MDU Resources (MDU) 10-Q 6 May 21 2021 Q1 Quarterly report Financial data

Cover page

Cover page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 29, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	1-03480
Entity Registrant Name	MDU RESOURCES GROUP INC
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	30-1133956
Entity Address, Address Line One	1200 West Century Avenue
Entity Address, Address Line Two	P.O. Box 5650
Entity Address, City or Town	Bismarck
Entity Address, State or Province	ND
Entity Address, Postal Zip Code	58506-5650
City Area Code	701
Local Phone Number	530-1000
Title of 12(b) Security	Common Stock, par value $1.00 per share
Trading Symbol	MDU
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity common stock, shares outstanding		201,194,537
Entity Central Index Key	0000067716
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating revenues:
Operating revenues:	$ 1,227,938	$ 1,197,373
Operating expenses:
Operation and maintenance:	811,659	821,000
Purchased natural gas sold	176,237	165,412
Depreciation, depletion and amortization	73,723	69,239
Taxes, other than income	62,534	64,112
Electric fuel and purchased power	18,621	20,540
Total operating expenses	1,142,774	1,140,303
Operating income	85,164	57,070
Other income (expense)	3,354	(1,005)
Interest expense	23,453	24,553
Income before income taxes	65,065	31,512
Income taxes	12,949	5,973
Income from continuing operations	52,116	25,539
Income (loss) from discontinued operations, net of tax	15	(409)
Net income	$ 52,131	$ 25,130
Earnings per share - basic:
Income from continuing operations	$ 0.26	$ 0.13
Discontinued operations, net of tax	0	0
Earnings per share - basic	0.26	0.13
Earnings per share - diluted:
Income from continuing operations	0.26	0.13
Discontinued operations, net of tax	0	0
Earnings per share - diluted	$ 0.26	$ 0.13
Weighted average common shares outstanding - basic	200,708	200,440
Weighted average common shares outstanding - diluted	200,952	200,456
Regulated operation
Operating revenues:
Operating revenues:	$ 442,381	$ 418,682
Operating expenses:
Operation and maintenance:	94,333	87,608
Income from continuing operations	56,121	51,129
Nonregulated operation
Operating revenues:
Operating revenues:	785,557	778,691
Operating expenses:
Operation and maintenance:	717,326	733,392
Income from continuing operations	$ (4,005)	$ (25,590)

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net income	$ 52,131	$ 25,130
Other comprehensive income:
Reclassification adjustment for loss on derivative instruments included in net income, tax	37	36
Reclassification adjustment for loss on derivative instruments included in net income, net of tax	111	111
Postretirement liability adjustment:
Amortization of postretirement liability losses included in net periodic benefit cost, tax	151	149
Amortization of postretirement liability losses included in net periodic benefit cost, net of tax	466	462
Net unrealized gain (loss) on available-for-sale investments:
Net unrealized gain (loss) on available-for-sale investments arising during the period, tax	(12)	36
Net unrealized gain (loss) on available-for-sale investments arising during the period, net of tax	(44)	135
Reclassification adjustment for (gain) loss on available-for-sale investments included in net income, tax	9	0
Reclassification adjustment for (gain) loss on available-for-sale investments included in net income, net of tax	35	(1)
Net unrealized gain (loss) on available-for-sale investments	(9)	134
Other comprehensive income	568	707
Comprehensive income attributable to common stockholders	$ 52,699	$ 25,837

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Current assets:
Cash and cash equivalents	$ 55,094	$ 59,547	$ 116,526
Receivables, net	784,582	873,986	835,468
Inventories	316,737	291,167	305,958
Current regulatory assets	98,452	68,527	55,206
Prepayments and other current assets	68,409	44,120	60,230
Total current assets	1,323,274	1,337,347	1,373,388
Noncurrent assets:
Property, plant and equipment	8,288,879	8,300,770	8,008,338
Less accumulated depreciation, depletion and amortization	3,096,371	3,133,831	3,039,812
Net property, plant and equipment	5,192,508	5,166,939	4,968,526
Goodwill	714,963	714,963	713,527
Other intangible assets, net	23,961	25,496	34,250
Regulatory assets	379,917	379,381	348,189
Investments	167,741	165,022	145,237
Operating lease right-of-use assets	116,663	120,113	114,382
Other	150,248	144,111	153,017
Total noncurrent assets	6,746,001	6,716,025	6,477,128
Total assets	8,069,275	8,053,372	7,850,516
Current liabilities:
Short-term borrowings	50,000	50,000	0
Long-term debt due within one year	1,552	1,555	16,560
Accounts payable	379,348	426,264	384,339
Taxes payable	88,711	88,844	58,743
Dividends payable	42,740	42,611	41,608
Accrued compensation	69,612	90,629	55,199
Regulatory liabilities due within one year	34,266	31,450	60,072
Operating lease liabilities due within one year	32,562	33,655	31,141
Other accrued liabilities	201,246	198,514	176,817
Total current liabilities	900,037	963,522	824,479
Noncurrent liabilities:
Long-term debt	2,251,722	2,211,575	2,438,675
Deferred income taxes	528,551	516,098	515,711
Regulatory liabilities	429,060	428,075	443,205
Asset retirement obligations	445,170	440,356	417,469
Operating lease liabilities	84,494	86,868	83,414
Other	329,935	327,773	290,971
Total noncurrent liabilities	4,068,932	4,010,745	4,189,445
Commitments and contingencies
Stockholders' equity:
Common stock	201,733	201,061	201,061
Other paid-in capital	1,382,158	1,371,385	1,360,564
Retained earnings	1,567,551	1,558,363	1,319,988
Accumulated other comprehensive loss	(47,510)	(48,078)	(41,395)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)	(3,626)
Total stockholders' equity	3,100,306	3,079,105	2,836,592
Total liabilities and stockholders' equity	$ 8,069,275	$ 8,053,372	$ 7,850,516
Common Stock, Shares Authorized	500,000,000	500,000,000	500,000,000
Common Stock, Par or Stated Value Per Share	$ 1	$ 1	$ 1
Common Stock, Shares, Issued	201,733,458	201,061,198	201,061,198
Treasury Stock, Common, Shares	538,921	538,921	538,921

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Common stock	Other paid-in capital	Retained earnings	Accumulated other comprehensive loss	Treasury stock
Common stock balance (in shares) at Dec. 31, 2019		200,922,790
Treasury stock (in shares) at Dec. 31, 2019						(538,921)
Balance at Dec. 31, 2019	$ 2,847,246	$ 200,923	$ 1,355,404	$ 1,336,647	$ (42,102)	$ (3,626)
Net income	25,130			25,130
Other comprehensive income	707				707
Dividends declared on common stock	(41,789)			(41,789)
Stock-based compensation	2,250		2,250
Issuance of common stock upon vesting of stock-based compensation, tax withholding shares		26,406
Issuance of common stock upon vesting of stock-based compensation, tax withholding shares value		$ 26
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings			(388)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(362)
Issuance of common stock (shares)		112,002
Issuance of common stock	$ 3,410	$ 112	3,298
Common stock balance (in shares) at Mar. 31, 2020	201,061,198	201,061,198
Treasury stock (in shares) at Mar. 31, 2020						(538,921)
Balance at Mar. 31, 2020	$ 2,836,592	$ 201,061	1,360,564	1,319,988	(41,395)	$ (3,626)
Common stock balance (in shares) at Dec. 31, 2020	201,061,198	201,061,198
Treasury stock (in shares) at Dec. 31, 2020						(538,921)
Balance at Dec. 31, 2020	$ 3,079,105	$ 201,061	1,371,385	1,558,363	(48,078)	$ (3,626)
Net income	52,131			52,131
Other comprehensive income	568				568
Dividends declared on common stock	(42,943)			(42,943)
Stock-based compensation	2,574		2,574
Treasury Stock, Shares, Acquired						(392,294)
Treasury Stock, Value, Acquired, Cost Method	(6,701)					$ (6,701)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings			(10,828)
Treasury Stock, Shares, Retired						392,294
Treasury Stock, Retired, Cost Method, Amount						$ 6,701
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(4,127)
Issuance of common stock (shares)		672,260
Issuance of common stock	$ 19,699	$ 672	19,027
Common stock balance (in shares) at Mar. 31, 2021	201,733,458	201,733,458
Treasury stock (in shares) at Mar. 31, 2021						(538,921)
Balance at Mar. 31, 2021	$ 3,100,306	$ 201,733	$ 1,382,158	$ 1,567,551	$ (47,510)	$ (3,626)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities:
Net income	$ 52,131	$ 25,130
Income (loss) from discontinued operations, net of tax	15	(409)
Income from continuing operations	52,116	25,539
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	73,723	69,239
Deferred income taxes	9,843	1,813
Changes in current assets and liabilities, net of acquisitions:
Receivables	89,407	44,549
Inventories	(25,613)	(29,337)
Other current assets	(46,837)	14,959
Accounts payable	(41,965)	(24,105)
Other current liabilities	(13,977)	(23,259)
Other noncurrent changes	(1,052)	326
Net cash provided by continuing operations	95,645	79,724
Net cash used in discontinued operations	(25)	(434)
Net cash provided by operating activities	95,620	79,290
Investing activities:
Capital expenditures	(111,091)	(139,485)
Acquisitions, net of cash acquired	(1,023)	(67,593)
Net proceeds from sale or disposition of property and other	9,035	4,540
Investments	(3,248)	68
Net cash used in investing activities	(106,327)	(202,470)
Financing activities:
Issuance of short-term borrowings	50,000	0
Repayment of short-term borrowings	(50,000)	0
Issuance of long-term debt	93,295	248,021
Repayment of long-term debt	(53,301)	(36,242)
Proceeds from issuance of common stock	19,699	3,410
Dividends paid	(42,611)	(41,580)
Repurchase of common stock	(6,701)	0
Tax withholding on stock-based compensation	(4,127)	(362)
Net cash provided by financing activities	6,254	173,247
Increase (decrease) in cash and cash equivalents	(4,453)	50,067
Cash and cash equivalents -- beginning of year	59,547	66,459
Cash and cash equivalents -- end of period	$ 55,094	$ 116,526

Basis of presentation

Basis of presentation	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of presentation	Basis of presentation The accompanying consolidated interim financial statements were prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Interim financial statements do not include all disclosures provided in annual financial statements and, accordingly, these financial statements should be read in conjunction with those appearing in the 2020 Annual Report. The information is unaudited but includes all adjustments that are, in the opinion of management, necessary for a fair presentation of the accompanying consolidated interim financial statements and are of a normal recurring nature. Depreciation, depletion and amortization expense is reported separately on the Consolidated Statements of Income and therefore is excluded from the other line items within operating expenses. Beginning in March 2020, governmental restrictions and guidelines implemented to control the spread of COVID-19 reduced commercial and interpersonal activity throughout the Company's areas of operation. Most of the Company's products and services are considered essential and accordingly operations have generally been allowed to continue. The Company has experienced some inefficiency impacts as a result of the COVID-19 pandemic, including operation suspensions and interruptions at some locations to carry out preventive measures or in response to instances of positive tests or quarantines. The Company has assessed the impacts of the COVID-19 pandemic on its results of operations for the three months ended March 31, 2021 and 2020, and determined there were no material adverse impacts. The assets and liabilities of the Company's discontinued operations have been classified as held for sale and are included in prepayments and other current assets, noncurrent assets - other and other accrued liabilities on the Consolidated Balance Sheets. The results and supporting activities are shown in income (loss) from discontinued operations on the Consolidated Statements of Income. Unless otherwise indicated, the amounts presented in the accompanying notes to the consolidated financial statements relate to the Company's continuing operations.

New accounting standards

New accounting standards	3 Months Ended
	Mar. 31, 2021
Accounting Standards Update and Change in Accounting Principle [Abstract]
New accounting standards	New accounting standards Recently adopted accounting standards ASU 2018-14 - Changes to the Disclosure Requirements for Defined Benefit Plans In August 2018, the FASB issued guidance on modifying the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans as part of the disclosure framework project. The guidance removes disclosures that are no longer considered cost beneficial, clarifies the specific requirements of disclosures and adds disclosure requirements identified as relevant. The guidance adds, among other things, the requirement to include an explanation for significant gains and losses related to changes in benefit obligations for the period. The guidance removes, among other things, the disclosure requirement to disclose the amount of net periodic benefit costs to be amortized over the next fiscal year from accumulated other comprehensive income (loss) and the effects a one percentage point change in assumed health care cost trend rates will have on certain benefit components. The Company adopted the guidance on January 1, 2021, on a retrospective basis. The Company determined the new guidance will not materially impact its consolidated financial statement disclosures. ASU 2019-12 - Simplifying the Accounting for Income Taxes In December 2019, the FASB issued guidance on simplifying the accounting for income taxes by removing certain exceptions in ASC 740 and providing simplification amendments. The guidance removes exceptions on intraperiod tax allocations and reporting and provides simplification on accounting for franchise taxes, tax basis goodwill and tax law changes. The Company adopted the guidance on January 1, 2021, and determined it did not have a material impact on its results of operations, financial position, cash flows or disclosures. Recently issued accounting standards not yet adopted ASU 2020-04 - Reference Rate Reform In March 2020, the FASB issued optional guidance to ease the facilitation of the effects of reference rate reform on financial reporting. The guidance applies to certain contract modifications, hedging relationships and other transactions that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. LIBOR is expected to be retired with a full phase-out by the end of 2021 and replaced by a new reference rate, which includes SOFR. The guidance can be applied beginning in the interim period that includes March 12, 2020, and cannot be applied to contract modifications or hedging relationships entered into or evaluated after December 31, 2022. The Company has updated its credit agreements to include language regarding the successor or alternate rate to LIBOR, and a review of other contracts and agreements is on-going. The Company does not expect the guidance to have a material impact on its results of operations, financial position, cash flows or disclosures.

Seasonality of operations

Seasonality of operations	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Seasonality of operations	Seasonality of operations Some of the Company's operations are highly seasonal and revenues from, and certain expenses for, such operations may fluctuate significantly among quarterly periods. Accordingly, the interim results for particular businesses, and for the Company as a whole, may not be indicative of results for the full fiscal year.

Receivables and allowance for e

Receivables and allowance for expected credit losses	3 Months Ended
	Mar. 31, 2021
Credit Loss [Abstract]
Receivables and allowance for expected credit loss	Receivables and allowance for expected credit losses Receivables consists primarily of trade receivables from the sale of goods and services, which are recorded at the invoiced amount, and contract assets, net of expected credit losses. For more information on contract assets, see Note 9. The Company's trade receivables are all due in 12 months or less. The total balance of receivables past due 90 days or more was $33.9 million, $51.8 million and $43.9 million at March 31, 2021 and 2020, and December 31, 2020, respectively. The Company's expected credit losses are determined through a review using historical credit loss experience, changes in asset specific characteristics, current conditions and reasonable and supportable future forecasts, among other specific account data, and is performed at least quarterly. The Company develops and documents its methodology to determine its allowance for expected credit losses at each of its reportable business segments. Risk characteristics used by the business segments may include customer mix, knowledge of customers, general economic conditions of the various local economies and impacts of COVID-19, among others. Specific account balances are written off when management determines the amounts to be uncollectible. Management has reviewed the balance reserved through the allowance for expected credit losses and believes it is reasonable. Details of the Company's expected credit losses were as follows: Electric Natural gas Pipeline Construction Construction Total (In thousands) At December 31, 2020 $ 899 $ 2,571 $ 2 $ 6,164 $ 5,722 $ 15,358 Current expected credit loss provision 538 1,273 — (1,049) (1,079) (317) Less write-offs charged against the allowance 888 1,107 — 273 401 2,669 Credit loss recoveries collected 129 213 — — — 342 At March 31, 2021 $ 678 $ 2,950 $ 2 $ 4,842 $ 4,242 $ 12,714 Electric Natural gas Pipeline Construction Construction Total (In thousands) At January 1, 2020 $ 328 $ 1,056 $ — $ 5,357 $ 1,756 $ 8,497 Current expected credit loss provision 555 1,156 — 694 1,150 3,555 Less write-offs charged against the allowance 500 624 — 68 73 1,265 Credit loss recoveries collected 109 229 — — — 338 At March 31, 2020 $ 492 $ 1,817 $ — $ 5,983 $ 2,833 $ 11,125

Inventories and natural gas in

Inventories and natural gas in storage	3 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Inventories and natural gas in storage	Inventories and natural gas in storage Natural gas in storage for the Company's regulated operations is generally valued at lower of cost or market using the last-in, first-out method or lower of cost or net realizable value using the average cost or first-in, first-out method. The majority of all other inventories are valued at the lower of cost or net realizable value using the average cost method. The portion of the cost of natural gas in storage expected to be used within 12 months was included in inventories. Inventories on the Consolidated Balance Sheets were as follows: March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Aggregates held for resale $ 180,450 $ 155,976 $ 175,782 Asphalt oil 59,853 73,842 28,238 Materials and supplies 26,481 26,293 25,142 Merchandise for resale 24,319 23,109 21,087 Natural gas in storage (current) 8,113 7,872 21,919 Other 17,521 18,866 18,999 Total $ 316,737 $ 305,958 $ 291,167 The remainder of natural gas in storage, which largely represents the cost of gas required to maintain pressure levels for normal operating purposes, was included in noncurrent assets - other and was $47.5 million at March 31, 2021 and December 31, 2020, and $48.3 million at March 31, 2020.

Earnings per share

Earnings per share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Earnings per share	Earnings per share Basic earnings per share is computed by dividing net income by the weighted average number of shares of common stock outstanding during the applicable period. Diluted earnings per share is computed by dividing net income by the total of the weighted average number of shares of common stock outstanding during the applicable period, plus the effect of non-vested performance share awards and restricted stock units. Common stock outstanding includes issued shares less shares held in treasury. Net income was the same for both the basic and diluted earnings per share calculations. A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings per share calculations follows: Three Months Ended March 31, 2021 2020 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 200,708 200,440 Effect of dilutive performance share awards and restricted stock units 244 16 Weighted average common shares outstanding - diluted 200,952 200,456 Shares excluded from the calculation of diluted earnings per share — 68 Dividends declared per common share $ .2125 $ .2075

Equity

Equity	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Equity	Equity The Company currently has a shelf registration statement on file with the SEC, under which the Company may issue and sell any combination of common stock and debt securities. The Company may sell such securities if warranted by market conditions and the Company's capital requirements. In August 2020, the Company amended the Distribution Agreement dated February 22, 2019, with JP Morgan Securities LLC and MUFG Securities Americas Inc., as sales agents. This agreement allows the offering, issuance and sale of up to 6.4 million shares of the Company's common stock in connection with an "at-the-market" offering. The common stock may be offered for sale, from time to time, in accordance with the terms and conditions of this agreement. The Company issued 672,260 shares of common stock during the first quarter of 2021 pursuant to the "at-the-market" offering, receiving net proceeds of $19.7 million, which were used for capital expenditures. The Company incurred issuance costs of approximately $300,000 in connection with the sales of common stock under the "at-the-market" offering during the first quarter of 2021. The Company did not issue shares of common stock under the "at-the-market" offering during the first quarter of 2020. As of March 31, 2021, the Company had capacity to issue up to 5.7 million additional shares of common stock under the "at-the-market" offering program.

Accumulated other comprehensive

Accumulated other comprehensive income (loss)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Accumulated other comprehensive income (loss)	Accumulated other comprehensive income (loss) The after-tax changes in the components of accumulated other comprehensive loss were as follows: Net Unrealized Postretirement Net Unrealized Total (In thousands) At December 31, 2020 $ (984) $ (47,207) $ 113 $ (48,078) Other comprehensive loss before reclassifications — — (44) (44) Amounts reclassified from accumulated other comprehensive loss 111 466 35 612 Net current-period other comprehensive income (loss) 111 466 (9) 568 At March 31, 2021 $ (873) $ (46,741) $ 104 $ (47,510) Net Unrealized Postretirement Net Unrealized Total (In thousands) At December 31, 2019 $ (1,430) $ (40,734) $ 62 $ (42,102) Other comprehensive income before reclassifications — — 135 135 Amounts reclassified (to) from accumulated other comprehensive loss 111 462 (1) 572 Net current-period other comprehensive income 111 462 134 707 At March 31, 2020 $ (1,319) $ (40,272) $ 196 $ (41,395) The following amounts were reclassified out of accumulated other comprehensive loss into net income. The amounts presented in parenthesis indicate a decrease to net income on the Consolidated Statements of Income. The reclassifications were as follows: Three Months Ended Location on Consolidated March 31, 2021 2020 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ (148) $ (147) Interest expense 37 36 Income taxes (111) (111) Amortization of postretirement liability losses included in net periodic benefit cost (617) (611) Other income 151 149 Income taxes (466) (462) Reclassification adjustment on available-for-sale investments included in net income (44) 1 Other income 9 — Income taxes (35) 1 Total reclassifications $ (612) $ (572)

Revenue from contracts with cus

Revenue from contracts with customers	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Revenue from contracts with customers	Revenue from contracts with customers Revenue is recognized when a performance obligation is satisfied by transferring control over a product or service to a customer. Revenue is measured based on consideration specified in a contract with a customer and excludes any sales incentives and amounts collected on behalf of third parties. The Company is considered an agent for certain taxes collected from customers. As such, the Company presents revenues net of these taxes at the time of sale to be remitted to governmental authorities, including sales and use taxes. Disaggregation In the following tables, revenue is disaggregated by the type of customer or service provided. The Company believes this level of disaggregation best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The table also includes a reconciliation of the disaggregated revenue by reportable segments. For more information on the Company's business segments, see Note 17. Three Months Ended March 31, 2021 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 33,436 $ 203,137 $ — $ — $ — $ — $ 236,573 Commercial utility sales 32,928 120,052 — — — — 152,980 Industrial utility sales 10,029 8,812 — — — — 18,841 Other utility sales 1,566 — — — — — 1,566 Natural gas transportation — 12,452 29,417 — — — 41,869 Natural gas storage — — 4,029 — — — 4,029 Contracting services — — — 96,025 — — 96,025 Construction materials — — — 216,412 — — 216,412 Intrasegment eliminations — — — (46,716) — — (46,716) Inside specialty contracting — — — — 355,190 — 355,190 Outside specialty contracting — — — — 151,363 — 151,363 Other 9,773 3,009 2,660 — 36 3,341 18,819 Intersegment eliminations (136) (142) (26,229) (62) (1,042) (3,324) (30,935) Revenues from contracts with customers 87,596 347,320 9,877 265,659 505,547 17 1,216,016 Revenues out of scope (2,923) 2,886 36 — 11,923 — 11,922 Total external operating revenues $ 84,673 $ 350,206 $ 9,913 $ 265,659 $ 517,470 $ 17 $ 1,227,938 Three Months Ended March 31, 2020 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 32,349 $ 186,701 $ — $ — $ — $ — $ 219,050 Commercial utility sales 33,587 114,996 — — — — 148,583 Industrial utility sales 10,367 8,521 — — — — 18,888 Other utility sales 1,648 — — — — — 1,648 Natural gas transportation — 11,798 27,432 — — — 39,230 Natural gas gathering — — 2,090 — — — 2,090 Natural gas storage — — 3,046 — — — 3,046 Contracting services — — — 98,401 — — 98,401 Construction materials — — — 207,910 — — 207,910 Intrasegment eliminations — — — (44,104) — — (44,104) Inside specialty contracting — — — — 372,209 — 372,209 Outside specialty contracting — — — — 130,150 — 130,150 Other 8,450 2,498 3,241 — 351 2,991 17,531 Intersegment eliminations (195) (185) (25,199) (63) (2,470) (2,973) (31,085) Revenues from contracts with customers 86,206 324,329 10,610 262,144 500,240 18 1,183,547 Revenues out of scope (298) 2,114 45 — 11,965 — 13,826 Total external operating revenues $ 85,908 $ 326,443 $ 10,655 $ 262,144 $ 512,205 $ 18 $ 1,197,373 Presented in the previous tables are intrasegment revenues within the construction materials and contracting segment to highlight the focus on vertical integration as this segment sells materials to both third parties and internal customers. Due to consolidation requirements, these revenues must be eliminated against construction materials to arrive at the external operating revenue total for the segment. Contract balances The timing of revenue recognition may differ from the timing of invoicing to customers. The timing of invoicing to customers does not necessarily correlate with the timing of revenues being recognized under the cost-to-cost method of accounting. Contracts from contracting services are billed as work progresses in accordance with agreed upon contractual terms. Generally, billing to the customer occurs contemporaneous to revenue recognition. A variance in timing of the billings may result in a contract asset or a contract liability. A contract asset occurs when revenues are recognized under the cost-to-cost measure of progress, which exceeds amounts billed on uncompleted contracts. Such amounts will be billed as standard contract terms allow, usually based on various measures of performance or achievement. A contract liability occurs when there are billings in excess of revenues recognized under the cost-to-cost measure of progress on uncompleted contracts. Contract liabilities decrease as revenue is recognized from the satisfaction of the related performance obligation. The changes in contract assets and liabilities were as follows: March 31, 2021 December 31, 2020 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 107,543 $ 104,345 $ 3,198 Receivables, net Contract liabilities - current (142,828) (158,603) 15,775 Accounts payable Contract liabilities - noncurrent (171) (52) (119) Noncurrent liabilities - other Net contract liabilities $ (35,456) $ (54,310) $ 18,854 The Company recognized $123.4 million in revenue for the three months ended March 31, 2021, which was previously included in contract liabilities at December 31, 2020. The Company recognized $89.4 million in revenue for the three months ended March 31, 2020, which was previously included in contract liabilities at December 31, 2019. The Company recognized a net increase in revenues of $34.3 million and $19.5 million for the three months ended March 31, 2021 and 2020, respectively, from performance obligations satisfied in prior periods. Remaining performance obligations The remaining performance obligations, also referred to as backlog, at the construction materials and contracting and construction services segments include unrecognized revenues that the Company reasonably expects to be realized. These unrecognized revenues can include: projects that have a written award, a letter of intent, a notice to proceed, an agreed upon work order to perform work on mutually accepted terms and conditions and change orders or claims to the extent management believes additional contract revenues will be earned and are deemed probable of collection. Excluded from remaining performance obligations are potential orders under master service agreements. The majority of the Company's construction contracts have an original duration of less than two years. The remaining performance obligations at the pipeline segment include firm transportation and storage contracts with fixed pricing and fixed volumes. The Company has applied the practical expedient, which does not require additional disclosures for contracts with an original duration of less than 12 months, to certain firm transportation and non-regulated contracts. The Company's firm transportation and firm storage contracts included in the remaining performance obligations have weighted average remaining durations of approximately five and one years, respectively. At March 31, 2021, the Company's remaining performance obligations were $2.2 billion. The Company expects to recognize the following revenue amounts in future periods related to these remaining performance obligations: $1.7 billion within the next 12 months or less; $283.8 million within the next 13 to 24 months; and $213.4 million in 25 months or more.

Business Combinations

Business Combinations	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Business Combinations	Business combinations The following acquisitions were accounted for as business combinations in accordance with ASC 805 - Business Combinations. The results of the acquired businesses have been included in the Consolidated Financial Statements beginning on the acquisition date. Pro forma financial amounts reflecting the effects of the business combinations are not presented, as none of these business combinations, individually or in the aggregate, were material to the Company's financial position or results of operations. The acquisitions are also subject to customary adjustments based on, among other things, the amount of cash, debt and working capital in the business as of the closing date. The amounts included in the Consolidated Balance Sheets for these adjustments are considered provisional until final settlement has occurred. In 2020, the construction materials and contracting segment made the following acquisitions: • The assets of McMurry Ready-Mix Co., an aggregates and concrete supplier in Wyoming, were acquired in December 2020. • The assets of Oldcastle Infrastructure Spokane, a prestressed-concrete business in Washington, were acquired in February 2020. In February 2020, the construction services segment acquired PerLectric, Inc., an electrical construction company in Virginia. The total purchase price for acquisitions that occurred in 2020 was $110.2 million, subject to certain adjustments, with cash acquired totaling $1.7 million. The purchase price includes consideration paid of $106.0 million and $2.5 million of indemnity holdback liabilities. The amounts allocated to the aggregated assets acquired and liabilities assumed during 2020 were as follows: $54.8 million to current assets; $27.1 million to property, plant and equipment; $33.6 million to goodwill; $19.0 million to other intangible assets; $22.6 million to current liabilities; $300,000 to noncurrent liabilities - other and $1.4 million to asset retirement obligations. As of December 31, 2020 and March 31, 2021, the purchase price adjustments had been settled and no material adjustments were made to the provisional accounting for Oldcastle Infrastructure Spokane and PerLectric, Inc., respectively. At March 31, 2021, the purchase price allocation for McMurry Ready-Mix Co. was preliminary and will be finalized within 12 months of the acquisition date. The Company issued debt to finance these acquisitions. Costs incurred for acquisitions are included in operation and maintenance expense on the Consolidated Statements of Income and were not material for the three months ended March 31, 2021 and 2020.

Leases

Leases	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Leases	Leases The Company's leases primarily include operating leases for equipment, buildings, easements and vehicles. The Company leases certain equipment to third parties through its utility and construction services segments, which are considered short-term operating leases with terms of less than 12 months. The Company recognized revenue from operating leases of $12.0 million and $12.1 million for the three months ended March 31, 2021 and 2020, respectively. At March 31, 2021, the Company had $10.4 million of lease receivables with a majority due within 12 months.

Goodwill and other intangible a

Goodwill and other intangible assets	3 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and other intangible assets	Goodwill and other intangible assets The changes in the carrying amount of goodwill were as follows: Balance at January 1, 2021 Goodwill Measurement Balance at March 31, 2021 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 226,003 — — 226,003 Construction services 143,224 — — 143,224 Total $ 714,963 $ — $ — $ 714,963 Balance at January 1, 2020 Goodwill Measurement Balance at March 31, 2020 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 217,234 6,483 — 223,717 Construction services 118,388 25,686 — 144,074 Total $ 681,358 $ 32,169 $ — $ 713,527 Balance at January 1, 2020 Goodwill Measurement Balance at December 31, 2020 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 217,234 8,778 (9) 226,003 Construction services 118,388 24,436 400 143,224 Total $ 681,358 $ 33,214 $ 391 $ 714,963 Other amortizable intangible assets were as follows: March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Customer relationships $ 28,836 $ 30,087 $ 28,836 Less accumulated amortization 7,792 4,138 6,887 21,044 25,949 21,949 Noncompete agreements 3,941 4,229 3,941 Less accumulated amortization 2,441 1,928 2,309 1,500 2,301 1,632 Other 11,957 13,060 12,927 Less accumulated amortization 10,540 7,060 11,012 1,417 6,000 1,915 Total $ 23,961 $ 34,250 $ 25,496 The previous tables include goodwill and intangible assets associated with the business combinations completed during 2020. For more information related to these business combinations, see Note 10. Amortization expense for amortizable intangible assets for the three months ended March 31, 2021 and 2020, was $1.5 million and $2.0 million, respectively. Estimated amortization expense for identifiable intangible assets as of March 31, 2021, was: Remainder of 2021 2022 2023 2024 2025 Thereafter (In thousands) Amortization expense $ 3,377 $ 4,394 $ 4,121 $ 3,799 $ 1,862 $ 6,408

Regulatory assets and liabiliti

Regulatory assets and liabilities	3 Months Ended
	Mar. 31, 2021
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	Regulatory assets and liabilities The following table summarizes the individual components of unamortized regulatory assets and liabilities: Estimated Recovery or Refund Period as of March 31, 2021 * March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 76,782 $ 39,805 $ 42,481 Cost recovery mechanisms Up to 1 year 7,130 6,686 10,645 Conservation programs Up to 1 year 6,679 6,303 7,117 Other Up to 1 year 7,861 2,412 8,284 98,452 55,206 68,527 Noncurrent: Pension and postretirement benefits ** 155,924 157,051 155,942 Plant retirement - 73,498 41,080 65,919 Plant costs/asset retirement obligations Over plant lives 72,250 67,475 71,740 Manufactured gas plant site remediation - 26,002 15,699 26,429 Cost recovery mechanisms Up to 10 years 15,508 11,891 16,245 Natural gas costs recoverable through rate adjustments Up to 3 years 15,158 33,027 21,539 Taxes recoverable from customers Over plant lives 10,800 11,082 10,785 Long-term debt refinancing costs Up to 39 years 4,268 4,133 4,426 Other Up to 18 years 6,509 6,751 6,356 379,917 348,189 379,381 Total regulatory assets $ 478,369 $ 403,395 $ 447,908 Regulatory liabilities: Current: Natural gas costs refundable through rate adjustments Up to 1 year $ 16,344 $ 32,181 $ 18,565 Taxes refundable to customers Up to 1 year 3,092 4,002 3,557 Electric fuel and purchased power deferral Up to 1 year 2,001 7,188 3,667 Other Up to 1 year 12,829 16,701 5,661 34,266 60,072 31,450 Noncurrent: Taxes refundable to customers Over plant lives 224,795 240,148 227,850 Plant removal and decommissioning costs Over plant lives 169,430 174,120 167,171 Pension and postretirement benefits ** 16,965 18,040 16,989 Other Up to 21 years 17,870 10,897 16,065 429,060 443,205 428,075 Total regulatory liabilities $ 463,326 $ 503,277 $ 459,525 Net regulatory position $ 15,043 $ (99,882) $ (11,617) * Estimated recovery or refund period for amounts currently being recovered or refunded in rates charged to customers. ** Recovered as expense is incurred or cash contributions are made. At March 31, 2021 and 2020, and December 31, 2020, approximately $361.4 million, $285.8 million and $332.5 million, respectively, of regulatory assets were not earning a rate of return; however, these regulatory assets are expected to be recovered from customers in future rates. These assets are largely comprised of the unfunded portion of pension and postretirement benefits, asset retirement obligations, accelerated depreciation on plant to be retired and the estimated future cost of manufactured gas plant site remediation. In February 2021, a prolonged period of unseasonably cold temperatures in the central United States significantly increased the demand for electric and natural gas services and contributed to increased market prices. Overall, Montana-Dakota and Great Plains incurred approximately $44.0 million in increased natural gas costs in February 2021 in order to maintain services for its customers. The Company has filed out-of-cycle purchased gas adjustment requests in four out of five jurisdictions affected by this cold-weather event, as discussed in Note 19, and will continue to engage with its regulators to determine the appropriate recovery periods over which to recover the associated natural gas costs. In 2019, the Company experienced increased natural gas costs in Washington from the rupture of the Enbridge pipeline in Canada in late 2018. As a result, the Company requested, and the WUTC approved, recovery of the balance of natural gas costs recoverable related to this period of time over three years rather than its normal one-year recovery period. In February 2019, the Company announced the retirement of three aging coal-fired electric generating units. The Company has accelerated the depreciation related to these facilities in property, plant and equipment and has recorded the difference between the accelerated depreciation, in accordance with GAAP, and the depreciation approved for rate-making purposes as regulatory assets. The first unit ceased operations on March 31, 2021, and as discussed in Note 19, requests have been filed with the NDPSC and SDPUC to offset the savings associated with the cessation of operations of this unit with the amortization of the deferred regulatory assets. The remaining two units are expected to be retired in early 2022. The Company expects to recover the regulatory assets related to the plant retirements in future rates. If, for any reason, the Company's regulated businesses cease to meet the criteria for application of regulatory accounting for all or part of their operations, the regulatory assets and liabilities relating to those portions ceasing to meet such criteria would be removed from the balance sheet and included in the statement of income or accumulated other comprehensive income (loss) in the period in which the discontinuance of regulatory accounting occurs.

Fair value measurements

Fair value measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair value measurements	Fair value measurements The Company measures its investments in certain fixed-income and equity securities at fair value with changes in fair value recognized in income. The Company anticipates using these investments, which consist of insurance contracts, to satisfy its obligations under its unfunded, nonqualified defined benefit and defined contribution plans for executive officers and certain key management employees, and invests in these fixed-income and equity securities for the purpose of earning investment returns and capital appreciation. These investments, which totaled $101.6 million, $83.3 million and $100.1 million, at March 31, 2021 and 2020, and December 31, 2020, respectively, are classified as investments on the Consolidated Balance Sheets. The net unrealized gains on these investments was $127,000 for the three months ended March 31, 2021. The net unrealized loss on these investments was $3.7 million for the three months ended March 31, 2020. The change in fair value, which is considered part of the cost of the plan, is classified in other income on the Consolidated Statements of Income. The Company did not elect the fair value option, which records gains and losses in income, for its available-for-sale securities, which include mortgage-backed securities and U.S. Treasury securities. These available-for-sale securities are recorded at fair value and are classified as investments on the Consolidated Balance Sheets. Unrealized gains or losses are recorded in accumulated other comprehensive income (loss). Details of available-for-sale securities were as follows: March 31, 2021 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 8,709 $ 155 $ 10 $ 8,854 U.S. Treasury securities 2,636 — 14 2,622 Total $ 11,345 $ 155 $ 24 $ 11,476 March 31, 2020 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,691 $ 236 $ — $ 9,927 U.S. Treasury securities 1,173 12 — 1,185 Total $ 10,864 $ 248 $ — $ 11,112 December 31, 2020 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,799 $ 156 $ 9 $ 9,946 U.S. Treasury securities 1,386 — 5 1,381 Total $ 11,185 $ 156 $ 14 $ 11,327 Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. The fair value ASC establishes a hierarchy for grouping assets and liabilities, based on the significance of inputs. The estimated fair values of the Company's assets and liabilities measured on a recurring basis are determined using the market approach. The Company's money market funds are valued at the net asset value of shares held at the end of the quarter, based on published market quotations on active markets, or using other known sources including pricing from outside sources. The estimated fair value of the Company's mortgage-backed securities and U.S. Treasury securities are based on comparable market transactions, other observable inputs or other sources, including pricing from outside sources. The estimated fair value of the Company's insurance contracts are based on contractual cash surrender values that are determined primarily by investments in managed separate accounts of the insurer. These amounts approximate fair value. The managed separate accounts are valued based on other observable inputs or corroborated market data. Though the Company believes the methods used to estimate fair value are consistent with those used by other market participants, the use of other methods or assumptions could result in a different estimate of fair value. The Company's assets measured at fair value on a recurring basis were as follows: Fair Value Measurements at March 31, 2021, Using Quoted Prices in Significant Significant Balance at March 31, 2021 (In thousands) Assets: Money market funds $ 9,388 $ — $ 9,388 Insurance contracts* — 101,632 101,632 Available-for-sale securities: Mortgage-backed securities — 8,854 — 8,854 U.S. Treasury securities — 2,622 — 2,622 Total assets measured at fair value $ — $ 122,496 $ — $ 122,496 * The insurance contracts invest approximately 54 percent in fixed-income investments, 19 percent in common stock of large-cap companies, 10 percent in common stock of mid-cap companies, 9 percent in common stock of small-cap companies, 6 percent in target date investments and 2 percent in cash equivalents. Fair Value Measurements at March 31, 2020, Using Quoted Prices in Significant Significant Balance at March 31, 2020 (In thousands) Assets: Money market funds $ — $ 8,470 $ — $ 8,470 Insurance contract* — 83,254 — 83,254 Available-for-sale securities: Mortgage-backed securities — 9,927 — 9,927 U.S. Treasury securities — 1,185 — 1,185 Total assets measured at fair value $ — $ 102,836 $ — $ 102,836 * The insurance contract invests approximately 58 percent in fixed-income investments, 20 percent in common stock of large-cap companies, 8 percent in common stock of mid-cap companies, 8 percent in common stock of small-cap companies, 4 percent in target date investments and 2 percent in cash equivalents. Fair Value Measurements at December 31, 2020, Using Quoted Prices in Significant Significant Balance at December 31, 2020 (In thousands) Assets: Money market funds $ — $ 8,917 $ — $ 8,917 Insurance contract* — 100,104 — 100,104 Available-for-sale securities: Mortgage-backed securities — 9,946 — 9,946 U.S. Treasury securities — 1,381 — 1,381 Total assets measured at fair value $ — $ 120,348 $ — $ 120,348 * The insurance contract invests approximately 57 percent in fixed-income investments, 18 percent in common stock of large-cap companies, 9 percent in common stock of mid-cap companies, 9 percent in common stock of small-cap companies, 5 percent in target date investments and 2 percent in cash equivalents. The Company applies the provisions of the fair value measurement standard to its nonrecurring, non-financial measurements, including long-lived asset impairments. These assets are not measured at fair value on an ongoing basis but are subject to fair value adjustments only in certain circumstances. The Company reviews the carrying value of its long-lived assets, excluding goodwill, whenever events or changes in circumstances indicate that such carrying amounts may not be recoverable. The Company performed fair value assessments of the assets acquired and liabilities assumed in the business combinations that occurred during 2020. The fair value of these assets and liabilities were determined based on Level 2 and Level 3 inputs. The estimated fair value of the Company's Level 2 commodity derivative instruments is based on futures prices, volatility and time to maturity, among other things. Counterparty statements are utilized to determine the value of the commodity derivative instruments and are reviewed and corroborated using various methodologies and significant observable inputs. The Company's and the counterparties' nonperformance risk is also evaluated . The Company's long-term debt is not measured at fair value on the Consolidated Balance Sheets and the fair value is being provided for disclosure purposes only. The fair value was categorized as Level 2 in the fair value hierarchy and was based on discounted future cash flows using current market interest rates. The estimated fair value of the Company's Level 2 long-term debt was as follows: March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Carrying amount $ 2,253,274 $ 2,455,235 $ 2,213,130 Fair value $ 2,473,806 $ 2,618,297 $ 2,537,289 The carrying amounts of the Company's remaining financial instruments included in current assets and current liabilities approximate their fair values .

Debt

Debt	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Debt	Debt Certain debt instruments of the Company's subsidiaries contain restrictive and financial covenants and cross-default provisions. In order to borrow under the debt agreements, the subsidiary companies must be in compliance with the applicable covenants and certain other conditions, all of which the subsidiaries, as applicable, were in compliance with at March 31, 2021. In the event the subsidiaries do not comply with the applicable covenants and other conditions, alternative sources of funding may need to be pursued. Montana-Dakota's and Centennial's respective commercial paper programs are supported by revolving credit agreements. While the amount of commercial paper outstanding does not reduce available capacity under the respective revolving credit agreements, Montana-Dakota and Centennial do not issue commercial paper in an aggregate amount exceeding the available capacity under the credit agreements. The commercial paper borrowings may vary during the period, largely the result of fluctuations in working capital requirements due to the seasonality of certain operations of the Company's subsidiaries. Long-term debt Long-term Debt Outstanding Long-term debt outstanding was as follows: Weighted Average Interest Rate at March 31, 2021 March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Senior Notes due on dates ranging from October 22, 2022 to October 30, 2060 4.40 % $ 1,950,000 $ 1,850,000 $ 1,950,000 Commercial paper supported by revolving credit agreements .33 % 218,900 265,000 125,600 Credit agreements due on June 7, 2024 2.20 % 43,350 259,550 95,900 Medium-Term Notes due on dates ranging from September 15, 2027 to March 16, 2029 7.32 % 35,000 50,000 35,000 Term Loan Agreement due on September 3, 2032 2.00 % 8,400 9,100 8,400 Other notes due on dates ranging from July 15, 2021 to July 1, 2061 .82 % 3,282 28,374 4,034 Less unamortized debt issuance costs 5,655 6,640 5,803 Less discount 3 149 1 Total long-term debt 2,253,274 2,455,235 2,213,130 Less current maturities 1,552 16,560 1,555 Net long-term debt $ 2,251,722 $ 2,438,675 $ 2,211,575 Schedule of Debt Maturities Long-term debt maturities, which excludes unamortized debt issuance costs and discount, at March 31, 2021, were as follows: Remainder of 2022 2023 2024 2025 Thereafter (In thousands) Long-term debt maturities $ 780 $ 148,021 $ 77,921 $ 323,672 $ 177,802 $ 1,530,736

Cash flow information

Cash flow information	3 Months Ended
	Mar. 31, 2021
Supplemental Cash Flow Information [Abstract]
Cash flow information	Cash flow information Cash expenditures for interest and income taxes were as follows: Three Months Ended March 31, 2021 2020 (In thousands) Interest, net* $ 14,303 $ 15,978 Income taxes paid (refunded), net $ 13,880 $ (1) * AFUDC - borrowed was $348,000 and $627,000 for the three months ended March 31, 2021 and 2020, respectively. Noncash investing and financing transactions were as follows: March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 9,236 $ 10,655 $ 54,356 Property, plant and equipment additions in accounts payable $ 20,594 $ 27,425 $ 26,082 Accrual for holdback payment related to a business combination $ — $ 5,000 $ 2,500

Business segment data

Business segment data	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Business segment data	Business segment data The Company's reportable segments are those that are based on the Company's method of internal reporting, which generally segregates the strategic business units due to differences in products, services and regulation. The internal reporting of these operating segments is defined based on the reporting and review process used by the Company's chief executive officer. The Company's operations are located within the United States. The electric segment generates, transmits and distributes electricity in Montana, North Dakota, South Dakota and Wyoming. The natural gas distribution segment distributes natural gas in those states, as well as in Idaho, Minnesota, Oregon and Washington. These operations also supply related value-added services. The pipeline segment provides natural gas transportation and underground storage services through a regulated pipeline system primarily in the Rocky Mountain and northern Great Plains regions of the United States. This segment also provides non-regulated cathodic protection and other energy-related services. In 2020, the pipeline segment divested its regulated and non-regulated natural gas gathering assets. With the completion of these sales, the segment exited the natural gas gathering business. The construction materials and contracting segment mines, processes and sells construction aggregates (crushed stone, sand and gravel); produces and sells asphalt mix; and supplies ready-mixed concrete. This segment focuses on vertical integration of its contracting services with its construction materials to support the aggregate-based product lines including aggregate placement, asphalt and concrete paving, and site development and grading. Although not common to all locations, other products include the sale of cement, liquid asphalt for various commercial and roadway applications, various finished concrete products and other building materials and related contracting services. This segment operates in the central, southern and western United States, as well as Alaska and Hawaii. The construction services segment provides inside and outside specialty contracting services in 44 states plus Washington D.C. Its inside services include design, construction and maintenance of electrical and communication wiring and infrastructure, fire suppression systems, and mechanical piping and services. Its outside services include design, construction and maintenance of overhead and underground electrical distribution and transmission lines, substations, external lighting, traffic signalization, and gas pipelines, as well as utility excavation and the manufacture and distribution of transmission line construction equipment. This segment also constructs and maintains renewable energy projects. These specialty contracting services are provided to utilities and large manufacturing, commercial, industrial, institutional and governmental customers. The Other category includes the activities of Centennial Capital, which, through its subsidiary InterSource Insurance Company, insures various types of risks as a captive insurer for certain of the Company's subsidiaries. The function of the captive insurer is to fund the self-insured layers of the insured Company's general liability, automobile liability, pollution liability and other coverages. Centennial Capital also owns certain real and personal property. In addition, the Other category includes certain assets, liabilities and tax adjustments of the holding company primarily associated with corporate functions and certain general and administrative costs (reflected in operation and maintenance expense) and interest expense, which were previously allocated to the refining business and Fidelity and do not meet the criteria for income (loss) from discontinued operations. The Other category also includes Centennial Resources' former investment in Brazil. Discontinued operations include the results and supporting activities of Fidelity other than certain general and administrative costs and interest expense as described above. The information below follows the same accounting policies as described in Note 2 of the Notes to Consolidated Financial Statements in the 2020 Annual Report. Information on the Company's segments was as follows: Three Months Ended March 31, 2021 2020 (In thousands) External operating revenues: Regulated operations: Electric $ 84,673 $ 85,908 Natural gas distribution 350,206 326,443 Pipeline 7,502 6,331 442,381 418,682 Non-regulated operations: Pipeline 2,411 4,324 Construction materials and contracting 265,659 262,144 Construction services 517,470 512,205 Other 17 18 785,557 778,691 Total external operating revenues $ 1,227,938 $ 1,197,373 Three Months Ended March 31, 2021 2020 (In thousands) Intersegment operating revenues: Regulated operations: Electric $ 136 $ 195 Natural gas distribution 142 185 Pipeline 25,990 25,183 26,268 25,563 Non-regulated operations: Pipeline 239 16 Construction materials and contracting 62 63 Construction services 1,042 2,470 Other 3,324 2,973 4,667 5,522 Intersegment eliminations (30,935) (31,085) Total intersegment operating revenues $ — $ — Operating income (loss): Electric $ 13,865 $ 14,859 Natural gas distribution 53,573 49,998 Pipeline 12,536 11,419 Construction materials and contracting (34,889) (43,269) Construction services 40,277 23,796 Other (198) 267 Total operating income $ 85,164 $ 57,070 Net income (loss): Regulated operations: Electric $ 10,749 $ 11,374 Natural gas distribution 36,178 32,369 Pipeline 9,194 7,386 56,121 51,129 Non-regulated operations: Pipeline (296) (13) Construction materials and contracting (30,813) (38,215) Construction services 29,825 16,823 Other (2,721) (4,185) (4,005) (25,590) Income from continuing operations 52,116 25,539 Income (loss) from discontinued operations, net of tax 15 (409) Net income $ 52,131 $ 25,130

Employee benefit plans

Employee benefit plans	3 Months Ended
	Mar. 31, 2021
Retirement Benefits [Abstract]
Employee benefit plans	Employee benefit plans Pension and other postretirement plans The Company has noncontributory qualified defined benefit pension plans and other postretirement benefit plans for certain eligible employees. Components of net periodic benefit cost (credit) for the Company's pension and other postretirement benefit plans were as follows: Pension Benefits Other Three Months Ended March 31, 2021 2020 2021 2020 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 400 $ 352 Interest cost 2,455 2,973 466 591 Expected return on assets (4,894) (4,761) (1,275) (1,248) Amortization of prior service credit — — (349) (297) Amortization of net actuarial loss 2,004 1,863 6 2 Net periodic benefit cost (credit), including amount capitalized (435) 75 (752) (600) Less amount capitalized — — 39 32 Net periodic benefit cost (credit) $ (435) $ 75 $ (791) $ (632) The components of net periodic benefit cost (credit), other than the service cost component, are included in other income on the Consolidated Statements of Income. The service cost component is included in operation and maintenance expense on the Consolidated Statements of Income. Nonqualified defined benefit plans In addition to the qualified defined benefit pension plans reflected in the table at the beginning of this note, the Company also has unfunded, nonqualified defined benefit plans for executive officers and certain key management employees. The Company's net periodic benefit cost for these plans was $769,000 and $1.0 million for the three months ended March 31, 2021 and 2020, respectively. The components of net periodic benefit cost for these plans are included in other income on the Consolidated Statements of Income.

Regulatory matters

Regulatory matters	3 Months Ended
	Mar. 31, 2021
Regulated Operations [Abstract]
Regulatory Matters	Regulatory matters The Company regularly reviews the need for electric and natural gas rate changes in each of the jurisdictions in which service is provided. The Company files for rate adjustments to seek recovery of operating costs and capital investments, as well as reasonable returns as allowed by regulators. Certain regulatory proceedings and cases may also contain recurring mechanisms that can have an annual true-up. Examples of these recurring mechanisms include: infrastructure riders, transmission trackers, renewable resource cost adjustment riders, as well as weather normalization and decoupling mechanisms. The following paragraphs summarize the Company's significant open regulatory proceedings and cases by jurisdiction including updates to those reported in the 2020 Annual Report. The Company is unable to predict the ultimate outcome of these matters, the timing of final decisions of the various regulators and courts, or the effect on the Company's results of operations, financial position or cash flows. IPUC On January 12, 2021, Intermountain filed an application with the IPUC for a decrease in its depreciation and amortization rates of approximately $2.9 million annually or a decrease from a combined rate of 3.0 percent to 2.6 percent. Intermountain has requested the rates be retroactive to January 1, 2021. This matter is pending before the IPUC. MNPUC On September 27, 2019, Great Plains filed an application with the MNPUC for a natural gas rate increase of approximately $2.9 million annually or approximately 12.0 percent above current rates. The requested increase was primarily to recover investments in facilities to enhance safety and reliability and the depreciation and taxes associated with the increase in investment. On November 22, 2019, Great Plains received approval to implement an interim rate increase of approximately $2.6 million or approximately 11.0 percent, subject to refund, effective January 1, 2020. On October 26, 2020, the MNPUC issued an order authorizing an annual increase in revenues of approximately $2.6 million or approximately 11.5 percent. On February 25, 2021, the MNPUC approved implementing the rates effective April 1, 2021. Great Plains defers the difference between the actual cost of gas spent to serve customers and that recovered from customers on a monthly basis. Annually the Company prepares a true-up pursuant to the purchased gas adjustment tariff. On March 30, 2021, Great Plains filed an out-of-cycle cost of gas adjustment with the MNPUC for the recovery of approximately $11.1 million. The requested increase was for the February 2021 extreme cold weather, primarily in the central United States, and market conditions surrounding the natural gas commodity market. The length of recovery was requested at 28 months with a rate structure that is higher in the summer and lower in the winter due to the lower gas usage in the summer to mitigate the impact on customers. This matter is pending before the MNPUC. NDPSC On August 26, 2020, Montana-Dakota filed an application with the NDPSC for a natural gas rate increase of approximately $9.0 million annually or approximately 7.8 percent above current rates. The requested increase was primarily to recover investments in facilities to enhance system safety and reliability and the depreciation and taxes associated with the increase in investment. On December 16, 2020, Montana-Dakota received approval to implement an interim rate increase of approximately $6.9 million or approximately 6.0 percent, subject to refund, effective January 1, 2021. A hearing was held March 17 and 18, 2021. On April 9, 2021, Montana-Dakota, NDPSC Advocacy Staff and the intervener in the case filed a settlement agreement reflecting an updated increase of approximately $6.9 million annually or approximately 6.0 percent above current rates. On May 5, 2021, the NDPSC approved the settlement agreement with rates effective June 1, 2021. On March 2, 2021, Montana-Dakota filed an informational update to the generation resource recovery rider with the NDPSC related to the retirement of Unit 1 at Lewis & Clark Station. The filing includes the annual revenue requirement offset by the related amortization of the accelerated depreciation on the plant, net of excess deferred income taxes, and the decommissioning costs projected to be incurred in 2021 resulting in no impact to customers. Montana-Dakota defers the difference between the actual cost of gas spent to serve customers and that recovered from customers on a monthly basis. Annually the Company prepares a true-up pursuant to the purchased gas adjustment tariff. On March 31, 2021, Montana-Dakota filed an out-of-cycle cost of gas adjustment with the NDPSC for approximately $13.5 million. The requested increase was for the February 2021 extreme cold weather, primarily in the central United States, and market conditions surrounding the natural gas commodity market. The filing was made to expedite recovery of these costs and maintain the timing of annual purchased gas adjustment filings. This matter is pending before the NDPSC. SDPUC Montana-Dakota has a transmission cost recovery rider that allows annual updates to rates for actual costs for transmission-related projects and services. On March 1, 2021, Montana-Dakota filed an annual update to its transmission cost recovery rider to recover a revenue requirement of approximately $1.0 million annually, which reflects a true-up of the prior period adjustment, resulting in an increase in current rates of approximately $274,000. On April 30, 2021, the SDPUC approved the rates as requested with an effective date of May 1, 2021. Montana-Dakota has an infrastructure rider rate tariff that allows for annual adjustments for recent projected capital costs and related expenses for projects determined to be recoverable under the electric tariff. On February 26, 2021, Montana-Dakota filed an annual update to its infrastructure rider requesting to recover a revenue requirement of approximately $1.0 million annually, which reflects a true-up of the prior period adjustment, resulting in a decrease in current rates of approximately $236,000. On April 30, 2021, the SDPUC approved the rates as requested with an effective date of May 1, 2021. On March 11, 2021, Montana-Dakota filed an informational update to the infrastructure rider rate tariff with the SDPUC related to the retirement of Unit 1 at Lewis & Clark Station. The filing includes the annual revenue requirement offset by the related amortization of the accelerated depreciation on the plant, net of excess deferred income taxes, and the decommissioning costs projected to be incurred in 2021 resulting in no impact to customers. This matter is pending before the SDPUC. Montana-Dakota defers the difference between the actual cost of gas spent to serve customers and that recovered from customers on a monthly basis. Annually the Company prepares a true-up pursuant to the purchased gas cost adjustment tariff. On March 31, 2021, Montana-Dakota filed an out-of-cycle cost of gas adjustment with the SDPUC for approximately $5.5 million. The requested increase was for the February 2021 extreme cold weather, primarily in the central United States, and market conditions surrounding the natural gas commodity market. The filing was made to expedite recovery of these costs and maintain the timing of annual purchased gas adjustment filings. On April 30, 2021, the SDPUC approved the rates as requested with an effective date of May 1, 2021. WUTC On June 19, 2020, Cascade filed an application with the WUTC for a natural gas rate increase of approximately $13.8 million annually or approximately 5.3 percent above current rates. The requested increase was primarily to recover investments made in infrastructure upgrades, as well as increased operation and maintenance costs. Cascade updated its filing on July 24, 2020, to approximately $14.3 million annually or approximately 5.5 percent. Cascade filed a rebuttal case on January 8, 2021, supporting an increase of approximately $7.4 million annually or approximately 2.8 percent. The revised revenue within the rebuttal case reflects several adjustments including depreciation, reduction to return on equity, delays on certain projects, adjustments to income taxes and updates to wages. A hearing was held February 24, 2021, and briefs were filed with the WUTC on March 22, 2021. The WUTC has 11 months to render a final decision on the rate case. This matter is pending before the WUTC. WYPSC On May 14, 2020, Montana-Dakota filed separate requests for its electric and natural gas services with the WYPSC to use deferred accounting for costs related to the COVID-19 pandemic. Montana-Dakota determined the deferred accounting orders were no longer needed and the filings were withdrawn by Montana-Dakota on March 2, 2021.

Contingencies

Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Contingencies The Company is party to claims and lawsuits arising out of its business and that of its consolidated subsidiaries, which may include, but are not limited to, matters involving property damage, personal injury, and environmental, contractual, statutory and regulatory obligations. The Company accrues a liability for those contingencies when the incurrence of a loss is probable and the amount can be reasonably estimated. If a range of amounts can be reasonably estimated and no amount within the range is a better estimate than any other amount, then the minimum of the range is accrued. The Company does not accrue liabilities when the likelihood that the liability has been incurred is probable but the amount cannot be reasonably estimated or when the liability is believed to be only reasonably possible or remote. For contingencies where an unfavorable outcome is probable or reasonably possible and which are material, the Company discloses the nature of the contingency and, in some circumstances, an estimate of the possible loss. Accruals are based on the best information available, but in certain situations management is unable to estimate an amount or range of a reasonably possible loss including, but not limited to when: (1) the damages are unsubstantiated or indeterminate, (2) the proceedings are in the early stages, (3) numerous parties are involved, or (4) the matter involves novel or unsettled legal theories. At March 31, 2021 and 2020, and December 31, 2020, the Company accrued liabilities which have not been discounted, including liabilities held for sale, of $55.0 million, $33.1 million and $41.5 million, respectively. At March 31, 2021 and 2020, and December 31, 2020, the Company also recorded corresponding insurance receivables of $31.6 million, $19.0 million and $17.5 million, respectively, and regulatory assets of $20.9 million, $10.8 million and $21.3 million, respectively, related to the accrued liabilities. The accruals are for contingencies, including litigation, production taxes, royalty claims and environmental matters. This includes amounts that have been accrued for matters discussed in Environmental matters within this note. The Company will continue to monitor each matter and adjust accruals as might be warranted based on new information and further developments. Management believes that the outcomes with respect to probable and reasonably possible losses in excess of the amounts accrued, net of insurance recoveries, while uncertain, either cannot be estimated or will not have a material effect upon the Company's financial position, results of operations or cash flows. Unless otherwise required by GAAP, legal costs are expensed as they are incurred. Environmental matters The Company is a party to claims for the cleanup of environmental contamination at certain manufactured gas plant sites, as well as a superfund site. There were no material changes to the Company's environmental matters that were previously reported in the 2020 Annual Report. Guarantees In 2009, multiple sale agreements were signed to sell the Company's ownership interests in the Brazilian Transmission Lines. In connection with the sale, Centennial agreed to guarantee payment of any indemnity obligations of certain of the Company's indirect wholly owned subsidiaries. The remaining guarantee is expected to expire in 2021. The guarantees were required by the buyers as a condition to the sale of the Brazilian Transmission Lines. Certain subsidiaries of the Company have outstanding guarantees to third parties that guarantee the performance of other subsidiaries of the Company. These guarantees are related to construction contracts, insurance deductibles and loss limits, and certain other guarantees. At March 31, 2021, the fixed maximum amounts guaranteed under these agreements aggregated $235.8 million. Certain of the guarantees also have no fixed maximum amounts specified. At March 31, 2021, the amounts of scheduled expiration of the maximum amounts guaranteed under these agreements aggregate to $120.8 million in 2021; $42.4 million in 2022; $61.9 million in 2023; $500,000 in 2024; $500,000 in 2025; $700,000 thereafter; and $9.0 million, which has no scheduled maturity date. There were no amounts outstanding under the previously mentioned guarantees at March 31, 2021. In the event of default under these guarantee obligations, the subsidiary issuing the guarantee for that particular obligation would be required to make payments under its guarantee. Certain subsidiaries have outstanding letters of credit to third parties related to insurance policies and other agreements, some of which are guaranteed by other subsidiaries of the Company. At March 31, 2021, the fixed maximum amounts guaranteed under these letters of credit aggregated $25.5 million. At March 31, 2021, the amounts of scheduled expiration of the maximum amounts guaranteed under these letters of credit aggregate to $23.6 million in 2021 and $1.9 million in 2022. There were no amounts outstanding under the previously mentioned letters of credit at March 31, 2021. In the event of default under these letter of credit obligations, the subsidiary guaranteeing the letter of credit would be obligated for reimbursement of payments made under the letter of credit. In addition, Centennial, Knife River and MDU Construction Services have issued guarantees to third parties related to the routine purchase of maintenance items, materials and lease obligations for which no fixed maximum amounts have been specified. These guarantees have no scheduled maturity date. In the event a subsidiary of the Company defaults under these obligations, Centennial, Knife River or MDU Construction Services would be required to make payments under these guarantees. Any amounts outstanding by subsidiaries of the Company were reflected on the Consolidated Balance Sheet at March 31, 2021. In the normal course of business, Centennial has surety bonds related to construction contracts and reclamation obligations of its subsidiaries. In the event a subsidiary of Centennial does not fulfill a bonded obligation, Centennial would be responsible to the surety bond company for completion of the bonded contract or obligation. A large portion of the surety bonds is expected to expire within the next 12 months; however, Centennial will likely continue to enter into surety bonds for its subsidiaries in the future. At March 31, 2021, approximately $1.1 billion of surety bonds were outstanding, which were not reflected on the Consolidated Balance Sheet. Variable interest entities The Company evaluates its arrangements and contracts with other entities to determine if they are VIEs and if so, if the Company is the primary beneficiary. Fuel Contract Coyote Station entered into a coal supply agreement with Coyote Creek that provides for the purchase of coal necessary to supply the coal requirements of the Coyote Station for the period May 2016 through December 2040. Coal purchased under the coal supply agreement is reflected in inventories on the Consolidated Balance Sheets and is recovered from customers as a component of electric fuel and purchased power. The coal supply agreement creates a variable interest in Coyote Creek due to the transfer of all operating and economic risk to the Coyote Station owners, as the agreement is structured so that the price of the coal will cover all costs of operations, as well as future reclamation costs. The Coyote Station owners are also providing a guarantee of the value of the assets of Coyote Creek as they would be required to buy the assets at book value should they terminate the contract prior to the end of the contract term and are providing a guarantee of the value of the equity of Coyote Creek in that they are required to buy the entity at the end of the contract term at equity value. Although the Company has determined that Coyote Creek is a VIE, the Company has concluded that it is not the primary beneficiary of Coyote Creek because the authority to direct the activities of the entity is shared by the four unrelated owners of the Coyote Station, with no primary beneficiary existing. As a result, Coyote Creek is not required to be consolidated in the Company's financial statements. At March 31, 2021, the Company's exposure to loss as a result of the Company's involvement with the VIE, based on the Company's ownership percentage, was $33.1 million.

Basis of presentation (Policies

Basis of presentation (Policies)	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of presentation	The accompanying consolidated interim financial statements were prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Interim financial statements do not include all disclosures provided in annual financial statements and, accordingly, these financial statements should be read in conjunction with those appearing in the 2020 Annual Report. The information is unaudited but includes all adjustments that are, in the opinion of management, necessary for a fair presentation of the accompanying consolidated interim financial statements and are of a normal recurring nature. Depreciation, depletion and amortization expense is reported separately on the Consolidated Statements of Income and therefore is excluded from the other line items within operating expenses.

New accounting standards (Polic

New accounting standards (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Standards Update and Change in Accounting Principle [Abstract]
New accounting standards	Recently adopted accounting standards ASU 2018-14 - Changes to the Disclosure Requirements for Defined Benefit Plans In August 2018, the FASB issued guidance on modifying the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans as part of the disclosure framework project. The guidance removes disclosures that are no longer considered cost beneficial, clarifies the specific requirements of disclosures and adds disclosure requirements identified as relevant. The guidance adds, among other things, the requirement to include an explanation for significant gains and losses related to changes in benefit obligations for the period. The guidance removes, among other things, the disclosure requirement to disclose the amount of net periodic benefit costs to be amortized over the next fiscal year from accumulated other comprehensive income (loss) and the effects a one percentage point change in assumed health care cost trend rates will have on certain benefit components. The Company adopted the guidance on January 1, 2021, on a retrospective basis. The Company determined the new guidance will not materially impact its consolidated financial statement disclosures. ASU 2019-12 - Simplifying the Accounting for Income Taxes In December 2019, the FASB issued guidance on simplifying the accounting for income taxes by removing certain exceptions in ASC 740 and providing simplification amendments. The guidance removes exceptions on intraperiod tax allocations and reporting and provides simplification on accounting for franchise taxes, tax basis goodwill and tax law changes. The Company adopted the guidance on January 1, 2021, and determined it did not have a material impact on its results of operations, financial position, cash flows or disclosures. Recently issued accounting standards not yet adopted ASU 2020-04 - Reference Rate Reform In March 2020, the FASB issued optional guidance to ease the facilitation of the effects of reference rate reform on financial reporting. The guidance applies to certain contract modifications, hedging relationships and other transactions that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. LIBOR is expected to be retired with a full phase-out by the end of 2021 and replaced by a new reference rate, which includes SOFR. The guidance can be applied beginning in the interim period that includes March 12, 2020, and cannot be applied to contract modifications or hedging relationships entered into or evaluated after December 31, 2022. The Company has updated its credit agreements to include language regarding the successor or alternate rate to LIBOR, and a review of other contracts and agreements is on-going. The Company does not expect the guidance to have a material impact on its results of operations, financial position, cash flows or disclosures.

Receivables and allowance for_2

Receivables and allowance for expected credit losses (Policies)	3 Months Ended
	Mar. 31, 2021
Credit Loss [Abstract]
Accounts receivable and allowance for doubtful accounts	Receivables consists primarily of trade receivables from the sale of goods and services, which are recorded at the invoiced amount, and contract assets, net of expected credit losses. For more information on contract assets, see Note 9. The Company's trade receivables are all due in 12 months or less.
Expected credit loss	The Company's expected credit losses are determined through a review using historical credit loss experience, changes in asset specific characteristics, current conditions and reasonable and supportable future forecasts, among other specific account data, and is performed at least quarterly. The Company develops and documents its methodology to determine its allowance for expected credit losses at each of its reportable business segments. Risk characteristics used by the business segments may include customer mix, knowledge of customers, general economic conditions of the various local economies and impacts of COVID-19, among others. Specific account balances are written off when management determines the amounts to be uncollectible.

Inventories and natural gas i_2

Inventories and natural gas in storage (Policies)	3 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Inventories and natural gas in storage	Natural gas in storage for the Company's regulated operations is generally valued at lower of cost or market using the last-in, first-out method or lower of cost or net realizable value using the average cost or first-in, first-out method. The majority of all other inventories are valued at the lower of cost or net realizable value using the average cost method.

Earnings per share (Policies)

Earnings per share (Policies)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Earnings per share	Basic earnings per share is computed by dividing net income by the weighted average number of shares of common stock outstanding during the applicable period. Diluted earnings per share is computed by dividing net income by the total of the weighted average number of shares of common stock outstanding during the applicable period, plus the effect of non-vested performance share awards and restricted stock units. Common stock outstanding includes issued shares less shares held in treasury.

Revenue from contracts with c_2

Revenue from contracts with customers (Policies)	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Revenue from contracts with customers	Revenue is recognized when a performance obligation is satisfied by transferring control over a product or service to a customer. Revenue is measured based on consideration specified in a contract with a customer and excludes any sales incentives and amounts collected on behalf of third parties. The Company is considered an agent for certain taxes collected from customers. As such, the Company presents revenues net of these taxes at the time of sale to be remitted to governmental authorities, including sales and use taxes.

Business Combinations (Policies

Business Combinations (Policies)	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Business Combinations Policy [Policy Text Block]	The following acquisitions were accounted for as business combinations in accordance with ASC 805 - Business Combinations. The results of the acquired businesses have been included in the Consolidated Financial Statements beginning on the acquisition date. Pro forma financial amounts reflecting the effects of the business combinations are not presented, as none of these business combinations, individually or in the aggregate, were material to the Company's financial position or results of operations.

Fair value disclosures (Policie

Fair value disclosures (Policies)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair value measurements	The Company measures its investments in certain fixed-income and equity securities at fair value with changes in fair value recognized in income.
Investments	The Company did not elect the fair value option, which records gains and losses in income, for its available-for-sale securities, which include mortgage-backed securities and U.S. Treasury securities. These available-for-sale securities are recorded at fair value and are classified as investments on the Consolidated Balance Sheets.

Business segment data (Policies

Business segment data (Policies)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Business segment data	The Company's reportable segments are those that are based on the Company's method of internal reporting, which generally segregates the strategic business units due to differences in products, services and regulation. The internal reporting of these operating segments is defined based on the reporting and review process used by the Company's chief executive officer.

Contingencies (Policies)

Contingencies (Policies)	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Contingencies	The Company is party to claims and lawsuits arising out of its business and that of its consolidated subsidiaries, which may include, but are not limited to, matters involving property damage, personal injury, and environmental, contractual, statutory and regulatory obligations. The Company accrues a liability for those contingencies when the incurrence of a loss is probable and the amount can be reasonably estimated. If a range of amounts can be reasonably estimated and no amount within the range is a better estimate than any other amount, then the minimum of the range is accrued. The Company does not accrue liabilities when the likelihood that the liability has been incurred is probable but the amount cannot be reasonably estimated or when the liability is believed to be only reasonably possible or remote. For contingencies where an unfavorable outcome is probable or reasonably possible and which are material, the Company discloses the nature of the contingency and, in some circumstances, an estimate of the possible loss. Accruals are based on the best information available, but in certain situations management is unable to estimate an amount or range of a reasonably possible loss including, but not limited to when: (1) the damages are unsubstantiated or indeterminate, (2) the proceedings are in the early stages, (3) numerous parties are involved, or (4) the matter involves novel or unsettled legal theories.
Variable interest entity	The Company evaluates its arrangements and contracts with other entities to determine if they are VIEs and if so, if the Company is the primary beneficiary.

Accounts receivable and allowan

Accounts receivable and allowance for doubtful accounts Receivables and allowance for expected credit losses (Tables)	3 Months Ended
	Mar. 31, 2021
Credit Loss [Abstract]
Accounts Receivable, Allowance for Credit Loss [Table Text Block]	Details of the Company's expected credit losses were as follows: Electric Natural gas Pipeline Construction Construction Total (In thousands) At December 31, 2020 $ 899 $ 2,571 $ 2 $ 6,164 $ 5,722 $ 15,358 Current expected credit loss provision 538 1,273 — (1,049) (1,079) (317) Less write-offs charged against the allowance 888 1,107 — 273 401 2,669 Credit loss recoveries collected 129 213 — — — 342 At March 31, 2021 $ 678 $ 2,950 $ 2 $ 4,842 $ 4,242 $ 12,714 Electric Natural gas Pipeline Construction Construction Total (In thousands) At January 1, 2020 $ 328 $ 1,056 $ — $ 5,357 $ 1,756 $ 8,497 Current expected credit loss provision 555 1,156 — 694 1,150 3,555 Less write-offs charged against the allowance 500 624 — 68 73 1,265 Credit loss recoveries collected 109 229 — — — 338 At March 31, 2020 $ 492 $ 1,817 $ — $ 5,983 $ 2,833 $ 11,125

Inventories and natural gas i_3

Inventories and natural gas in storage (Tables)	3 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Inventories	Inventories on the Consolidated Balance Sheets were as follows: March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Aggregates held for resale $ 180,450 $ 155,976 $ 175,782 Asphalt oil 59,853 73,842 28,238 Materials and supplies 26,481 26,293 25,142 Merchandise for resale 24,319 23,109 21,087 Natural gas in storage (current) 8,113 7,872 21,919 Other 17,521 18,866 18,999 Total $ 316,737 $ 305,958 $ 291,167

Earnings per share (Tables)

Earnings per share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Weighted average common shares outstanding	A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings per share calculations follows: Three Months Ended March 31, 2021 2020 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 200,708 200,440 Effect of dilutive performance share awards and restricted stock units 244 16 Weighted average common shares outstanding - diluted 200,952 200,456 Shares excluded from the calculation of diluted earnings per share — 68 Dividends declared per common share $ .2125 $ .2075

Accumulated other comprehensi_2

Accumulated other comprehensive income (loss) (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Accumulated comprehensive loss	The after-tax changes in the components of accumulated other comprehensive loss were as follows: Net Unrealized Postretirement Net Unrealized Total (In thousands) At December 31, 2020 $ (984) $ (47,207) $ 113 $ (48,078) Other comprehensive loss before reclassifications — — (44) (44) Amounts reclassified from accumulated other comprehensive loss 111 466 35 612 Net current-period other comprehensive income (loss) 111 466 (9) 568 At March 31, 2021 $ (873) $ (46,741) $ 104 $ (47,510) Net Unrealized Postretirement Net Unrealized Total (In thousands) At December 31, 2019 $ (1,430) $ (40,734) $ 62 $ (42,102) Other comprehensive income before reclassifications — — 135 135 Amounts reclassified (to) from accumulated other comprehensive loss 111 462 (1) 572 Net current-period other comprehensive income 111 462 134 707 At March 31, 2020 $ (1,319) $ (40,272) $ 196 $ (41,395)
Reclassification out of accumulated other comprehensive loss	The following amounts were reclassified out of accumulated other comprehensive loss into net income. The amounts presented in parenthesis indicate a decrease to net income on the Consolidated Statements of Income. The reclassifications were as follows: Three Months Ended Location on Consolidated March 31, 2021 2020 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ (148) $ (147) Interest expense 37 36 Income taxes (111) (111) Amortization of postretirement liability losses included in net periodic benefit cost (617) (611) Other income 151 149 Income taxes (466) (462) Reclassification adjustment on available-for-sale investments included in net income (44) 1 Other income 9 — Income taxes (35) 1 Total reclassifications $ (612) $ (572)

Revenue from contracts with c_3

Revenue from contracts with customers (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Disaggregation of revenue	In the following tables, revenue is disaggregated by the type of customer or service provided. The Company believes this level of disaggregation best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The table also includes a reconciliation of the disaggregated revenue by reportable segments. For more information on the Company's business segments, see Note 17. Three Months Ended March 31, 2021 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 33,436 $ 203,137 $ — $ — $ — $ — $ 236,573 Commercial utility sales 32,928 120,052 — — — — 152,980 Industrial utility sales 10,029 8,812 — — — — 18,841 Other utility sales 1,566 — — — — — 1,566 Natural gas transportation — 12,452 29,417 — — — 41,869 Natural gas storage — — 4,029 — — — 4,029 Contracting services — — — 96,025 — — 96,025 Construction materials — — — 216,412 — — 216,412 Intrasegment eliminations — — — (46,716) — — (46,716) Inside specialty contracting — — — — 355,190 — 355,190 Outside specialty contracting — — — — 151,363 — 151,363 Other 9,773 3,009 2,660 — 36 3,341 18,819 Intersegment eliminations (136) (142) (26,229) (62) (1,042) (3,324) (30,935) Revenues from contracts with customers 87,596 347,320 9,877 265,659 505,547 17 1,216,016 Revenues out of scope (2,923) 2,886 36 — 11,923 — 11,922 Total external operating revenues $ 84,673 $ 350,206 $ 9,913 $ 265,659 $ 517,470 $ 17 $ 1,227,938 Three Months Ended March 31, 2020 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 32,349 $ 186,701 $ — $ — $ — $ — $ 219,050 Commercial utility sales 33,587 114,996 — — — — 148,583 Industrial utility sales 10,367 8,521 — — — — 18,888 Other utility sales 1,648 — — — — — 1,648 Natural gas transportation — 11,798 27,432 — — — 39,230 Natural gas gathering — — 2,090 — — — 2,090 Natural gas storage — — 3,046 — — — 3,046 Contracting services — — — 98,401 — — 98,401 Construction materials — — — 207,910 — — 207,910 Intrasegment eliminations — — — (44,104) — — (44,104) Inside specialty contracting — — — — 372,209 — 372,209 Outside specialty contracting — — — — 130,150 — 130,150 Other 8,450 2,498 3,241 — 351 2,991 17,531 Intersegment eliminations (195) (185) (25,199) (63) (2,470) (2,973) (31,085) Revenues from contracts with customers 86,206 324,329 10,610 262,144 500,240 18 1,183,547 Revenues out of scope (298) 2,114 45 — 11,965 — 13,826 Total external operating revenues $ 85,908 $ 326,443 $ 10,655 $ 262,144 $ 512,205 $ 18 $ 1,197,373
Contract balances	The changes in contract assets and liabilities were as follows: March 31, 2021 December 31, 2020 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 107,543 $ 104,345 $ 3,198 Receivables, net Contract liabilities - current (142,828) (158,603) 15,775 Accounts payable Contract liabilities - noncurrent (171) (52) (119) Noncurrent liabilities - other Net contract liabilities $ (35,456) $ (54,310) $ 18,854

Goodwill and other intangible_2

Goodwill and other intangible assets (Tables)	3 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the carrying amount of goodwill	The changes in the carrying amount of goodwill were as follows: Balance at January 1, 2021 Goodwill Measurement Balance at March 31, 2021 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 226,003 — — 226,003 Construction services 143,224 — — 143,224 Total $ 714,963 $ — $ — $ 714,963 Balance at January 1, 2020 Goodwill Measurement Balance at March 31, 2020 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 217,234 6,483 — 223,717 Construction services 118,388 25,686 — 144,074 Total $ 681,358 $ 32,169 $ — $ 713,527 Balance at January 1, 2020 Goodwill Measurement Balance at December 31, 2020 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 217,234 8,778 (9) 226,003 Construction services 118,388 24,436 400 143,224 Total $ 681,358 $ 33,214 $ 391 $ 714,963
Other amortizable intangible assets	Other amortizable intangible assets were as follows: March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Customer relationships $ 28,836 $ 30,087 $ 28,836 Less accumulated amortization 7,792 4,138 6,887 21,044 25,949 21,949 Noncompete agreements 3,941 4,229 3,941 Less accumulated amortization 2,441 1,928 2,309 1,500 2,301 1,632 Other 11,957 13,060 12,927 Less accumulated amortization 10,540 7,060 11,012 1,417 6,000 1,915 Total $ 23,961 $ 34,250 $ 25,496
Estimated amortization expense	Estimated amortization expense for identifiable intangible assets as of March 31, 2021, was: Remainder of 2021 2022 2023 2024 2025 Thereafter (In thousands) Amortization expense $ 3,377 $ 4,394 $ 4,121 $ 3,799 $ 1,862 $ 6,408

Regulatory assets and liabili_2

Regulatory assets and liabilities (Tables)	3 Months Ended
	Mar. 31, 2021
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	The following table summarizes the individual components of unamortized regulatory assets and liabilities: Estimated Recovery or Refund Period as of March 31, 2021 * March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 76,782 $ 39,805 $ 42,481 Cost recovery mechanisms Up to 1 year 7,130 6,686 10,645 Conservation programs Up to 1 year 6,679 6,303 7,117 Other Up to 1 year 7,861 2,412 8,284 98,452 55,206 68,527 Noncurrent: Pension and postretirement benefits ** 155,924 157,051 155,942 Plant retirement - 73,498 41,080 65,919 Plant costs/asset retirement obligations Over plant lives 72,250 67,475 71,740 Manufactured gas plant site remediation - 26,002 15,699 26,429 Cost recovery mechanisms Up to 10 years 15,508 11,891 16,245 Natural gas costs recoverable through rate adjustments Up to 3 years 15,158 33,027 21,539 Taxes recoverable from customers Over plant lives 10,800 11,082 10,785 Long-term debt refinancing costs Up to 39 years 4,268 4,133 4,426 Other Up to 18 years 6,509 6,751 6,356 379,917 348,189 379,381 Total regulatory assets $ 478,369 $ 403,395 $ 447,908 Regulatory liabilities: Current: Natural gas costs refundable through rate adjustments Up to 1 year $ 16,344 $ 32,181 $ 18,565 Taxes refundable to customers Up to 1 year 3,092 4,002 3,557 Electric fuel and purchased power deferral Up to 1 year 2,001 7,188 3,667 Other Up to 1 year 12,829 16,701 5,661 34,266 60,072 31,450 Noncurrent: Taxes refundable to customers Over plant lives 224,795 240,148 227,850 Plant removal and decommissioning costs Over plant lives 169,430 174,120 167,171 Pension and postretirement benefits ** 16,965 18,040 16,989 Other Up to 21 years 17,870 10,897 16,065 429,060 443,205 428,075 Total regulatory liabilities $ 463,326 $ 503,277 $ 459,525 Net regulatory position $ 15,043 $ (99,882) $ (11,617) * Estimated recovery or refund period for amounts currently being recovered or refunded in rates charged to customers. ** Recovered as expense is incurred or cash contributions are made.
Regulatory Liabilities	The following table summarizes the individual components of unamortized regulatory assets and liabilities: Estimated Recovery or Refund Period as of March 31, 2021 * March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 76,782 $ 39,805 $ 42,481 Cost recovery mechanisms Up to 1 year 7,130 6,686 10,645 Conservation programs Up to 1 year 6,679 6,303 7,117 Other Up to 1 year 7,861 2,412 8,284 98,452 55,206 68,527 Noncurrent: Pension and postretirement benefits ** 155,924 157,051 155,942 Plant retirement - 73,498 41,080 65,919 Plant costs/asset retirement obligations Over plant lives 72,250 67,475 71,740 Manufactured gas plant site remediation - 26,002 15,699 26,429 Cost recovery mechanisms Up to 10 years 15,508 11,891 16,245 Natural gas costs recoverable through rate adjustments Up to 3 years 15,158 33,027 21,539 Taxes recoverable from customers Over plant lives 10,800 11,082 10,785 Long-term debt refinancing costs Up to 39 years 4,268 4,133 4,426 Other Up to 18 years 6,509 6,751 6,356 379,917 348,189 379,381 Total regulatory assets $ 478,369 $ 403,395 $ 447,908 Regulatory liabilities: Current: Natural gas costs refundable through rate adjustments Up to 1 year $ 16,344 $ 32,181 $ 18,565 Taxes refundable to customers Up to 1 year 3,092 4,002 3,557 Electric fuel and purchased power deferral Up to 1 year 2,001 7,188 3,667 Other Up to 1 year 12,829 16,701 5,661 34,266 60,072 31,450 Noncurrent: Taxes refundable to customers Over plant lives 224,795 240,148 227,850 Plant removal and decommissioning costs Over plant lives 169,430 174,120 167,171 Pension and postretirement benefits ** 16,965 18,040 16,989 Other Up to 21 years 17,870 10,897 16,065 429,060 443,205 428,075 Total regulatory liabilities $ 463,326 $ 503,277 $ 459,525 Net regulatory position $ 15,043 $ (99,882) $ (11,617) * Estimated recovery or refund period for amounts currently being recovered or refunded in rates charged to customers. ** Recovered as expense is incurred or cash contributions are made.

Fair value measurements (Tables

Fair value measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Available-for-sale securities	Details of available-for-sale securities were as follows: March 31, 2021 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 8,709 $ 155 $ 10 $ 8,854 U.S. Treasury securities 2,636 — 14 2,622 Total $ 11,345 $ 155 $ 24 $ 11,476 March 31, 2020 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,691 $ 236 $ — $ 9,927 U.S. Treasury securities 1,173 12 — 1,185 Total $ 10,864 $ 248 $ — $ 11,112 December 31, 2020 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,799 $ 156 $ 9 $ 9,946 U.S. Treasury securities 1,386 — 5 1,381 Total $ 11,185 $ 156 $ 14 $ 11,327
Assets and liabilities measured at fair value on a recurring basis	The Company's assets measured at fair value on a recurring basis were as follows: Fair Value Measurements at March 31, 2021, Using Quoted Prices in Significant Significant Balance at March 31, 2021 (In thousands) Assets: Money market funds $ 9,388 $ — $ 9,388 Insurance contracts* — 101,632 101,632 Available-for-sale securities: Mortgage-backed securities — 8,854 — 8,854 U.S. Treasury securities — 2,622 — 2,622 Total assets measured at fair value $ — $ 122,496 $ — $ 122,496 * The insurance contracts invest approximately 54 percent in fixed-income investments, 19 percent in common stock of large-cap companies, 10 percent in common stock of mid-cap companies, 9 percent in common stock of small-cap companies, 6 percent in target date investments and 2 percent in cash equivalents. Fair Value Measurements at March 31, 2020, Using Quoted Prices in Significant Significant Balance at March 31, 2020 (In thousands) Assets: Money market funds $ — $ 8,470 $ — $ 8,470 Insurance contract* — 83,254 — 83,254 Available-for-sale securities: Mortgage-backed securities — 9,927 — 9,927 U.S. Treasury securities — 1,185 — 1,185 Total assets measured at fair value $ — $ 102,836 $ — $ 102,836 * The insurance contract invests approximately 58 percent in fixed-income investments, 20 percent in common stock of large-cap companies, 8 percent in common stock of mid-cap companies, 8 percent in common stock of small-cap companies, 4 percent in target date investments and 2 percent in cash equivalents. Fair Value Measurements at December 31, 2020, Using Quoted Prices in Significant Significant Balance at December 31, 2020 (In thousands) Assets: Money market funds $ — $ 8,917 $ — $ 8,917 Insurance contract* — 100,104 — 100,104 Available-for-sale securities: Mortgage-backed securities — 9,946 — 9,946 U.S. Treasury securities — 1,381 — 1,381 Total assets measured at fair value $ — $ 120,348 $ — $ 120,348 * The insurance contract invests approximately 57 percent in fixed-income investments, 18 percent in common stock of large-cap companies, 9 percent in common stock of mid-cap companies, 9 percent in common stock of small-cap companies, 5 percent in target date investments and 2 percent in cash equivalents.
Fair value of long term debt outstanding	The estimated fair value of the Company's Level 2 long-term debt was as follows: March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Carrying amount $ 2,253,274 $ 2,455,235 $ 2,213,130 Fair value $ 2,473,806 $ 2,618,297 $ 2,537,289

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Long-term debt outstanding	Long-term debt outstanding was as follows: Weighted Average Interest Rate at March 31, 2021 March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Senior Notes due on dates ranging from October 22, 2022 to October 30, 2060 4.40 % $ 1,950,000 $ 1,850,000 $ 1,950,000 Commercial paper supported by revolving credit agreements .33 % 218,900 265,000 125,600 Credit agreements due on June 7, 2024 2.20 % 43,350 259,550 95,900 Medium-Term Notes due on dates ranging from September 15, 2027 to March 16, 2029 7.32 % 35,000 50,000 35,000 Term Loan Agreement due on September 3, 2032 2.00 % 8,400 9,100 8,400 Other notes due on dates ranging from July 15, 2021 to July 1, 2061 .82 % 3,282 28,374 4,034 Less unamortized debt issuance costs 5,655 6,640 5,803 Less discount 3 149 1 Total long-term debt 2,253,274 2,455,235 2,213,130 Less current maturities 1,552 16,560 1,555 Net long-term debt $ 2,251,722 $ 2,438,675 $ 2,211,575
Schedule of debt maturities	Long-term debt maturities, which excludes unamortized debt issuance costs and discount, at March 31, 2021, were as follows: Remainder of 2022 2023 2024 2025 Thereafter (In thousands) Long-term debt maturities $ 780 $ 148,021 $ 77,921 $ 323,672 $ 177,802 $ 1,530,736

Cash flow information (Tables)

Cash flow information (Tables)	3 Months Ended
	Mar. 31, 2021
Supplemental Cash Flow Information [Abstract]
Cash expenditures for interest and income taxes and noncash investing and financing transactions	Cash expenditures for interest and income taxes were as follows: Three Months Ended March 31, 2021 2020 (In thousands) Interest, net* $ 14,303 $ 15,978 Income taxes paid (refunded), net $ 13,880 $ (1) * AFUDC - borrowed was $348,000 and $627,000 for the three months ended March 31, 2021 and 2020, respectively. Noncash investing and financing transactions were as follows: March 31, 2021 March 31, 2020 December 31, 2020 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 9,236 $ 10,655 $ 54,356 Property, plant and equipment additions in accounts payable $ 20,594 $ 27,425 $ 26,082 Accrual for holdback payment related to a business combination $ — $ 5,000 $ 2,500

Business segment data (Tables)

Business segment data (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Information on the Company's businesses	Information on the Company's segments was as follows: Three Months Ended March 31, 2021 2020 (In thousands) External operating revenues: Regulated operations: Electric $ 84,673 $ 85,908 Natural gas distribution 350,206 326,443 Pipeline 7,502 6,331 442,381 418,682 Non-regulated operations: Pipeline 2,411 4,324 Construction materials and contracting 265,659 262,144 Construction services 517,470 512,205 Other 17 18 785,557 778,691 Total external operating revenues $ 1,227,938 $ 1,197,373 Three Months Ended March 31, 2021 2020 (In thousands) Intersegment operating revenues: Regulated operations: Electric $ 136 $ 195 Natural gas distribution 142 185 Pipeline 25,990 25,183 26,268 25,563 Non-regulated operations: Pipeline 239 16 Construction materials and contracting 62 63 Construction services 1,042 2,470 Other 3,324 2,973 4,667 5,522 Intersegment eliminations (30,935) (31,085) Total intersegment operating revenues $ — $ — Operating income (loss): Electric $ 13,865 $ 14,859 Natural gas distribution 53,573 49,998 Pipeline 12,536 11,419 Construction materials and contracting (34,889) (43,269) Construction services 40,277 23,796 Other (198) 267 Total operating income $ 85,164 $ 57,070 Net income (loss): Regulated operations: Electric $ 10,749 $ 11,374 Natural gas distribution 36,178 32,369 Pipeline 9,194 7,386 56,121 51,129 Non-regulated operations: Pipeline (296) (13) Construction materials and contracting (30,813) (38,215) Construction services 29,825 16,823 Other (2,721) (4,185) (4,005) (25,590) Income from continuing operations 52,116 25,539 Income (loss) from discontinued operations, net of tax 15 (409) Net income $ 52,131 $ 25,130

Employee benefit plans (Tables)

Employee benefit plans (Tables)	3 Months Ended
	Mar. 31, 2021
Retirement Benefits [Abstract]
Schedule of net benefit costs	Components of net periodic benefit cost (credit) for the Company's pension and other postretirement benefit plans were as follows: Pension Benefits Other Three Months Ended March 31, 2021 2020 2021 2020 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 400 $ 352 Interest cost 2,455 2,973 466 591 Expected return on assets (4,894) (4,761) (1,275) (1,248) Amortization of prior service credit — — (349) (297) Amortization of net actuarial loss 2,004 1,863 6 2 Net periodic benefit cost (credit), including amount capitalized (435) 75 (752) (600) Less amount capitalized — — 39 32 Net periodic benefit cost (credit) $ (435) $ 75 $ (791) $ (632)

Receivables and allowance for_3

Receivables and allowance for expected credit losses (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Credit Loss [Abstract]
Accounts Receivable, Noncurrent, 90 Days or More Past Due, Still Accruing	$ 33.9	$ 43.9	$ 51.8

Accounts receivable and allow_2

Accounts receivable and allowance for doubtful accounts Receivables and allowance for expected credit losses (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	$ 15,358	$ 8,497
Current expected credit loss provision	(317)	3,555
Less write-offs charged against the allowance	2,669	1,265
Credit loss recoveries collected	342	338
Balance	12,714	11,125
Electric
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	899	328
Current expected credit loss provision	538	555
Less write-offs charged against the allowance	888	500
Credit loss recoveries collected	129	109
Balance	678	492
Natural gas distribution
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	2,571	1,056
Current expected credit loss provision	1,273	1,156
Less write-offs charged against the allowance	1,107	624
Credit loss recoveries collected	213	229
Balance	2,950	1,817
Pipeline
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	2	0
Current expected credit loss provision	0	0
Less write-offs charged against the allowance	0	0
Credit loss recoveries collected	0	0
Balance	2	0
Construction materials and contracting
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	6,164	5,357
Current expected credit loss provision	(1,049)	694
Less write-offs charged against the allowance	273	68
Credit loss recoveries collected	0	0
Balance	4,842	5,983
Construction services
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	5,722	1,756
Current expected credit loss provision	(1,079)	1,150
Less write-offs charged against the allowance	401	73
Credit loss recoveries collected	0	0
Balance	$ 4,242	$ 2,833

Inventories and natural gas i_4

Inventories and natural gas in storage (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Inventory Disclosure [Abstract]
Aggregates held for resale	$ 180,450	$ 175,782	$ 155,976
Asphalt oil	59,853	28,238	73,842
Materials and supplies	26,481	25,142	26,293
Merchandise for resale	24,319	21,087	23,109
Natural gas in storage (current)	8,113	21,919	7,872
Other	17,521	18,999	18,866
Total	316,737	291,167	305,958
Natural gas in storage noncurrent	$ 47,500	$ 47,500	$ 48,300

Earnings per share (Details)

Earnings per share (Details) - $ / shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	200,708	200,440
Effect of dilutive performance share awards and restricted stock units	244	16
Weighted average common shares outstanding - diluted	200,952	200,456
Shares excluded from the calculation of diluted earnings per share	0	68
Dividends declared per common share	$ 0.2125	$ 0.2075

Equity (Details)

Equity (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Class of Stock [Line Items]
Common Stock, Shares Authorized	500,000,000	500,000,000	500,000,000
Common Stock, Shares, Issued	201,733,458	201,061,198	201,061,198
Proceeds from issuance of common stock	$ 19,699,000	$ 3,410,000
At-the-market offering
Class of Stock [Line Items]
Common Stock, Shares Authorized	6,400,000
Common Stock, Shares, Issued	672,260	0
Proceeds from issuance of common stock	$ 19,700,000
Issuance costs from Issuance of Common Stock through the ATM Program	$ 300,000
Common Stock, Capital Shares Reserved for Future Issuance	5,700,000

Accumulated other comprehensi_3

Accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	$ 3,079,105	$ 2,847,246
Other comprehensive income (loss)	568	707
Balance	3,100,306	2,836,592
Net unrealized gain (loss) on derivative instruments qualifying as hedges
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(984)	(1,430)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified (to) from accumulated other comprehensive loss	111	111
Other comprehensive income (loss)	111	111
Balance	(873)	(1,319)
Postretirement liability adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(47,207)	(40,734)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified (to) from accumulated other comprehensive loss	466	462
Other comprehensive income (loss)	466	462
Balance	(46,741)	(40,272)
Net unrealized gain (loss) on available-for-sale investments
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	113	62
Other comprehensive income (loss) before reclassifications	(44)	135
Amounts reclassified (to) from accumulated other comprehensive loss	35	(1)
Other comprehensive income (loss)	(9)	134
Balance	104	196
Total accumulated other comprehensive loss
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(48,078)	(42,102)
Other comprehensive income (loss) before reclassifications	(44)	135
Amounts reclassified (to) from accumulated other comprehensive loss	612	572
Other comprehensive income (loss)	568	707
Balance	$ (47,510)	$ (41,395)

Reclassification out of accumul

Reclassification out of accumulated other comprehensive loss (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Interest expense	$ (23,453)	$ (24,553)
Income taxes	(12,949)	(5,973)
Other income	3,354	(1,005)
Net Income	52,131	25,130
Reclassification out of accumulated other comprehensive loss
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Net Income	(612)	(572)
Reclassification adjustment for loss on derivative instruments included in net income | Reclassification out of accumulated other comprehensive loss | Interest rate contract
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Interest expense	(148)	(147)
Income taxes	37	36
Net Income	(111)	(111)
Amortization of postretirement liability losses included in net periodic benefit cost | Reclassification out of accumulated other comprehensive loss
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Income taxes	151	149
Other income	(617)	(611)
Net Income	(466)	(462)
Reclassification adjustment on available-for-sale investments included in net income | Reclassification out of accumulated other comprehensive loss
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Income taxes	9	0
Other income	(44)	1
Net Income	$ (35)	$ 1

Disaggregation of revenue (Deta

Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Operating revenues:	$ 1,227,938	$ 1,197,373
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(30,935)	(31,085)
Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(46,716)	(44,104)
Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	41,869	39,230
Natural gas gathering
Disaggregation of Revenue [Line Items]
Operating revenues:		2,090
Natural gas storage
Disaggregation of Revenue [Line Items]
Operating revenues:	4,029	3,046
Contracting services
Disaggregation of Revenue [Line Items]
Operating revenues:	96,025	98,401
Construction materials
Disaggregation of Revenue [Line Items]
Operating revenues:	216,412	207,910
Inside specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	355,190	372,209
Outside specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	151,363	130,150
Other
Disaggregation of Revenue [Line Items]
Operating revenues:	18,819	17,531
Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	1,216,016	1,183,547
Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	11,922	13,826
Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	236,573	219,050
Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	152,980	148,583
Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	18,841	18,888
Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	1,566	1,648
Electric
Disaggregation of Revenue [Line Items]
Operating revenues:	84,673	85,908
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(136)	(195)
Electric | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	9,773	8,450
Electric | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	87,596	86,206
Electric | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	(2,923)	(298)
Electric | Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	33,436	32,349
Electric | Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	32,928	33,587
Electric | Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	10,029	10,367
Electric | Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	1,566	1,648
Natural gas distribution
Disaggregation of Revenue [Line Items]
Operating revenues:	350,206	326,443
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(142)	(185)
Natural gas distribution | Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	12,452	11,798
Natural gas distribution | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	3,009	2,498
Natural gas distribution | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	347,320	324,329
Natural gas distribution | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	2,886	2,114
Natural gas distribution | Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	203,137	186,701
Natural gas distribution | Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	120,052	114,996
Natural gas distribution | Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	8,812	8,521
Natural gas distribution | Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0
Pipeline
Disaggregation of Revenue [Line Items]
Operating revenues:	9,913	10,655
Pipeline | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(26,229)	(25,199)
Pipeline | Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	29,417	27,432
Pipeline | Natural gas gathering
Disaggregation of Revenue [Line Items]
Operating revenues:		2,090
Pipeline | Natural gas storage
Disaggregation of Revenue [Line Items]
Operating revenues:	4,029	3,046
Pipeline | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	2,660	3,241
Pipeline | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	9,877	10,610
Pipeline | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	36	45
Construction materials and contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	265,659	262,144
Construction materials and contracting | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(62)	(63)
Construction materials and contracting | Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(46,716)	(44,104)
Construction materials and contracting | Contracting services
Disaggregation of Revenue [Line Items]
Operating revenues:	96,025	98,401
Construction materials and contracting | Construction materials
Disaggregation of Revenue [Line Items]
Operating revenues:	216,412	207,910
Construction materials and contracting | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0
Construction materials and contracting | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	265,659	262,144
Construction materials and contracting | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0
Construction services
Disaggregation of Revenue [Line Items]
Operating revenues:	517,470	512,205
Construction services | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(1,042)	(2,470)
Construction services | Inside specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	355,190	372,209
Construction services | Outside specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	151,363	130,150
Construction services | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	36	351
Construction services | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	505,547	500,240
Construction services | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	11,923	11,965
Other
Disaggregation of Revenue [Line Items]
Operating revenues:	17	18
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(3,324)	(2,973)
Other | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	3,341	2,991
Other | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	17	18
Other | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	$ 0	$ 0

Contract balances (Details 2)

Contract balances (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Contract assets	$ 107,543		$ 104,345
Change in contract assets	3,198
Contract liabilities - current	(142,828)		(158,603)
Change in contract liabilities - current	15,775
Contract liabilities - noncurrent	(171)		(52)
Change in contract liabilities - noncurrent	(119)
Net contract liabilities	(35,456)		$ (54,310)
Change in net contract liabilities	18,854
Amounts included in contract liability at the beginning of the period	123,400	$ 89,400
Amounts from performance obligations satisfied in prior periods	$ 34,300	$ 19,500

Revenue from contracts with c_4

Revenue from contracts with customers Remaining performance obligations (Details 3) $ in Millions	Mar. 31, 2021USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 2,200
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 1,700
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 283.8
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	13 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 213.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	25 months

Business Combinations (Details)

Business Combinations (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill	$ 714,963,000	$ 714,963,000	$ 713,527,000	$ 681,358,000
2020 Acquisition
Business Acquisition [Line Items]
Gross Aggregate Consideration	110,200,000
Cash Assumed	1,700,000
Business Combination, Consideration Transferred	106,000,000
Business Combination indemnity holdback liability	2,500,000
Current Assets	54,800,000
Property, Plant, and Equipment	27,100,000
Goodwill	33,600,000
Other Intangibles	19,000,000
Current Liabilities	22,600,000
Deferred Credits and Other Liabilities	300,000
Asset Retirement Obligation	$ 1,400,000

Lessor accounting (Details)

Lessor accounting (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Operating Lease, Lease Income	$ 12	$ 12.1
Lessor, Operating Lease, Payments to be Received, Next Twelve Months	$ 10.4

Goodwill rollforward (Details)

Goodwill rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Goodwill [Roll Forward]
Balance at beginning of period	$ 714,963	$ 681,358	$ 681,358
Goodwill acquired during the year	0	32,169	33,214
Measurement period adjustments	0	0	391
Balance at end of period	714,963	713,527	714,963
Natural gas distribution
Goodwill [Roll Forward]
Balance at beginning of period	345,736	345,736	345,736
Goodwill acquired during the year	0	0	0
Measurement period adjustments	0	0	0
Balance at end of period	345,736	345,736	345,736
Construction materials and contracting
Goodwill [Roll Forward]
Balance at beginning of period	226,003	217,234	217,234
Goodwill acquired during the year	0	6,483	8,778
Measurement period adjustments	0	0	(9)
Balance at end of period	226,003	223,717	226,003
Construction services
Goodwill [Roll Forward]
Balance at beginning of period	143,224	118,388	118,388
Goodwill acquired during the year	0	25,686	24,436
Measurement period adjustments	0	0	400
Balance at end of period	$ 143,224	$ 144,074	$ 143,224

Other intangible assets (Detail

Other intangible assets (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 23,961	$ 34,250	$ 25,496
Amortization of intangible assets	1,500	2,000
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	28,836	30,087	28,836
Intangible assets, less accumulated amortization	7,792	4,138	6,887
Intangible assets, net (excluding goodwill)	21,044	25,949	21,949
Noncompete agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	3,941	4,229	3,941
Intangible assets, less accumulated amortization	2,441	1,928	2,309
Intangible assets, net (excluding goodwill)	1,500	2,301	1,632
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	11,957	13,060	12,927
Intangible assets, less accumulated amortization	10,540	7,060	11,012
Intangible assets, net (excluding goodwill)	$ 1,417	$ 6,000	$ 1,915

Future amortization expense (De

Future amortization expense (Details 3) $ in Thousands	Mar. 31, 2021USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Remainder of 2021	$ 3,377
2022	4,394
2023	4,121
2024	3,799
2025	1,862
Thereafter	$ 6,408

Regulatory assets and liabili_3

Regulatory assets and liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Feb. 28, 2021	Dec. 31, 2020	Mar. 31, 2020
Regulatory Assets and Liabilities
Regulatory Assets, Current	$ 98,452		$ 68,527	$ 55,206
Regulatory Assets, Noncurrent	379,917		379,381	348,189
Total regulatory assets	478,369		447,908	403,395
Regulatory Liability, Current	34,266		31,450	60,072
Regulatory Liability, Noncurrent	429,060		428,075	443,205
Total regulatory liabilities	463,326		459,525	503,277
Net regulatory position	15,043		(11,617)	(99,882)
Regulatory assets not earning a rate of return	$ 361,400		332,500	285,800
Natural gas costs refundable through rate adjustments
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 1 year
Regulatory Liability, Current	$ 16,344		18,565	32,181
Taxes refundable to customers
Regulatory Assets and Liabilities
Regulatory Liability, Current	3,092		3,557	4,002
Regulatory Liability, Noncurrent	$ 224,795		227,850	240,148
Taxes refundable to customers | Minimum [Member]
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 1 year
Taxes refundable to customers | Maximum [Member]
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Over plant lives
Electric fuel and purchased power deferral
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 1 year
Regulatory Liability, Current	$ 2,001		3,667	7,188
Plant removal and decommissioning costs
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Over plant lives
Regulatory Liability, Noncurrent	$ 169,430		167,171	174,120
Pension and postretirement benefits
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	**
Regulatory Liability, Noncurrent	$ 16,965		16,989	18,040
Other Regulatory Liabilities
Regulatory Assets and Liabilities
Regulatory Liability, Current	12,829		5,661	16,701
Regulatory Liability, Noncurrent	$ 17,870		16,065	10,897
Other Regulatory Liabilities | Minimum [Member]
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 1 year
Other Regulatory Liabilities | Maximum [Member]
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 21 years
Natural gas costs recoverable through rate adjustments
Regulatory Assets and Liabilities
Regulatory Assets, Current	$ 76,782		42,481	39,805
Regulatory Assets, Noncurrent	$ 15,158		21,539	33,027
Natural gas costs recoverable through rate adjustments | Minimum [Member]
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 1 year
Natural gas costs recoverable through rate adjustments | Maximum [Member]
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 3 years
Cost recovery mechanisms
Regulatory Assets and Liabilities
Regulatory Assets, Current	$ 7,130		10,645	6,686
Regulatory Assets, Noncurrent	$ 15,508		16,245	11,891
Cost recovery mechanisms | Minimum [Member]
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 1 year
Cost recovery mechanisms | Maximum [Member]
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 10 years
Conservation programs
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 1 year
Regulatory Assets, Current	$ 6,679		7,117	6,303
Pension and postretirement benefits
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	**
Regulatory Assets, Noncurrent	$ 155,924		155,942	157,051
Plant removal and decommissioning costs
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	-
Regulatory Assets, Noncurrent	$ 73,498		65,919	41,080
Plant costs/asset retirement obligations
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Over plant lives
Regulatory Assets, Noncurrent	$ 72,250		71,740	67,475
Manufactured gas plant site remediation
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	-
Regulatory Assets, Noncurrent	$ 26,002		26,429	15,699
Taxes refundable to customers
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Over plant lives
Regulatory Assets, Noncurrent	$ 10,800		10,785	11,082
Long-term debt refinancing costs
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 39 years
Regulatory Assets, Noncurrent	$ 4,268		4,426	4,133
Other Regulatory Liabilities
Regulatory Assets and Liabilities
Regulatory Assets, Current	7,861		8,284	2,412
Regulatory Assets, Noncurrent	$ 6,509		$ 6,356	$ 6,751
Other Regulatory Liabilities | Minimum [Member]
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 1 year
Other Regulatory Liabilities | Maximum [Member]
Regulatory Assets and Liabilities
Estimated Recovery or Refund Period as of March 31, 2021	Up to 18 years
Increased Gas Costs
Regulatory Assets and Liabilities
Total regulatory assets		$ 44,000

Fair value measurements Insuran

Fair value measurements Insurance contracts (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Investments used to satisfy nonqualified benefit plans obligations	$ 101,600,000	$ 83,300,000	$ 100,100,000
Net unrealized gain (loss) on investments used to satisfy obligations under nonqualified benefit plans	$ 127,000	$ (3,700,000)

Available-for-sale securities (

Available-for-sale securities (Details 2) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Available-for-sale securities [Abstract]
Cost	$ 11,345	$ 11,185	$ 10,864
Gross Unrealized Gains	155	156	248
Gross Unrealized Losses	24	14	0
Fair Value	11,476	11,327	11,112
Mortgage-backed securities
Available-for-sale securities [Abstract]
Cost	8,709	9,799	9,691
Gross Unrealized Gains	155	156	236
Gross Unrealized Losses	10	9	0
Fair Value	8,854	9,946	9,927
U.S. Treasury securities
Available-for-sale securities [Abstract]
Cost	2,636	1,386	1,173
Gross Unrealized Gains	0	0	12
Gross Unrealized Losses	14	5	0
Fair Value	$ 2,622	$ 1,381	$ 1,185

Fair value measurements (Detail

Fair value measurements (Details 3) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Concentration risks, percentage [Abstract]
Percentage in fixed-income and other investments	54.00%	57.00%	58.00%
Percentage investment in common stock of large-cap companies	19.00%	18.00%	20.00%
Percentage investment in common stock of mid-cap companies	10.00%	9.00%	8.00%
Percentage investment in common stock of small-cap companies	9.00%	9.00%	8.00%
Percentage investment in target date investments	6.00%	5.00%	4.00%
Percentage investment in cash and cash equivalents	2.00%	2.00%	2.00%
Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 122,496	$ 120,348	$ 102,836
Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	122,496	120,348	102,836
Money market funds | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	9,388	8,917	8,470
Money market funds | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	9,388	8,917	8,470
Insurance contracts* | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	101,632	100,104	83,254
Insurance contracts* | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	101,632	100,104	83,254
Mortgage-backed securities | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	8,854	9,946	9,927
Mortgage-backed securities | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	8,854	9,946	9,927
U.S. Treasury securities | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	2,622	1,381	1,185
U.S. Treasury securities | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 2,622	$ 1,381	$ 1,185

Fair value measurements (Deta_2

Fair value measurements (Details 4) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Fair value, balance sheet grouping [Line Items]
Long-term debt	$ 2,253,274	$ 2,213,130	$ 2,455,235
Carrying amount
Fair value, balance sheet grouping [Line Items]
Long-term debt	2,253,274	2,213,130	2,455,235
Fair value
Fair value, balance sheet grouping [Line Items]
Long-term debt, fair value	$ 2,473,806	$ 2,537,289	$ 2,618,297

Long-term debt outstanding (Det

Long-term debt outstanding (Details 1) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Long-term debt outstanding [Line Items]
Long-term debt	$ 2,253,274	$ 2,213,130	$ 2,455,235
Long-term debt due within one year	1,552	1,555	16,560
Long-term debt	$ 2,251,722	2,211,575	2,438,675
Senior Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	4.40%
Long-term debt	$ 1,950,000	1,950,000	1,850,000
Commercial Paper
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	0.33%
Long-term debt	$ 218,900	125,600	265,000
Credit Agreements
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	2.20%
Long-term debt	$ 43,350	95,900	259,550
Medium-term Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	7.32%
Long-term debt	$ 35,000	35,000	50,000
Term Loan Agreements
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	2.00%
Long-term debt	$ 8,400	8,400	9,100
Other Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	0.82%
Long-term debt	$ 3,282	4,034	28,374
Long-term Debt
Long-term debt outstanding [Line Items]
Unamortized Debt Issuance Costs	5,655	5,803	6,640
Discount	$ 3	$ 1	$ 149

Schedule of debt maturities (De

Schedule of debt maturities (Details 2) $ in Thousands	Mar. 31, 2021USD ($)
Long-term debt maturities [Line Items]
Remainder of 2021	$ 780
2022	148,021
2023	77,921
2024	323,672
2025	177,802
Thereafter	$ 1,530,736

Cash flow information (Details)

Cash flow information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Supplemental Cash Flow Information [Abstract]
Interest, net*	$ 14,303,000	$ 15,978,000
Income taxes paid (refunded), net	13,880,000	(1,000)
AFUDC borrowed	348,000	627,000
Right-of-use assets obtained in exchange for new operating lease liabilities	9,236,000	10,655,000	$ 54,356,000
Property, plant and equipment additions in accounts payable	20,594,000	27,425,000	26,082,000
Accrual for holdback payment related to a business combination	$ 0	$ 5,000,000	$ 2,500,000

Business segment data (Details)

Business segment data (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 1,227,938	$ 1,197,373
Operating income (loss)	85,164	57,070
Income from continuing operations	52,116	25,539
Income (loss) from discontinued operations, net of tax	15	(409)
Net income	52,131	25,130
Electric
Segment Reporting Information [Line Items]
Revenues	84,673	85,908
Operating income (loss)	13,865	14,859
Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	350,206	326,443
Operating income (loss)	53,573	49,998
Pipeline
Segment Reporting Information [Line Items]
Revenues	9,913	10,655
Operating income (loss)	12,536	11,419
Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	265,659	262,144
Operating income (loss)	(34,889)	(43,269)
Construction services
Segment Reporting Information [Line Items]
Revenues	517,470	512,205
Operating income (loss)	40,277	23,796
Other
Segment Reporting Information [Line Items]
Revenues	17	18
Operating income (loss)	(198)	267
Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(30,935)	(31,085)
Intersegment eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	(136)	(195)
Intersegment eliminations | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	(142)	(185)
Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	(26,229)	(25,199)
Intersegment eliminations | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	(62)	(63)
Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	(1,042)	(2,470)
Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	(3,324)	(2,973)
Total intersegment operating revenues
Segment Reporting Information [Line Items]
Revenues	0	0
Regulated operation
Segment Reporting Information [Line Items]
Revenues	442,381	418,682
Income from continuing operations	56,121	51,129
Regulated operation | Electric
Segment Reporting Information [Line Items]
Revenues	84,673	85,908
Income from continuing operations	10,749	11,374
Regulated operation | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	350,206	326,443
Income from continuing operations	36,178	32,369
Regulated operation | Pipeline
Segment Reporting Information [Line Items]
Revenues	7,502	6,331
Income from continuing operations	9,194	7,386
Regulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	26,268	25,563
Regulated operation | Intersegment eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	136	195
Regulated operation | Intersegment eliminations | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	142	185
Regulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	25,990	25,183
Nonregulated operation
Segment Reporting Information [Line Items]
Revenues	785,557	778,691
Income from continuing operations	(4,005)	(25,590)
Nonregulated operation | Pipeline
Segment Reporting Information [Line Items]
Revenues	2,411	4,324
Income from continuing operations	(296)	(13)
Nonregulated operation | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	265,659	262,144
Income from continuing operations	(30,813)	(38,215)
Nonregulated operation | Construction services
Segment Reporting Information [Line Items]
Revenues	517,470	512,205
Income from continuing operations	29,825	16,823
Nonregulated operation | Other
Segment Reporting Information [Line Items]
Revenues	17	18
Income from continuing operations	(2,721)	(4,185)
Nonregulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	4,667	5,522
Nonregulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	239	16
Nonregulated operation | Intersegment eliminations | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	62	63
Nonregulated operation | Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	1,042	2,470
Nonregulated operation | Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	$ 3,324	$ 2,973

Employee benefit plans (Details

Employee benefit plans (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Qualified plan | Underfunded plan | Pension benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	$ 0	$ 0
Interest cost	2,455,000	2,973,000
Expected return on assets	(4,894,000)	(4,761,000)
Amortization of prior service credit	0	0
Amortization of net actuarial loss	2,004,000	1,863,000
Net periodic benefit cost (credit), including amount capitalized	(435,000)	75,000
Less amount capitalized	0	0
Net periodic benefit cost (credit)	(435,000)	75,000
Qualified plan | Overfunded Plan | Other postretirement benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	400,000	352,000
Interest cost	466,000	591,000
Expected return on assets	(1,275,000)	(1,248,000)
Amortization of prior service credit	(349,000)	(297,000)
Amortization of net actuarial loss	6,000	2,000
Net periodic benefit cost (credit), including amount capitalized	(752,000)	(600,000)
Less amount capitalized	39,000	32,000
Net periodic benefit cost (credit)	(791,000)	(632,000)
Nonqualified plan | Unfunded plan | Supplemental employee retirement plans
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Net periodic benefit cost (credit)	$ 769,000	$ 1,000,000

IPUC (Details)

IPUC (Details) - Pending Rate Case [Member] - IPUC - Intermountain Gas - Gas Distribution [Member] $ in Millions	Jan. 12, 2021USD ($)
Public Utilities, General Disclosures [Line Items]
Depreciation and Amortization Rate Case	$ (2.9)
Depreciation and Amortization, Rate, Percent	3.00%
Depreciation and Amortization, Requested Rate, Percent	2.60%

MNPUC (Details 2)

MNPUC (Details 2) - MNPUC [Member] - Gas Distribution [Member] - Great Plains Natural Gas Co. [Member] - USD ($) $ in Millions	Apr. 01, 2021	Mar. 30, 2021	Jan. 01, 2020	Sep. 27, 2019
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 2.9
Public Utilities, Requested Rate Increase (Decrease), Percentage				12.00%
Public Utilities, Interim Rate Increase (Decrease), Amount			$ 2.6
Public Utilities, Interim Rate Increase (Decrease), Percentage			11.00%
Pending Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 11.1
Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 2.6
Public Utilities, Approved Rate Increase (Decrease), Percentage	11.50%

NDPSC (Details 3)

NDPSC (Details 3) - Gas Distribution [Member] - NDPSC [Member] - Montana-Dakota Utilities Co. [Member] - USD ($)	Jun. 01, 2021	Mar. 31, 2021	Mar. 02, 2021	Jan. 01, 2021	Aug. 26, 2020
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 9,000,000
Public Utilities, Requested Rate Increase (Decrease), Percentage					7.80%
Public Utilities, Interim Rate Increase (Decrease), Amount				$ 6,900,000
Public Utilities, Interim Rate Increase (Decrease), Percentage				6.00%
Generation Resource Recovery Rider			$ 0
Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 6,900,000
Public Utilities, Approved Rate Increase (Decrease), Percentage	6.00%
Pending Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 13,500,000

SDPUC (Details 4)

SDPUC (Details 4) - SDPUC - Montana-Dakota Utilities Co. [Member] - USD ($)	May 01, 2021	Mar. 11, 2021
Electricity [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Total Transmission Cost Adjustment Rider	$ 1,000,000
Transmission Capital Projects Increase (Decrease)	274,000
Total Infrastructure Rider	1,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount	(236,000)
Gas Distribution [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 5,500,000
Pending Rate Case [Member] | Electricity [Member]
Public Utilities, General Disclosures [Line Items]
Total Infrastructure Rider		$ 0

WUTC (Details 5)

WUTC (Details 5) - Pending Rate Case [Member] - Gas Distribution [Member] - WUTC [Member] - Cascade Natural Gas [Member] - USD ($) $ in Millions	Jan. 08, 2021	Jul. 24, 2020	Jun. 19, 2020
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 13.8
Public Utilities, Requested Rate Increase (Decrease), Percentage			5.30%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 7.4	$ 14.3
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage	2.80%	5.50%

WYPSC (Details 6)

WYPSC (Details 6) $ in Millions	May 01, 2021USD ($)
WYPSC | Montana-Dakota Utilities Co. [Member] | Gas Distribution [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 1.6

Litigation (Details)

Litigation (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Loss Contingencies [Line Items]
Potential liabilities related to litigation and environmental matters	$ 55	$ 41.5	$ 33.1
Insurance Receivable	31.6	17.5	19
Regulatory Assets	$ 20.9	$ 21.3	$ 10.8

Guarantees (Details 2)

Guarantees (Details 2)	Mar. 31, 2021USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 235,800,000
Fixed maximum amounts guaranteed by year 2021	120,800,000
Fixed maximum amounts guaranteed by year 2022	42,400,000
Fixed maximum amounts guaranteed by year 2023	61,900,000
Fixed maximum amounts guaranteed by year 2024	500,000
Fixed maximum amounts guaranteed by year 2025	500,000
Fixed maximum amounts guaranteed, thereafter	700,000
No scheduled maturity date	9,000,000
Amount outstanding under guarantees that is reflected on balance sheet	0
Letters of credit	25,500,000
Letters of credit set to expire - 2021	23,600,000
Letters of credit set to expire - 2022	1,900,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	$ 1,100,000,000

Variable interest entities (Det

Variable interest entities (Details 3) $ in Millions	Mar. 31, 2021USD ($)
Fuel contract
Variable Interest Entities [Line Items]
Variable interest entity, reporting entity involvement, maximum loss exposure, amount	$ 33.1