684 ) 177,368 Power Generation 1,580 — — 1,580 Mining 3,133 — — 3,133 Corporate 1,916 — — 1,916 Total $ 168,031 $ 94,049 $ (4,308 ) $ 257,772

Regulatory Accounting (Tables)

Regulatory Accounting (Tables)	3 Months Ended
	Mar. 31, 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: March 31, 2019 December 31, 2018 March 31, 2018 Regulatory assets Deferred energy and fuel cost adjustments (a) $ 35,512 $ 29,661 $ 25,056 Deferred gas cost adjustments (a) 5,124 3,362 2,118 Gas price derivatives (a) 3,939 6,201 11,045 Deferred taxes on AFUDC (b) 7,771 7,841 7,808 Employee benefit plans (c) 111,724 110,524 109,999 Environmental (a) 945 959 1,012 Loss on reacquired debt (a) 20,570 21,001 20,267 Renewable energy standard adjustment (a) 1,533 1,722 1,600 Deferred taxes on flow through accounting (c) 33,226 31,044 28,014 Decommissioning costs (b) 11,694 11,700 12,552 Gas supply contract termination (a) 12,866 14,310 18,590 Other regulatory assets (a) 41,803 45,910 29,171 Total regulatory assets 286,707 284,235 267,232 Less current regulatory assets (54,303 ) (48,776 ) (54,492 ) Regulatory assets, non-current $ 232,404 $ 235,459 $ 212,740 Regulatory liabilities Deferred energy and gas costs (a) $ 19,018 $ 6,991 $ 20,194 Employee benefit plan costs and related deferred taxes (c) 42,207 42,533 40,332 Cost of removal (a) 154,170 150,123 139,002 Excess deferred income taxes (c) 307,894 310,562 310,622 TCJA revenue reserve 16,549 18,032 15,239 Other regulatory liabilities (c) 17,421 12,553 12,472 Total regulatory liabilities 557,259 540,794 537,861 Less current regulatory liabilities (45,777 ) (29,810 ) (42,499 ) Regulatory liabilities, non-current $ 511,482 $ 510,984 $ 495,362 __________ (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)	3 Months Ended
	Mar. 31, 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: March 31, 2019 December 31, 2018 March 31, 2018 Materials and supplies $ 76,728 $ 75,081 $ 72,045 Fuel - Electric Utilities 2,485 2,850 2,903 Natural gas in storage held for distribution 8,463 39,368 7,097 Total materials, supplies and fuel $ 87,676 $ 117,299 $ 82,045

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2019 2018 Net income available for common stock $ 103,808 $ 133,004 Weighted average shares - basic 59,920 53,319 Dilutive effect of: Equity Units (a) — 733 Equity compensation 140 70 Weighted average shares - diluted 60,060 54,122 __________ (a) Calculated using the treasury stock method. On November 1, 2018, we completed settlement of the stock purchase contracts that are 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 March 31, 2019 2018 Equity compensation 6 71 Anti-dilutive shares 6 71

Notes Payable, Current Maturi_2

Notes Payable, Current Maturities and Debt (Tables)	3 Months Ended
	Mar. 31, 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: March 31, 2019 December 31, 2018 March 31, 2018 Balance Outstanding Letters of Credit Balance Outstanding Letters of Credit Balance Outstanding Letters of Credit Revolving Credit Facility $ — $ 14,006 $ — $ 22,310 $ — $ 15,830 CP Program 164,650 — 185,620 — 164,200 — Total $ 164,650 $ 14,006 $ 185,620 $ 22,310 $ 164,200 $ 15,830
Schedule of Credit Facility Covenants	Our Revolving Credit Facility and term loans require compliance with the following financial covenant at the end of each quarter: As of March 31, 2019 Covenant Requirement Consolidated Indebtedness to Capitalization Ratio 58.1% Less than 65%

Equity (Tables)

Equity (Tables)	3 Months Ended
	Mar. 31, 2019
Statement of Stockholders' Equity [Abstract]
Schedule of Stockholders Equity	A summary of the changes in equity is as follows: Three Months Ended March 31, 2019 Common Stock Treasury Stock (in thousands except share amounts) Shares Value Shares Value Additional Paid in Capital Retained Earnings AOCI Non controlling Interest Total December 31, 2018 60,048,567 $ 60,049 44,253 $ (2,510 ) $ 1,450,569 $ 700,396 $ (26,916 ) $ 105,835 $ 2,287,423 Net income (loss) available for common stock — — — — — 103,808 — 3,554 107,362 Other comprehensive income (loss), net of tax — — — — — — 457 — 457 Dividends on common stock ($0.505 per share) — — — — — (30,332 ) — — (30,332 ) Share-based compensation 48,956 49 (20,497 ) 1,078 (589 ) — — — 538 Issuance of common stock 280,497 280 — — 19,719 — — — 19,999 Issuance costs — — — — (289 ) — — — (289 ) Cumulative effect of ASU 2016-02, Leases implementation — — — — — 3,390 — — 3,390 Distributions to noncontrolling interest — — — — — — — (4,846 ) (4,846 ) March 31, 2019 60,378,020 $ 60,378 23,756 $ (1,432 ) $ 1,469,410 $ 777,262 $ (26,459 ) $ 104,543 $ 2,383,702 Three Months Ended March 31, 2018 Common Stock Treasury Stock (in thousands except share amounts) Shares Value Shares Value Additional Paid in Capital Retained Earnings AOCI Non controlling Interest Total December 31, 2017 53,579,986 $ 53,580 39,064 $ (2,306 ) $ 1,150,285 $ 548,617 $ (41,202 ) $ 111,232 $ 1,820,206 Net income (loss) available for common stock — — — — — 133,004 — 3,630 136,634 Other comprehensive income (loss), net of tax — — — — — — 1,260 — 1,260 Dividends on common stock ($0.475 per share) — — — — — (25,444 ) — — (25,444 ) Share-based compensation 64,770 65 14,895 (743 ) 1,433 — — — 755 Dividend reinvestment and stock purchase plan 4,061 4 — — 215 — — — 219 Other stock transactions — — — — — (16 ) 18 — 2 Distributions to noncontrolling interest — — — — — — — (5,648 ) (5,648 ) March 31, 2018 53,648,817 $ 53,649 53,959 $ (3,049 ) $ 1,151,933 $ 656,161 $ (39,924 ) $ 109,214 $ 1,927,984

Risk Management Activities (Tab

Risk Management Activities (Tables)	3 Months Ended
	Mar. 31, 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: March 31, 2019 December 31, 2018 March 31, 2018 Notional (MMBtus) Maximum Term (months) (a) Notional (MMBtus) Maximum Term (months) (a) Notional (MMBtus) Maximum Term (months) (a) Natural gas futures purchased 3,120,000 21 4,000,000 24 6,760,000 33 Natural gas options purchased, net 1,150,000 10 4,320,000 13 170,000 11 Natural gas basis swaps purchased 3,020,000 21 3,960,000 24 6,770,000 33 Natural gas over-the-counter swaps, net (b) 3,316,000 26 3,660,000 24 2,760,000 26 Natural gas physical contracts, net (c) 2,786,980 12 18,325,852 30 386,250 32 __________ (a) Term reflects the maximum forward period hedged. (b) As of March 31, 2019 , 534,000 MMBtus were designated as cash flow hedges. (c)
Derivative Instruments, Gain (Loss)	The impacts of cash flow hedges on our Condensed Consolidated Statements of Income is presented below for the three months ended March 31, 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 March 31, 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 554 Total $ (159 ) Three Months Ended March 31, 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 $ (713 ) Commodity derivatives Fuel, purchased power and cost of natural gas sold (621 ) Total $ (1,334 ) 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 months ended March 31, 2019 and 2018 . Three Months Ended March 31, 2019 2018 (in thousands) Increase (decrease) in fair value: Forward commodity contracts $ 234 $ (297 ) Recognition of (gains) losses in earnings due to settlements: Interest rate swaps 713 713 Forward commodity contracts (554 ) 621 Total other comprehensive income (loss) from hedging $ 393 $ 1,037 Derivatives Not Designated as Hedge Instruments The following table summarizes the impacts of derivative instruments not designated as hedge instruments on our Condensed Consolidated Statements of Income for the three months ended March 31, 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 March 31, 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 $ 25 $ 254 $ 25 $ 254 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 assets or Regulatory liability accounts related to the hedges in our utilities were $3.9 million , $6.2 million and $11 million at March 31, 2019 , December 31, 2018 and March 31, 2018

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Schedule of Fair Value Hierarchy, Measured on Recurring Basis	Recurring Fair Value Measurements As of March 31, 2019 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting Total (in thousands) Assets: Commodity derivatives — Utilities $ — $ 1,375 $ — $ (388 ) $ 987 Total $ — $ 1,375 $ — $ (388 ) $ 987 Liabilities: Commodity derivatives — Utilities $ — $ 4,122 $ — $ (4,009 ) $ 113 Total $ — $ 4,122 $ — $ (4,009 ) $ 113 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 As of March 31, 2018 Level 1 Level 2 Level 3 Cash Collateral and Counterparty Netting Total (in thousands) Assets: Commodity derivatives — Utilities $ — $ 414 $ — $ (119 ) $ 295 Total $ — $ 414 $ — $ (119 ) $ 295 Liabilities: Commodity derivatives — Utilities $ — $ 12,259 $ — $ (11,175 ) $ 1,084 Total $ — $ 12,259 $ — $ (11,175 ) $ 1,084
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 March 31, 2019 December 31, 2018 March 31, 2018 Derivatives designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets — current $ 131 $ 415 $ — Noncurrent commodity derivatives Other assets, non-current 9 18 — Liability derivative instruments: Current commodity derivatives Derivative liabilities — current (11 ) (114 ) (394 ) Noncurrent commodity derivatives Other deferred credits and other liabilities — (4 ) (29 ) Total derivatives designated as hedges $ 129 $ 315 $ (423 ) Derivatives not designated as hedges: Asset derivative instruments: Current commodity derivatives Derivative assets — current $ 801 $ 1,085 $ 295 Noncurrent commodity derivatives Other assets, non-current 46 1 — Liability derivative instruments: Current commodity derivatives Derivative liabilities — current (84 ) (833 ) (497 ) Noncurrent commodity derivatives Other deferred credits and other liabilities (18 ) (56 ) (164 ) Total derivatives not designated as hedges $ 745 $ 197 $ (366 )

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	The estimated fair values of our financial instruments, excluding derivatives which are presented in Note 11 , were as follows (in thousands) as of: March 31, 2019 December 31, 2018 March 31, 2018 Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value Cash and cash equivalents (a) $ 12,225 $ 12,225 $ 20,776 $ 20,776 $ 30,947 $ 30,947 Restricted cash (a) $ 3,494 $ 3,494 $ 3,369 $ 3,369 $ 2,958 $ 2,958 Notes payable (b) $ 164,650 $ 164,650 $ 185,620 $ 185,620 $ 164,200 $ 164,200 Long-term debt, including current maturities (c) (d) $ 2,956,042 $ 3,137,538 $ 2,956,578 $ 3,039,108 $ 3,114,530 $ 3,265,965 __________ (a) Carrying value approximates fair value due to either the short-term length of maturity or variable interest rates that approximate prevailing market rates, and therefore is classified in Level 1 in the fair value hierarchy. (b) Notes payable consist of commercial paper borrowings and borrowings on our Revolving Credit Facility. Carrying value approximates fair value due to the short-term length of maturity; since these borrowings are not traded on an exchange, they are classified in Level 2 in the fair value hierarchy. (c) 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. (d)

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 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, net of tax (in thousands): Location on the Condensed Consolidated Statements of Income Amount Reclassified from AOCI Three Months Ended March 31, 2019 March 31, 2018 Gains and (losses) on cash flow hedges: Interest rate swaps Interest expense $ (713 ) $ (713 ) Commodity contracts Fuel, purchased power and cost of natural gas sold 554 (621 ) (159 ) (1,334 ) Income tax Income tax benefit (expense) 35 297 Total reclassification adjustments related to cash flow hedges, net of tax $ (124 ) $ (1,037 ) Amortization of components of defined benefit plans: Prior service cost Operations and maintenance $ 19 $ 45 Actuarial gain (loss) Operations and maintenance (220 ) (622 ) (201 ) (577 ) Income tax Income tax benefit (expense) 48 126 Total reclassification adjustments related to defined benefit plans, net of tax $ (153 ) $ (451 ) Total reclassifications $ (277 ) $ (1,488 )
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 — 180 — 180 Amounts reclassified from AOCI 550 (426 ) 153 277 As of March 31, 2019 $ (16,757 ) $ 82 $ (9,784 ) $ (26,459 ) Interest Rate Swaps Commodity Derivatives Employee Benefit Plans Total Balance as of December 31, 2017 $ (19,581 ) $ (518 ) $ (21,103 ) $ (41,202 ) Other comprehensive income (loss) before reclassifications — (228 ) — (228 ) Amounts reclassified from AOCI 561 476 451 1,488 Reclassifications of certain tax effects from AOCI 15 — 3 18 As of March 31, 2018 $ (19,005 ) $ (270 ) $ (20,649 ) $ (39,924 )

Supplemental Disclosure of Ca_2

Supplemental Disclosure of Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2019
Supplemental Cash Flow Information [Abstract]
Supplemental Disclosure of Cash Flow Information	Three Months Ended March 31, 2019 March 31, 2018 (in thousands) Non-cash investing and financing activities — Property, plant and equipment acquired with accrued liabilities $ 56,571 $ 21,708 Cash (paid) refunded during the period — Interest (net of amounts capitalized) $ (30,672 ) $ (36,928 ) Income taxes $ 8 $ (14,336 )

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2019 2018 Service cost $ 1,346 $ 1,708 Interest cost 4,343 3,867 Expected return on plan assets (6,100 ) (6,185 ) Prior service cost 6 15 Net loss (gain) 941 2,158 Net periodic benefit cost $ 536 $ 1,563 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 March 31, 2019 2018 Service cost $ 454 $ 573 Interest cost 560 521 Expected return on plan assets (57 ) (57 ) Prior service cost (benefit) (99 ) (99 ) Net loss (gain) — 54 Net periodic benefit cost $ 858 $ 992 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans The components of net periodic benefit cost for the Supplemental Non-qualified Defined Benefit and Defined Contribution Plans were as follows (in thousands): Three Months Ended March 31, 2019 2018 Service cost (a) $ 1,285 $ 280 Interest cost 324 293 Net loss (gain) 134 250 Net periodic benefit cost $ 1,743 $ 823
Schedule of Defined Benefit Plans Contributions	Contributions made in 2019 and anticipated contributions for 2019 and 2020 are as follows (in thousands): Contributions Made Additional Contributions Contributions Three Months Ended March 31, 2019 Anticipated for 2019 Anticipated for 2020 Defined Benefit Pension Plan $ — $ 12,700 $ 12,700 Non-pension Defined Benefit Postretirement Healthcare Plans $ 1,109 $ 3,326 $ 4,271 Supplemental Non-qualified Defined Benefit and Defined Contribution Plans $ 366 $ 1,097 $ 1,562

Discontinued Operations (Tables

Discontinued Operations (Tables)	3 Months Ended
	Mar. 31, 2019
Discontinued Operations and Disposal Groups [Abstract]
Disposal Groups, Including Discontinued Operations, Balance Sheet Accounts	As of (in thousands) March 31, 2018 Other current assets $ 4,332 Deferred income tax assets, noncurrent, net 3,739 Property, plant and equipment, net 16,653 Other current liabilities (17,233 ) Other noncurrent liabilities (7,677 ) Net (liabilities) $ (186 )

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	3 Months Ended
	Mar. 31, 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: March 31, 2019 December 31, 2018 March 31, 2018 Accrued employee compensation, benefits and withholdings $ 48,078 $ 63,742 $ 46,262 Accrued property taxes 43,662 42,510 42,912 Customer deposits and prepayments 39,125 43,574 35,748 Accrued interest and contract adjustment payments 35,149 31,759 30,426 CIAC current portion 1,485 1,485 1,552 Other (none of which is individually significant) 28,573 32,431 37,140 Total accrued liabilities $ 196,072 $ 215,501 $ 194,040

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Lessee Disclosure [Abstract]
Lease, Cost	The components of lease expense were as follows (in thousands): Income Statement Location Three Months Ended March 31, 2019 Operating lease cost Operations and maintenance $ 311 Finance lease cost: Amortization of right-of-use asset Depreciation, depletion and amortization 17 Interest on lease liabilities Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) 3 Total lease cost $ 331
Lessee - Supplemental Balance Sheet Information	Supplemental balance sheet information related to leases was as follows (in thousands): Balance Sheet Location As of March 31, 2019 Assets: Operating lease assets Other assets, non-current $ 5,331 Finance lease assets Other assets, non-current 481 Total lease assets $ 5,812 Liabilities: Current: Operating leases Accrued liabilities $ 974 Finance leases Accrued liabilities 92 Noncurrent: Operating leases Other deferred credits and other liabilities 4,563 Finance leases Other deferred credits and other liabilities 391 Total lease liabilities $ 6,020
Lessee - Supplemental Cash Flow Information	Supplemental cash flow information related to leases was as follows (in thousands): Three Months Ended March 31, 2019 Cash paid included in the measurement of lease liabilities: Operating cash flows from operating leases $ 246 Operating cash flows from finance lease $ 3 Financing cash flows from finance lease $ 15 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ 2,328 Finance leases $ —
Lessee - Supplemental Weighted Average Schedule	As of March 31, 2019 Weighted average remaining lease term (years): Operating leases 8 years Finance leases 5 years Weighted average discount rate: Operating leases 4.23 % Finance leases 4.21 %
Lessee, Operating Lease, Liability, Maturity	As of March 31, 2019 , scheduled maturities of lease liabilities for future years were as follows (in thousands): Operating Leases Finance Leases Total 2019 (a) $ 952 $ 83 $ 1,035 2020 936 111 1,047 2021 820 111 931 2022 698 111 809 2023 699 110 809 Thereafter 2,653 9 2,662 Total lease payments (b) $ 6,758 $ 535 $ 7,293 Less imputed interest 1,221 52 1,273 Present value of lease liabilities $ 5,537 $ 483 $ 6,020 (a) Includes lease liabilities for the remaining nine 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
Lessee - Finance Lease, Liability, Maturity	As of March 31, 2019 , scheduled maturities of lease liabilities for future years were as follows (in thousands): Operating Leases Finance Leases Total 2019 (a) $ 952 $ 83 $ 1,035 2020 936 111 1,047 2021 820 111 931 2022 698 111 809 2023 699 110 809 Thereafter 2,653 9 2,662 Total lease payments (b) $ 6,758 $ 535 $ 7,293 Less imputed interest 1,221 52 1,273 Present value of lease liabilities $ 5,537 $ 483 $ 6,020 (a) Includes lease liabilities for the remaining nine months of 2019 . (b)
Lessor Disclosure [Abstract]
Operating Lease, Lease Income	The components of lease revenue were as follows (in thousands): Income Statement Location Three Months Ended March 31, 2019 Operating lease income Revenue $ 638
Lessor - Operating and Finance Lease, Liability, Maturity	As of March 31, 2019 , scheduled maturities of lease receivables for future years were as follows (in thousands): Operating Leases 2019 (a) $ 1,652 2020 2,010 2021 1,843 2022 1,793 2023 1,799 Thereafter 55,481 Total lease receivables $ 64,578 (a) Includes lease receivables for the remaining nine months of 2019

Management's Statement (Details

Management's Statement (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease - right of use assets	$ 5,331
Operating lease liabilities	5,537
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 3,390
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease - right of use assets		$ 3,100
Operating lease liabilities		3,200
Accrued Rent Receivable		4,500
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 3,400

Revenue_ Disaggregation of Reve

Revenue: Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 597,970	$ 573,355
Total revenues	597,810	575,389
Changes To Our Segment Performance Measure - Revenues	0
Recasting of Intercompany Capital Lease
Disaggregation of Revenue [Line Items]
Changes To Our Segment Performance Measure - Revenues		0
Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7,701	8,715
Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	590,269	564,640
Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(160)	2,034
Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	515,439	497,166
Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	44,085	41,260
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10,599	10,770
Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4,685	2,049
Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	23,162	22,110
Inter-company Revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(28,200)	(27,453)
Total revenues	(37,871)	(36,577)
Inter-company Revenues | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(8,128)	(7,842)
Inter-company Revenues | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(20,072)	(19,611)
Inter-company Revenues | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(9,671)	(9,124)
Inter-company Revenues | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(8,128)	(7,842)
Inter-company Revenues | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(432)	(409)
Inter-company Revenues | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(13,213)	(13,049)
Inter-company Revenues | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(2,224)	(2,522)
Inter-company Revenues | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(4,203)	(3,631)
Electric Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	182,673	173,322
Total revenues	182,927	173,555
Electric Utilities | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Electric Utilities | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	182,673	173,322
Electric Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	254	233
Electric Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	153,463	147,057
Electric Utilities | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Electric Utilities | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8,343	9,050
Electric Utilities | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,692	4,144
Electric Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,175	13,071
Gas Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	412,199	396,160
Total revenues	411,080	397,344
Gas Utilities | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Gas Utilities | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	412,199	396,160
Gas Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(1,119)	1,184
Gas Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	354,275	341,394
Gas Utilities | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	44,517	41,669
Gas Utilities | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Gas Utilities | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	217	427
Gas Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13,190	12,670
Power Generation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,469	14,769
Total revenues	25,245	23,939
Changes To Our Segment Performance Measure - Revenues	3,400
Power Generation | Recasting of Intercompany Capital Lease
Disaggregation of Revenue [Line Items]
Changes To Our Segment Performance Measure - Revenues		800
Power Generation | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Power Generation | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,469	14,769
Power Generation | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	9,776	9,170
Power Generation | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Power Generation | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Power Generation | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,469	14,769
Power Generation | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Power Generation | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Mining
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,829	16,557
Total revenues	16,429	17,128
Mining | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,829	16,557
Mining | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Mining | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	600	571
Mining | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,829	16,557
Mining | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Mining | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Mining | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Mining | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0

Business Segment Information_ I

Business Segment Information: Information Relating to Segment Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information
Revenue from contracts with customers	$ 597,970	$ 573,355
Revenues	597,810	575,389
Operating income	160,131	148,274
Interest expense, net	(34,717)	(34,995)
Other income (expense), net	(789)	(104)
Income tax benefit (expense)	(17,263)	25,802
Income from continuing operations	107,362	138,977
Net (loss) from discontinued operations	0	(2,343)
Net income	107,362	136,634
Net income attributable to noncontrolling interest	(3,554)	(3,630)
Net income available for common stock	103,808	133,004
Changes To Our Segment Performance Measure - Revenues	0
Changes To Our Segment Performance Measure - Operating Income	0
Deferred income taxes	19,602	(25,430)
Other 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
Changes To Our Segment Performance Measure - Operating Income		0
Inter-company Revenues
Segment Reporting Information
Revenue from contracts with customers	(28,200)	(27,453)
Revenues	(37,871)	(36,577)
Consolidation, Eliminations
Segment Reporting Information
Revenue from contracts with customers	0	0
Corporate
Segment Reporting Information
Operating income	(507)	(1,696)
Changes To Our Segment Performance Measure - Operating Income	4,700
Corporate | Recasting of Intercompany Capital Lease
Segment Reporting Information
Changes To Our Segment Performance Measure - Operating Income		(100)
Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	182,673	173,322
Revenues	182,927	173,555
Operating income	41,020	38,480
Electric Utilities | Recasting of Intercompany Capital Lease
Segment Reporting Information
Changes To Our Segment Performance Measure - Operating Income		1,700
Electric Utilities | Segment Reconciling Items [Member]
Segment Reporting Information
Changes To Our Segment Performance Measure - Operating Income	(5,400)
Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	412,199	396,160
Revenues	411,080	397,344
Operating income	103,314	95,443
Power Generation
Segment Reporting Information
Revenue from contracts with customers	15,469	14,769
Revenues	25,245	23,939
Operating income	11,967	11,776
Changes To Our Segment Performance Measure - Revenues	3,400
Power Generation | Recasting of Intercompany Capital Lease
Segment Reporting Information
Changes To Our Segment Performance Measure - Revenues		800
Changes To Our Segment Performance Measure - Operating Income		(1,600)
Power Generation | Segment Reconciling Items [Member]
Segment Reporting Information
Changes To Our Segment Performance Measure - Operating Income	700
Mining
Segment Reporting Information
Revenue from contracts with customers	15,829	16,557
Revenues	16,429	17,128
Operating income	4,337	4,271
Other Revenues
Segment Reporting Information
Revenues	(160)	2,034
Other Revenues | Inter-company Revenues
Segment Reporting Information
Revenues	(9,671)	(9,124)
Other Revenues | Consolidation, Eliminations
Segment Reporting Information
Revenues	0	0
Other Revenues | Electric Utilities
Segment Reporting Information
Revenues	254	233
Other Revenues | Gas Utilities
Segment Reporting Information
Revenues	(1,119)	1,184
Other Revenues | Power Generation
Segment Reporting Information
Revenues	9,776	9,170
Other Revenues | Mining
Segment Reporting Information
Revenues	600	571
External Operating Revenue
Segment Reporting Information
Revenue from contracts with customers	597,970	573,355
External Operating Revenue | Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	176,663	167,178
External Operating Revenue | Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	411,500	395,742
External Operating Revenue | Power Generation
Segment Reporting Information
Revenue from contracts with customers	2,257	1,720
External Operating Revenue | Mining
Segment Reporting Information
Revenue from contracts with customers	7,550	8,715
External Operating Revenue | Other Revenues
Segment Reporting Information
Revenues	(160)	2,034
External Operating Revenue | Other Revenues | Electric Utilities
Segment Reporting Information
Revenues	254	233
External Operating Revenue | Other Revenues | Gas Utilities
Segment Reporting Information
Revenues	(1,119)	1,184
External Operating Revenue | Other Revenues | Power Generation
Segment Reporting Information
Revenues	436	371
External Operating Revenue | Other Revenues | Mining
Segment Reporting Information
Revenues	269	246
Inter-company Operating Revenue | Electric Utilities
Segment Reporting Information
Revenue from contracts with customers	6,010	6,144
Inter-company Operating Revenue | Gas Utilities
Segment Reporting Information
Revenue from contracts with customers	699	418
Inter-company Operating Revenue | Power Generation
Segment Reporting Information
Revenue from contracts with customers	13,212	13,049
Inter-company Operating Revenue | Mining
Segment Reporting Information
Revenue from contracts with customers	8,279	7,842
Inter-company Operating Revenue | Other Revenues | Electric Utilities
Segment Reporting Information
Revenues	0	0
Inter-company Operating Revenue | Other Revenues | Gas Utilities
Segment Reporting Information
Revenues	0	0
Inter-company Operating Revenue | Other Revenues | Power Generation
Segment Reporting Information
Revenues	9,340	8,799
Inter-company Operating Revenue | Other Revenues | Mining
Segment Reporting Information
Revenues	$ 331	$ 325

Business Segment Information_ S

Business Segment Information: Segment and Corporate Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 7,037,572	$ 6,963,327	$ 6,626,989
Changes To Our Segment Performance Measure - Assets	0
Discontinued Operations, Held-for-sale
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	0	0	24,724
Corporate
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	207,495	209,478	194,193
Electric Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,755,056	2,707,695	2,629,267
Changes To Our Segment Performance Measure - Assets	(186,000)
Gas Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	3,639,430	3,623,475	3,398,473
Power Generation
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	372,503	342,085	314,764
Changes To Our Segment Performance Measure - Assets	186,000
Mining
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 63,088	80,594	65,568
Recasting of Intercompany Capital Lease
Segment Reporting, Asset Reconciling Item [Line Items]
Changes To Our Segment Performance Measure - Assets		0	0
Recasting of Intercompany Capital Lease | Electric Utilities
Segment Reporting, Asset Reconciling Item [Line Items]
Changes To Our Segment Performance Measure - Assets		(188,000)	(261,000)
Recasting of Intercompany Capital Lease | Power Generation
Segment Reporting, Asset Reconciling Item [Line Items]
Changes To Our Segment Performance Measure - Assets		$ 188,000	$ 261,000

Accounts Receivable (Details)

Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Accounts Receivable [Line Items]
Accounts Receivable, Trade	$ 193,673	$ 146,716	$ 168,031
Unbilled Receivables, Current	93,641	125,646	94,049
Allowance for Doubtful Accounts	(4,712)	(3,209)	(4,308)
Accounts receivable, net	282,602	269,153	257,772
Corporate
Accounts Receivable [Line Items]
Accounts Receivable, Trade	3,946	5,008	1,916
Unbilled Receivables, Current	0	0	0
Allowance for Doubtful Accounts	(169)	(169)	0
Accounts receivable, net	3,777	4,839	1,916
Electric Utilities
Accounts Receivable [Line Items]
Accounts Receivable, Trade	45,764	39,721	40,492
Unbilled Receivables, Current	31,075	35,125	33,907
Allowance for Doubtful Accounts	(535)	(448)	(624)
Accounts receivable, net	76,304	74,398	73,775
Gas Utilities
Accounts Receivable [Line Items]
Accounts Receivable, Trade	138,005	96,123	120,910
Unbilled Receivables, Current	62,566	90,521	60,142
Allowance for Doubtful Accounts	(4,008)	(2,592)	(3,684)
Accounts receivable, net	196,563	184,052	177,368
Power Generation
Accounts Receivable [Line Items]
Accounts Receivable, Trade	3,167	1,876	1,580
Unbilled Receivables, Current	0	0	0
Allowance for Doubtful Accounts	0	0	0
Accounts receivable, net	3,167	1,876	1,580
Mining
Accounts Receivable [Line Items]
Accounts Receivable, Trade	2,791	3,988	3,133
Unbilled Receivables, Current	0	0	0
Allowance for Doubtful Accounts	0	0	0
Accounts receivable, net	$ 2,791	$ 3,988	$ 3,133

Regulatory Accounting (Details)

Regulatory Accounting (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Regulatory assets
Regulatory assets	$ 286,707	$ 284,235	$ 267,232
Less current regulatory assets	(54,303)	(48,776)	(54,492)
Regulatory assets, non-current	232,404	235,459	212,740
Regulatory liabilities
Regulatory liabilities	557,259	540,794	537,861
Less current regulatory liabilities	(45,777)	(29,810)	(42,499)
Regulatory liabilities, non-current	511,482	510,984	495,362
Deferred energy and gas costs
Regulatory liabilities
Regulatory liabilities	19,018	6,991	20,194
Employee benefit plans
Regulatory liabilities
Regulatory liabilities	42,207	42,533	40,332
Cost of removal
Regulatory liabilities
Regulatory liabilities	154,170	150,123	139,002
Excess deferred income taxes
Regulatory liabilities
Regulatory liabilities	307,894	310,562	310,622
TCJA revenue reduction
Regulatory liabilities
Regulatory liabilities	16,549	18,032	15,239
Other regulatory liabilities
Regulatory liabilities
Regulatory liabilities	17,421	12,553	12,472
Deferred energy and gas costs
Regulatory assets
Regulatory assets	35,512	29,661	25,056
Deferred gas cost adjustments
Regulatory assets
Regulatory assets	5,124	3,362	2,118
Gas price derivatives
Regulatory assets
Regulatory assets	3,939	6,201	11,045
Deferred taxes on AFUDC
Regulatory assets
Regulatory assets	7,771	7,841	7,808
Employee benefit plans
Regulatory assets
Regulatory assets	111,724	110,524	109,999
Environmental
Regulatory assets
Regulatory assets	945	959	1,012
Loss on reacquired debt
Regulatory assets
Regulatory assets	20,570	21,001	20,267
Renewable energy standard adjustment
Regulatory assets
Regulatory assets	1,533	1,722	1,600
Deferred taxes on flow through accounting
Regulatory assets
Regulatory assets	33,226	31,044	28,014
Decommissioning costs
Regulatory assets
Regulatory assets	11,694	11,700	12,552
Gas supply contract termination
Regulatory assets
Regulatory assets	12,866	14,310	18,590
Other regulatory assets
Regulatory assets
Regulatory assets	$ 41,803	$ 45,910	$ 29,171

Regulatory Accounting_ Rate Rev

Regulatory Accounting: Rate Review (Details) $ in Millions	Feb. 01, 2019USD ($)	Mar. 29, 2019utility	Mar. 06, 2019utility
Application Filed | Nebraska Public Service Commission (NPSC) | Black Hills Energy, Nebraska Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Number of Companies Being Merged		2
Application Filed | Wyoming Public Service Commission (WPSC) | Black Hills Energy, Wyoming Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Number of Companies Being Merged			4
Rate Review Filed with the Regulatory Agency | Colorado Public Utilities Commission (CPUC) | Black Hills Energy, Colorado Gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase, Amount | $	$ 2.5

Materials, Supplies and Fuel (D

Materials, Supplies and Fuel (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Inventory, Net [Abstract]
Materials and supplies	$ 76,728	$ 75,081	$ 72,045
Fuel - Electric Utilities	2,485	2,850	2,903
Natural gas in storage held for distribution	8,463	39,368	7,097
Total materials, supplies and fuel	$ 87,676	$ 117,299	$ 82,045

Earnings Per Share_ Earnings Pe

Earnings Per Share: Earnings Per Share Reconciliation (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income available for common stock	$ 103,808	$ 133,004
Weighted average shares - basic (in shares)	59,920	53,319
Dilutive effect of:
Equity Units (in shares)	0	733
Equity compensation (in shares)	140	70
Weighted average shares - diluted (in shares)	60,060	54,122

Earnings Per Share_ Anti-diluti

Earnings Per Share: Anti-dilutive shares (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares	6	71
Equity compensation
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares	6	71

Notes Payable, Current Maturi_3

Notes Payable, Current Maturities and Debt: Schedule of Short-term Debt and Narrative (Details)	Jul. 30, 2018USD ($)credit_extension	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)
Short-term Debt [Line Items]
Notes payable		$ 164,650,000	$ 164,200,000	$ 185,620,000
Letters of Credit		14,006,000	15,830,000	22,310,000
Commercial paper, maximum borrowing capacity		750,000,000
Net (payments) borrowings of short-term debt		(20,970,000)	(47,100,000)
Commercial Paper
Short-term Debt [Line Items]
Notes payable		$ 164,650,000	164,200,000	185,620,000
Debt instrument, term		397 days
Net (payments) borrowings of short-term debt		$ (21,000,000)
Short-term interest rate		2.70%
Revolving Credit Facility
Short-term Debt [Line Items]
Notes payable		$ 0	0	0
Letters of Credit		$ 14,006,000	$ 15,830,000	$ 22,310,000
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)	Mar. 31, 2019
Maximum
Line of Credit Facility [Line Items]
Consolidated Indebtedness to Capitalization Ratio	0.65
Revolving Credit Facility
Line of Credit Facility [Line Items]
Recourse Leverage Ratio	58.10%
Debt instrument, covenant, Leverage Recourse Ratio	0.65

Equity_ Stockholders Equity Rec

Equity: Stockholders Equity Recap (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury Stock, Shares	23,756	53,959	44,253
Total Equity, beginning balance	$ 2,287,423	$ 1,820,206
Net income available for common stock	103,808	133,004
Net income attributable to noncontrolling interest	(3,554)	(3,630)
Net income	107,362	136,634
Other comprehensive income	457	1,260
Dividends on common stock	(30,332)	(25,444)
Share-based compensation	538	755
Stock Issued During Period, Value, New Issues	19,999
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	(289)
Cumulative Effect of New Accounting Principle in Period of Adoption	3,390
Dividend reinvestment and stock purchase plan		219
Other stock transactions		2
Distribution to noncontrolling interest	(4,846)	(5,648)
Total Equity, ending balance	$ 2,383,702	$ 1,927,984
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding	60,378,020	53,648,817	60,048,567	53,579,986
Total Equity, beginning balance	$ 60,049	$ 53,580
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures	48,956	64,770
Share-based compensation	$ 49	$ 65
Stock Issued During Period, Shares, New Issues	280,497
Stock Issued During Period, Value, New Issues	$ 280
Stock Issued During Period, Shares, Dividend Reinvestment Plan		4,061
Dividend reinvestment and stock purchase plan		$ 4
Total Equity, ending balance	$ 60,378	$ 53,649
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury Stock, Shares	23,756	53,959	44,253	39,064
Total Equity, beginning balance	$ (2,510)	$ (2,306)
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures	(20,497)	14,895
Share-based compensation	$ 1,078	$ (743)
Total Equity, ending balance	(1,432)	(3,049)
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total Equity, beginning balance	1,450,569	1,150,285
Share-based compensation	(589)	1,433
Stock Issued During Period, Value, New Issues	19,719
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	(289)
Dividend reinvestment and stock purchase plan		215
Total Equity, ending balance	1,469,410	1,151,933
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total Equity, beginning balance	700,396	548,617
Net income available for common stock	103,808	133,004
Dividends on common stock	(30,332)	(25,444)
Cumulative Effect of New Accounting Principle in Period of Adoption	3,390
Other stock transactions		(16)
Total Equity, ending balance	777,262	656,161
AOCI Attributable to Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total Equity, beginning balance	(26,916)	(41,202)
Other comprehensive income	457	1,260
Other stock transactions		18
Total Equity, ending balance	(26,459)	(39,924)
Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total Equity, beginning balance	105,835	111,232
Net income attributable to noncontrolling interest	3,554	3,630
Distribution to noncontrolling interest	(4,846)	(5,648)
Total Equity, ending balance	$ 104,543	$ 109,214

Equity_ At-the-Market Equity Of

Equity: At-the-Market Equity Offering Program (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Aug. 04, 2017
At The Market Equity Offering Program Authorized Aggregate Value		$ 300
Payments of Stock Issuance Costs	$ 0.2
Common Stock
At The Market Equity Offering Program Shares Issued	280,497
At The Market Equity Program Proceeds from Sale of Stock	$ 20

Equity_ Dividends on Common Sto

Equity: Dividends on Common Stock (Details) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Stockholders' Equity [Abstract]
Dividends per share of common stock (usd per share)	$ 0.505	$ 0.475

Risk Management Activities_ Uti

Risk Management Activities: Utilities (Details) - Natural Gas, Distribution $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019USD ($)MMBTU	Mar. 31, 2018MMBTU	Dec. 31, 2018MMBTU
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months | $	$ 0.1
Cash Flow Hedging
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure	534,000
Natural gas futures purchased
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	3,120,000	6,760,000	4,000,000
Derivative, Remaining Maturity	21 months	33 months	24 months
Natural gas options purchased, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	1,150,000	170,000	4,320,000
Derivative, Remaining Maturity	10 months	11 months	13 months
Natural gas basis swaps purchased
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	3,020,000	6,770,000	3,960,000
Derivative, Remaining Maturity	21 months	33 months	24 months
Natural gas over-the-counter swaps, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	3,316,000	2,760,000	3,660,000
Derivative, Remaining Maturity	26 months	26 months	24 months
Credit Risk Derivative Liabilities, at Fair Value | $	$ 0.2
Natural gas physical contracts, net
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	2,786,980	386,250	18,325,852
Derivative, Remaining Maturity	12 months	32 months	30 months

Risk Management Activities_ Cas

Risk Management Activities: Cash Flow Hedges (Details) - Cash Flow Hedging - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (159)	$ (1,334)
Designated as Hedging Instrument
Derivative [Line Items]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax	393	1,037
Interest rate swaps | Designated as Hedging Instrument
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	713	713
Commodity Contract | Designated as Hedging Instrument
Derivative [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	234	(297)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(554)	621
Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) | Interest rate swaps
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(713)	(713)
Cost of Sales | Commodity Contract
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ 554	$ (621)

Risk Management Activities_ Der

Risk Management Activities: Derivatives Not Designated as Hedge Instruments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Derivative [Line Items]
Regulatory assets	$ 286,707	$ 267,232	$ 284,235
Deferred Derivative Gain (Loss)
Derivative [Line Items]
Regulatory assets	3,900	11,000	$ 6,200
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	25	254
Not Designated as Hedging Instrument | Cost of Sales
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 25	$ 254

Fair Value Measurements_ Schedu

Fair Value Measurements: Schedule of Fair Values (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 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	$ (388)	$ (1,408)	$ (119)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(4,009)	(5,794)	(11,175)
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	(388)	(1,408)	(119)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(4,009)	(5,794)	(11,175)
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	987	1,519	295
Derivative Liabilities, Total	113	1,007	1,084
Estimate of Fair Value Measurement | Utilities Group
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	987	1,519	295
Derivative Liabilities, Fair Value Disclosure	113	1,007	1,084
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	0	0	0
Derivative Liabilities, Total	0	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	0
Derivative Liabilities, Fair Value Disclosure	0	0	0
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	1,375	2,927	414
Derivative Liabilities, Total	4,122	6,801	12,259
Fair Value, Inputs, Level 2 | Utilities Group
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Commodity Derivatives	1,375	2,927	414
Derivative Liabilities, Fair Value Disclosure	4,122	6,801	12,259
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Total	0	0	0
Derivative Liabilities, Total	0	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	0
Derivative Liabilities, Fair Value Disclosure	$ 0	$ 0	$ 0

Fair Value Measurements_ Balanc

Fair Value Measurements: Balance Sheet Location (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Designated as Hedging Instrument
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Asset, Fair Value, Net	$ 129	$ 315	$ (423)
Not Designated as Hedging Instrument
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Asset, Fair Value, Net	745	197	(366)
Commodity Contract | Designated as Hedging Instrument | Derivative assets — current
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	131	415	0
Commodity Contract | Designated as Hedging Instrument | Other assets, non-current
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	9	18	0
Commodity Contract | Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(11)	(114)	(394)
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	0	(4)	(29)
Commodity Contract | Not Designated as Hedging Instrument | Derivative assets — current
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	801	1,085	295
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	46	1	0
Commodity Contract | Not Designated as Hedging Instrument | Derivative liabilities — current
Derivatives, Carrying Amount and Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(84)	(833)	(497)
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	$ (18)	$ (56)	$ (164)

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 12,225	$ 20,776	$ 30,947
Restricted cash	3,494	3,369	2,958
Notes payable	164,650	185,620	164,200
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	12,225	20,776	30,947
Restricted cash	3,494	3,369	2,958
Notes payable	164,650	185,620	164,200
Long-term debt, including current maturities	2,956,042	2,956,578	3,114,530
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Fair Value	12,225	20,776	30,947
Restricted Cash Fair Value Disclosure	3,494	3,369	2,958
Notes payable, Fair Value	164,650	185,620	164,200
Long-term debt, including current maturities, Fair Value	$ 3,137,538	$ 3,039,108	$ 3,265,965

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss): Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ 35,974	$ 35,438
Fuel, purchased power and cost of natural gas sold	248,779	247,639
Operations and maintenance	123,913	116,096
Income before income taxes	124,625	113,175
Income tax benefit (expense)	(17,263)	25,802
Net income	107,362	136,634
Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net income	(277)	(1,488)
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 before income taxes	(159)	(1,334)
Income tax benefit (expense)	35	297
Net income	(124)	(1,037)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges | Reclassification Out Of Accumulated Other Comprehensive Income | Interest rate swaps
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense	(713)	(713)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges | Reclassification Out Of Accumulated Other Comprehensive Income | Commodity Contract
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Fuel, purchased power and cost of natural gas sold	554	(621)
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	19	45
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	(220)	(622)
Accumulated Defined Benefit Plans Adjustment | Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	(201)	(577)
Income tax benefit (expense)	48	126
Net income	$ (153)	$ (451)

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss): Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 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	(26,459)	(39,924)
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	(9,784)	(20,649)
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	153	451
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	180	(228)
Reclassification from AOCI, Current Period, Tax		18
AOCI 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	277	1,488
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	(16,757)	(19,005)
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	550	561
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	180	(228)
Reclassification from AOCI, Current Period, Tax		0
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	82	(270)
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	$ (426)	$ 476

Supplemental Disclosure of Ca_3

Supplemental Disclosure of Cash Flow Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Non-cash Investing and Financing Activities from Continuing Operations [Abstract]
Property, plant and equipment acquired with accrued liabilities	$ 56,571	$ 21,708
Supplemental Cash Flow Elements [Abstract]
Interest (net of amounts capitalized)	(30,672)	(36,928)
Income taxes	$ 8	$ (14,336)

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 1,346	$ 1,708
Interest cost	4,343	3,867
Expected return on plan assets	(6,100)	(6,185)
Prior service cost (benefit)	6	15
Net loss (gain)	941	2,158
Net periodic benefit cost	536	1,563
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	0
Estimated Future Employer Contributions in Current Fiscal Year	12,700
Estimated Future Employer Contributions in Next Fiscal Year	12,700
Defined Benefit Postretirement Healthcare Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	454	573
Interest cost	560	521
Expected return on plan assets	(57)	(57)
Prior service cost (benefit)	(99)	(99)
Net loss (gain)	0	54
Net periodic benefit cost	858	992
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	1,109
Estimated Future Employer Contributions in Current Fiscal Year	3,326
Estimated Future Employer Contributions in Next Fiscal Year	4,271
Supplemental Non-qualified Defined Benefit and Defined Contribution Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	1,285	280
Interest cost	324	293
Net loss (gain)	134	250
Net periodic benefit cost	1,743	$ 823
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	366
Estimated Future Employer Contributions in Current Fiscal Year	1,097
Estimated Future Employer Contributions in Next Fiscal Year	$ 1,562

Commitments and Contingencies_

Commitments and Contingencies: Dividend Restrictions (Details) $ in Millions	Mar. 31, 2019USD ($)
Utilities Group
Related Party Transaction [Line Items]
Restricted Net Assets for Subsidiaries	$ 257

Discontinued Operations (Detail

Discontinued Operations (Details) $ in Thousands	Mar. 31, 2018USD ($)
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Other current assets	$ 4,332
Deferred income tax assets, noncurrent, net	3,739
Property, plant and equipment, net	16,653
Other current liabilities	(17,233)
Other noncurrent liabilities	(7,677)
Net (liabilities)	$ (186)

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Tax Expense (Benefit)	$ 17,263	$ (25,802)
Income tax expense (benefit) associated with changes in the prior estimated impact of tax reform on deferred income taxes	(1,800)	$ 2,300
Increase in income tax benefit from forecasted federal production tax credits and state investment tax credits	$ 3,400

Income Taxes_ Tax Benefit Relat

Income Taxes: Tax Benefit Related to Legal Restructuring (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Deferred Tax Assets, Goodwill and Intangible Assets		$ 49,000
Deferred income taxes	$ 19,602	(25,430)
Other Restructuring
Deferred income taxes		$ 49,000

Income Taxes_ TCJA (Details)

Income Taxes: TCJA (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income tax benefit for deferred tax amortization related to tax reform	$ (1.8)	$ 2.3

Accrued Liabilities (Details)

Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Payables and Accruals [Abstract]
Accrued employee compensation, benefits and withholdings	$ 48,078	$ 63,742	$ 46,262
Accrued property taxes	43,662	42,510	42,912
Customer deposits and prepayments	39,125	43,574	35,748
Accrued interest and contract adjustment payments	35,149	31,759	30,426
CIAC current portion	1,485	1,485	1,552
Other (none of which is individually significant)	28,573	32,431	37,140
Total accrued liabilities	$ 196,072	$ 215,501	$ 194,040

Leases_ Lessee (Details)

Leases: Lessee (Details)	3 Months Ended
	Mar. 31, 2019
Minimum
Lessee, Lease, Description [Line Items]
Lessee - Lease Term	1 year
Maximum
Lessee, Lease, Description [Line Items]
Lessee - Lease Term	37 years

Leases_ Lessee - Lease Costs (D

Leases: Lessee - Lease Costs (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Operating lease cost	$ 311
Amortization of right-of-use asset	17
Interest on lease liabilities	3
Total lease cost	$ 331

Leases_ Lessee - Supplemental B

Leases: Lessee - Supplemental Balance Sheet Information (Details) $ in Thousands	Mar. 31, 2019USD ($)
Leases [Abstract]
Operating lease assets	$ 5,331
Finance lease assets	481
Total lease assets	5,812
Operating lease liability, current	974
Finance lease liability, current	92
Operating lease liability, non-current	4,563
Finance lease liability, non-current	391
Total lease liabilities	$ 6,020

Leases_ Lessee - Supplemental C

Leases: Lessee - Supplemental Cash Flow Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Operating cash flows from operating leases	$ 246
Operating cash flows from finance lease	3
Financing cash flows from finance lease	15
Operating leases	2,328
Finance leases	$ 0

Leases_ Lessee - Weighted Avera

Leases: Lessee - Weighted Average Information (Details)	Mar. 31, 2019
Leases [Abstract]
Operating leases	8 years
Finance leases	5 years
Operating leases	4.23%
Finance leases	4.21%

Leases_ Lessee - Future Minimum

Leases: Lessee - Future Minimum Payments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Operating Leases
2019	$ 952
2020	936
2021	820
2022	698
2023	699
Thereafter	2,653
Total lease payments	6,758
Less imputed interest	1,221
Present Value of Lease Liabilities - Operating leases	5,537
Finance Leases
2019	83
2020	111
2021	111
2022	111
2023	110
Thereafter	9
Total lease payments	535
Less imputed interest	52
Present value of lease liabilities - Finance Leases	483
Operating and Finance Lease Total
2019	1,035
2020	1,047
2021	931
2022	809
2023	809
Thereafter	2,662
Total lease payments	7,293
Less imputed interest	1,273
Present value of lease liabilities	$ 6,020
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

Leases_ Lessor (Details)

Leases: Lessor (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Lessor, Lease, Description [Line Items]
Operating lease income	$ 638
Minimum
Lessor, Lease, Description [Line Items]
Lessor - Lease Term	1 year
Maximum
Lessor, Lease, Description [Line Items]
Lessor - Lease Term	35 years

Leases_ Lessor - Future Minimum

Leases: Lessor - Future Minimum Payments (Details) $ in Thousands	Mar. 31, 2019USD ($)
Operating Leases
2019	$ 1,652
2020	2,010
2021	1,843
2022	1,793
2023	1,799
Thereafter	55,481
Total lease receivables	$ 64,578