MDU Resources (MDU) 10-Q 5 Aug 21 2021 Q2 Quarterly report Financial data

Cover page

Cover page - shares	6 Months Ended
	Jun. 30, 2021	Jul. 29, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 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		202,430,930
Entity Central Index Key	0000067716
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating revenues:
Operating revenues:	$ 1,423,657	$ 1,362,928	$ 2,651,595	$ 2,560,302
Operating expenses:
Operation and maintenance:	1,077,796	1,029,171	1,889,454	1,850,171
Purchased natural gas sold	63,213	56,844	239,450	222,256
Depreciation, depletion and amortization	73,661	71,508	147,384	140,747
Taxes, other than income	53,189	52,584	115,724	116,696
Electric fuel and purchased power	18,109	14,567	36,730	35,107
Total operating expenses	1,285,968	1,224,674	2,428,742	2,364,977
Operating income	137,689	138,254	222,853	195,325
Other income	9,027	10,063	12,381	9,058
Interest expense	23,381	24,818	46,835	49,371
Income before income taxes	123,335	123,499	188,399	155,012
Income taxes	23,164	23,657	36,112	29,631
Income from continuing operations	100,171	99,842	152,287	125,381
Income (loss) from discontinued operations, net of tax	19	(139)	34	(548)
Net income	$ 100,190	$ 99,703	$ 152,321	$ 124,833
Earnings per share - basic:
Income from continuing operations	$ 0.50	$ 0.50	$ 0.76	$ 0.62
Discontinued operations, net of tax	0	0	0	0
Earnings per share - basic	0.50	0.50	0.76	0.62
Earnings per share - diluted:
Income from continuing operations	0.50	0.50	0.76	0.62
Discontinued operations, net of tax	0	0	0	0
Earnings per share - diluted	$ 0.50	$ 0.50	$ 0.76	$ 0.62
Weighted average common shares outstanding - basic	201,345	200,522	201,028	200,481
Weighted average common shares outstanding - diluted	201,693	200,539	201,328	200,497
Regulated operation
Operating revenues:
Operating revenues:	$ 260,568	$ 241,353	$ 702,951	$ 660,035
Operating expenses:
Operation and maintenance:	89,404	83,103	183,737	170,712
Income from continuing operations	17,686	19,878	73,808	71,007
Nonregulated operation
Operating revenues:
Operating revenues:	1,163,089	1,121,575	1,948,644	1,900,267
Operating expenses:
Operation and maintenance:	988,392	946,068	1,705,717	1,679,459
Income from continuing operations	$ 82,485	$ 79,964	$ 78,479	$ 54,374

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net income	$ 100,190	$ 99,703	$ 152,321	$ 124,833
Other comprehensive income:
Reclassification adjustment for loss on derivative instruments included in net income, tax	36	36	73	72
Reclassification adjustment for loss on derivative instruments included in net income, net of tax	112	112	223	223
Postretirement liability adjustment:
Amortization of postretirement liability losses included in net periodic benefit cost, tax	160	155	311	304
Amortization of postretirement liability losses included in net periodic benefit cost, net of tax	457	480	923	942
Net unrealized gain (loss) on available-for-sale investments:
Net unrealized gain (loss) on available-for-sale investments arising during the period, tax	(13)	(4)	(25)	32
Net unrealized gain (loss) on available-for-sale investments arising during the period, net of tax	(52)	(13)	(96)	122
Reclassification adjustment for loss on available-for-sale investments included in net income, tax	6	2	15	2
Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax	25	7	60	6
Net unrealized gain (loss) on available-for-sale investments	(27)	(6)	(36)	128
Other comprehensive income	542	586	1,110	1,293
Comprehensive income attributable to common stockholders	$ 100,732	$ 100,289	$ 153,431	$ 126,126

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Current assets:
Cash and cash equivalents	$ 57,946	$ 59,547	$ 64,358
Receivables, net	903,831	873,986	920,824
Inventories	316,328	291,167	302,837
Current regulatory assets	109,581	68,527	60,557
Prepayments and other current assets	74,259	44,120	48,194
Total current assets	1,461,945	1,337,347	1,396,770
Noncurrent assets:
Property, plant and equipment	8,417,559	8,300,770	8,063,435
Less accumulated depreciation, depletion and amortization	3,129,717	3,133,831	3,064,833
Net property, plant and equipment	5,287,842	5,166,939	4,998,602
Goodwill	717,863	714,963	708,664
Other intangible assets, net	23,401	25,496	31,515
Regulatory assets	376,913	379,381	351,025
Investments	173,157	165,022	154,779
Operating lease right-of-use assets	112,437	120,113	115,751
Other	144,653	144,111	154,026
Total noncurrent assets	6,836,266	6,716,025	6,514,362
Total assets	8,298,211	8,053,372	7,911,132
Current liabilities:
Short-term borrowings	50,000	50,000	75,000
Long-term debt due within one year	1,549	1,555	16,560
Accounts payable	431,878	426,264	433,362
Taxes payable	78,805	88,844	80,882
Dividends payable	42,791	42,611	41,608
Accrued compensation	95,909	90,629	85,525
Regulatory liabilities due within one year	23,454	31,450	48,000
Operating lease liabilities due within one year	31,787	33,655	31,985
Other accrued liabilities	188,187	198,514	186,797
Total current liabilities	944,360	963,522	999,719
Noncurrent liabilities:
Long-term debt	2,335,500	2,211,575	2,265,316
Deferred income taxes	538,633	516,098	516,760
Asset retirement obligations	450,620	440,356	422,169
Regulatory liabilities	428,467	428,075	438,652
Operating lease liabilities	81,052	86,868	84,302
Other	320,777	327,773	286,527
Total noncurrent liabilities	4,155,049	4,010,745	4,013,726
Commitments and contingencies
Stockholders' equity:
Common stock	202,822	201,061	201,061
Other paid-in capital	1,422,169	1,371,385	1,363,182
Retained earnings	1,624,405	1,558,363	1,377,879
Accumulated other comprehensive loss	(46,968)	(48,078)	(40,809)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)	(3,626)
Total stockholders' equity	3,198,802	3,079,105	2,897,687
Total liabilities and stockholders' equity	$ 8,298,211	$ 8,053,372	$ 7,911,132
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	202,822,301	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
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, 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	124,833
Other comprehensive income	1,293
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	$ (362)
Common stock balance (in shares) at Jun. 30, 2020	201,061,198	201,061,198
Treasury stock (in shares) at Jun. 30, 2020						(538,921)
Balance at Jun. 30, 2020	$ 2,897,687	$ 201,061	1,363,182	1,377,879	(40,809)	$ (3,626)
Common stock balance (in shares) at Mar. 31, 2020		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)
Net income	99,703			99,703
Other comprehensive income	586				586
Dividends declared on common stock	(41,812)			(41,812)
Stock-based compensation	$ 2,618		2,618
Common stock balance (in shares) at Jun. 30, 2020	201,061,198	201,061,198
Treasury stock (in shares) at Jun. 30, 2020						(538,921)
Balance at Jun. 30, 2020	$ 2,897,687	$ 201,061	1,363,182	1,377,879	(40,809)	$ (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
Repurchase of common stock						(392,294)
Repurchase of common stock	(6,701)					$ (6,701)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings			(10,828)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings						392,294
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings						$ 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
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)
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	152,321
Other comprehensive income	1,110
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	$ (4,127)
Common stock balance (in shares) at Jun. 30, 2021	202,822,301	202,822,301
Treasury stock (in shares) at Jun. 30, 2021						(538,921)
Balance at Jun. 30, 2021	$ 3,198,802	$ 202,822	1,422,169	1,624,405	(46,968)	$ (3,626)
Common stock balance (in shares) at Mar. 31, 2021		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)
Net income	100,190			100,190
Other comprehensive income	542				542
Dividends declared on common stock	(43,336)			(43,336)
Stock-based compensation	6,150		6,150
Issuance of common stock (shares)		1,088,843
Issuance of common stock	$ 34,950	$ 1,089	33,861
Common stock balance (in shares) at Jun. 30, 2021	202,822,301	202,822,301
Treasury stock (in shares) at Jun. 30, 2021						(538,921)
Balance at Jun. 30, 2021	$ 3,198,802	$ 202,822	$ 1,422,169	$ 1,624,405	$ (46,968)	$ (3,626)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating activities:
Net income	$ 152,321	$ 124,833
Income (loss) from discontinued operations, net of tax	34	(548)
Income from continuing operations	152,287	125,381
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	147,384	140,747
Deferred income taxes	14,498	2,881
Changes in current assets and liabilities, net of acquisitions:
Receivables	(18,516)	(40,801)
Inventories	(25,330)	(26,276)
Other current assets	(52,768)	30,790
Accounts payable	(3,845)	13,387
Other current liabilities	(22,605)	26,612
Other noncurrent changes	(8,236)	(10,923)
Net cash provided by continuing operations	182,869	261,798
Net cash used in discontinued operations	(58)	(396)
Net cash provided by operating activities	182,811	261,402
Investing activities:
Capital expenditures	(261,937)	(248,800)
Acquisitions, net of cash acquired	(13,721)	(70,729)
Net proceeds from sale or disposition of property and other	12,402	22,968
Investments	(3,244)	23
Net cash used in investing activities	(266,500)	(296,538)
Financing activities:
Issuance of short-term borrowings	50,000	75,000
Repayment of short-term borrowings	(50,000)	0
Issuance of long-term debt	171,769	200,400
Repayment of long-term debt	(48,151)	(162,225)
Proceeds from issuance of common stock	54,649	3,410
Dividends paid	(85,351)	(83,188)
Repurchase of common stock	(6,701)	0
Tax withholding on stock-based compensation	(4,127)	(362)
Net cash provided by financing activities	82,088	33,035
Decrease in cash and cash equivalents	(1,601)	(2,101)
Cash and cash equivalents -- beginning of year	59,547	66,459
Cash and cash equivalents -- end of period	$ 57,946	$ 64,358

Basis of presentation

Basis of presentation	6 Months Ended
	Jun. 30, 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 to our country and our communities and, as a result, operations have generally continued throughout the COVID-19 pandemic and reopening of the country's economy. The Company has assessed the impacts of the COVID-19 pandemic on its results of operations for the six months ended June 30, 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	6 Months Ended
	Jun. 30, 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 removed disclosures that are no longer considered cost beneficial, clarified the specific requirements of disclosures and added disclosure requirements identified as relevant. The guidance added, 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 removed, 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 effect a one percentage point change in assumed health care cost trend rates would 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 removed exceptions on intraperiod tax allocations and reporting and provided 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 applied 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	6 Months Ended
	Jun. 30, 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	6 Months Ended
	Jun. 30, 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 $34.2 million, $45.1 million and $43.9 million at June 30, 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 Current expected credit loss provision (110) (103) — 11 (639) (841) Less write-offs charged against the allowance 341 787 — 232 64 1,424 Credit loss recoveries collected 100 199 — — — 299 At June 30, 2021 $ 327 $ 2,259 $ 2 $ 4,621 $ 3,539 $ 10,748 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 Current expected credit loss provision 303 190 — (314) 896 1,075 Less write-offs charged against the allowance 224 677 — 44 454 1,399 Credit loss recoveries collected 88 201 — — — 289 At June 30, 2020 $ 659 $ 1,531 $ — $ 5,625 $ 3,275 $ 11,090

Inventories and natural gas in

Inventories and natural gas in storage	6 Months Ended
	Jun. 30, 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: June 30, 2021 June 30, 2020 December 31, 2020 (In thousands) Aggregates held for resale $ 183,977 $ 165,357 $ 175,782 Asphalt oil 51,500 57,207 28,238 Materials and supplies 27,969 27,805 25,142 Merchandise for resale 26,871 22,974 21,087 Natural gas in storage (current) 10,824 11,776 21,919 Other 15,187 17,718 18,999 Total $ 316,328 $ 302,837 $ 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 June 30, 2021 and December 31, 2020, and $48.3 million at June 30, 2020.

Earnings per share

Earnings per share	6 Months Ended
	Jun. 30, 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 Six Months Ended June 30, June 30, 2021 2020 2021 2020 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 201,345 200,522 201,028 200,481 Effect of dilutive performance share awards and restricted stock units 348 17 300 16 Weighted average common shares outstanding - diluted 201,693 200,539 201,328 200,497 Shares excluded from the calculation of diluted earnings per share — 187 — 191 Dividends declared per common share $ .2125 $ .2075 $ .4250 $ .4150

Equity

Equity	6 Months Ended
	Jun. 30, 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 J.P. Morgan Securities LLC and MUFG Securities Americas Inc., as sales agents. This agreement, as amended, 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. As of June 30, 2021, the Company had capacity to issue up to 4.6 million additional shares of common stock under the "at-the-market" offering program. Details of the Company's "at-the-market" offering activity was as follows: Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (In millions) Shares issued 1.1 — 1.8 — Net proceeds * $ 34.9 $ — $ 54.6 $ — Issuance costs $ .4 $ — $ .7 $ — * Net proceeds were used for capital expenditures.

Accumulated other comprehensive

Accumulated other comprehensive income (loss)	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Accumulated other comprehensive income (loss)	Accumulated other 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) Other comprehensive loss before reclassifications — — (52) (52) Amounts reclassified from accumulated other comprehensive loss 112 457 25 594 Net current-period other comprehensive income (loss) 112 457 (27) 542 At June 30, 2021 $ (761) $ (46,284) $ 77 $ (46,968) 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 from (to) 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) Other comprehensive loss before reclassifications — — (13) (13) Amounts reclassified from accumulated other comprehensive loss 112 480 7 599 Net current-period other comprehensive income (loss) 112 480 (6) 586 At June 30, 2020 $ (1,207) $ (39,792) $ 190 $ (40,809) 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 Six Months Ended Location on Consolidated June 30, June 30, 2021 2020 2021 2020 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ (148) $ (148) $ (296) $ (295) Interest expense 36 36 73 72 Income taxes (112) (112) (223) (223) Amortization of postretirement liability losses included in net periodic benefit cost (617) (635) (1,234) (1,246) Other income 160 155 311 304 Income taxes (457) (480) (923) (942) Reclassification adjustment on available-for-sale investments included in net income (31) (9) (75) (8) Other income 6 2 15 2 Income taxes (25) (7) (60) (6) Total reclassifications $ (594) $ (599) $ (1,206) $ (1,171)

Revenue from contracts with cus

Revenue from contracts with customers	6 Months Ended
	Jun. 30, 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 June 30, 2021 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 29,258 $ 83,480 $ — $ — $ — $ — $ 112,738 Commercial utility sales 33,834 47,612 — — — — 81,446 Industrial utility sales 10,354 6,180 — — — — 16,534 Other utility sales 1,825 — — — — — 1,825 Natural gas transportation — 11,451 27,685 — — — 39,136 Natural gas storage — — 3,094 — — — 3,094 Contracting services — — — 280,834 — — 280,834 Construction materials — — — 498,762 — — 498,762 Intrasegment eliminations — — — (145,780) — — (145,780) Inside specialty contracting — — — — 347,702 — 347,702 Outside specialty contracting — — — — 165,123 — 165,123 Other 9,465 2,794 4,810 — 57 3,389 20,515 Intersegment eliminations (136) (142) (7,862) (142) (797) (3,361) (12,440) Revenues from contracts with customers 84,600 151,375 27,727 633,674 512,085 28 1,409,489 Revenues out of scope (950) 2,413 46 — 12,659 — 14,168 Total external operating revenues $ 83,650 $ 153,788 $ 27,773 $ 633,674 $ 524,744 $ 28 $ 1,423,657 Three Months Ended June 30, 2020 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 27,954 $ 78,653 $ — $ — $ — $ — $ 106,607 Commercial utility sales 29,877 41,027 — — — — 70,904 Industrial utility sales 8,072 5,658 — — — — 13,730 Other utility sales 1,591 — — — — — 1,591 Natural gas transportation — 10,350 27,965 — — — 38,315 Natural gas gathering — — 1,181 — — — 1,181 Natural gas storage — — 3,104 — — — 3,104 Contracting services — — — 303,356 — — 303,356 Construction materials — — — 482,498 — — 482,498 Intrasegment eliminations — — — (164,719) — — (164,719) Inside specialty contracting — — — — 324,921 — 324,921 Outside specialty contracting — — — — 160,696 — 160,696 Other 7,717 2,711 3,363 — 412 2,861 17,064 Intersegment eliminations (196) (185) (7,999) (90) (779) (2,973) (12,222) Revenues from contracts with customers 75,015 138,214 27,614 621,045 485,250 (112) 1,347,026 Revenues out of scope 1,423 3,280 44 — 11,155 — 15,902 Total external operating revenues $ 76,438 $ 141,494 $ 27,658 $ 621,045 $ 496,405 $ (112) $ 1,362,928 Six Months Ended June 30, 2021 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 62,694 $ 286,617 $ — $ — $ — $ — $ 349,311 Commercial utility sales 66,762 167,664 — — — — 234,426 Industrial utility sales 20,383 14,992 — — — — 35,375 Other utility sales 3,391 — — — — — 3,391 Natural gas transportation — 23,903 57,102 — — — 81,005 Natural gas storage — — 7,123 — — — 7,123 Contracting services — — — 376,859 — — 376,859 Construction materials — — — 715,174 — — 715,174 Intrasegment eliminations — — — (192,496) — — (192,496) Inside specialty contracting — — — — 702,892 — 702,892 Outside specialty contracting — — — — 316,486 — 316,486 Other 19,238 5,803 7,470 — 93 6,730 39,334 Intersegment eliminations (271) (284) (34,092) (204) (1,839) (6,685) (43,375) Revenues from contracts with customers 172,197 498,695 37,603 899,333 1,017,632 45 2,625,505 Revenues out of scope (3,873) 5,299 82 — 24,582 — 26,090 Total external operating revenues $ 168,324 $ 503,994 $ 37,685 $ 899,333 $ 1,042,214 $ 45 $ 2,651,595 Six Months Ended June 30, 2020 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 60,303 $ 265,354 $ — $ — $ — $ — $ 325,657 Commercial utility sales 63,464 156,023 — — — — 219,487 Industrial utility sales 18,439 14,179 — — — — 32,618 Other utility sales 3,239 — — — — — 3,239 Natural gas transportation — 22,148 55,397 — — — 77,545 Natural gas gathering — — 3,271 — — — 3,271 Natural gas storage — — 6,150 — — — 6,150 Contracting services — — — 401,757 — — 401,757 Construction materials — — — 690,408 — — 690,408 Intrasegment eliminations — — — (208,823) — — (208,823) Inside specialty contracting — — — — 697,130 — 697,130 Outside specialty contracting — — — — 290,846 — 290,846 Other 16,167 5,209 6,604 — 763 5,852 34,595 Intersegment eliminations (391) (370) (33,198) (152) (3,249) (5,946) (43,306) Revenues from contracts with customers 161,221 462,543 38,224 883,190 985,490 (94) 2,530,574 Revenues out of scope 1,125 5,394 89 — 23,120 — 29,728 Total external operating revenues $ 162,346 $ 467,937 $ 38,313 $ 883,190 $ 1,008,610 $ (94) $ 2,560,302 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: June 30, 2021 December 31, 2020 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 147,033 $ 104,345 $ 42,688 Receivables, net Contract liabilities - current (146,116) (158,603) 12,487 Accounts payable Contract liabilities - noncurrent (160) (52) (108) Noncurrent liabilities - other Net contract assets (liabilities) $ 757 $ (54,310) $ 55,067 The Company recognized $21.9 million and $145.3 million in revenue for the three and six months ended June 30, 2021, respectively, which was previously included in contract liabilities at December 31, 2020. The Company recognized $32.3 million and $121.7 million in revenue for the three and six months ended June 30, 2020, respectively, which was previously included in contract liabilities at December 31, 2019. The Company recognized a net increase in revenues of $27.3 million and $54.6 million for the three and six months ended June 30, 2021, respectively, from performance obligations satisfied in prior periods. The Company recognized a net increase in revenues of $31.9 million and $42.9 million for the three and six months ended June 30, 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 June 30, 2021, the Company's remaining performance obligations were $2.4 billion. The Company expects to recognize the following revenue amounts in future periods related to these remaining performance obligations: $1.8 billion within the next 12 months or less; $339.5 million within the next 13 to 24 months; and $225.9 million in 25 months or more.

Business Combinations

Business Combinations	6 Months Ended
	Jun. 30, 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 2021 and 2020, the construction materials and contracting segment's acquisitions included: • Mt. Hood Rock, a construction aggregates business in Oregon, was acquired in April 2021. At June 30, 2021, the purchase price allocation was preliminary and will be finalized within 12 months of the acquisition date. • The assets of McMurry Ready-Mix Co., an aggregates and concrete supplier in Wyoming, were acquired in December 2020. At June 30, 2021, the purchase price allocation was preliminary and will be finalized within 12 months of the acquisition date. In the second quarter of 2021, the Company made a purchase price adjustment, which was not material, to the provisional accounting and is reflected in the 2021 allocated amounts below. • The assets of Oldcastle Infrastructure Spokane, a prestressed-concrete business in Washington, were acquired in February 2020. As of December 31, 2020, the purchase price adjustments had been settled with no material adjustments to the provisional accounting. In February 2020, the construction services segment acquired PerLectric, Inc., an electrical construction company in Virginia. As of March 31, 2021, the purchase price adjustments had been settled with no material adjustments to the provisional accounting. In 2021, the total purchase price for acquisitions was $13.8 million, subject to certain adjustments, with cash acquired totaling $100,000. The purchase price includes consideration paid of $13.7 million. The amounts allocated to the aggregated assets acquired and liabilities assumed during 2021 were as follows: $700,000 to current assets; $13.0 million to property, plant and equipment; $2.9 million to goodwill; $600,000 to other intangible assets; $200,000 to current liabilities; $100,000 to noncurrent liabilities and $3.2 million to deferred tax liabilities. The Company issued debt to finance the acquisitions. In 2020, the total purchase price for acquisitions 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. The Company issued debt to finance the acquisitions. Costs incurred for acquisitions are included in operation and maintenance expense on the Consolidated Statements of Income and were not material for the six months ended June 30, 2021 and 2020.

Leases

Leases	6 Months Ended
	Jun. 30, 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 $12.8 million and $24.8 million for the three and six months ended June 30, 2021, respectively. The Company recognized revenue from operating leases of $11.2 million and $23.3 million for the three and six months ended June 30, 2020, respectively. At June 30, 2021, the Company had $9.8 million of lease receivables with a majority due within 12 months.

Goodwill and other intangible a

Goodwill and other intangible assets	6 Months Ended
	Jun. 30, 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 June 30, 2021 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 226,003 2,900 — 228,903 Construction services 143,224 — — 143,224 Total $ 714,963 $ 2,900 $ — $ 717,863 Balance at January 1, 2020 Goodwill Measurement Balance at June 30, 2020 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 217,234 6,483 — 223,717 Construction services 118,388 24,436 (3,613) 139,211 Total $ 681,358 $ 30,919 $ (3,613) $ 708,664 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: June 30, 2021 June 30, 2020 December 31, 2020 (In thousands) Customer relationships $ 29,423 $ 30,087 $ 28,836 Less accumulated amortization 8,765 5,239 6,887 20,658 24,848 21,949 Noncompete agreements 3,991 4,229 3,941 Less accumulated amortization 2,576 2,084 2,309 1,415 2,145 1,632 Other 11,957 13,060 12,927 Less accumulated amortization 10,629 8,538 11,012 1,328 4,522 1,915 Total $ 23,401 $ 31,515 $ 25,496 The previous tables include goodwill and intangible assets associated with the business combinations completed during 2021 and 2020. For more information related to these business combinations, see Note 10. Amortization expense for amortizable intangible assets for the three and six months ended June 30, 2021, was $1.2 million and $2.7 million, respectively. Amortization expense for amortizable intangible assets for the three and six months ended June 30, 2020, was $2.7 million and $4.7 million, respectively. Estimated amortization expense for identifiable intangible assets as of June 30, 2021, was: Remainder of 2021 2022 2023 2024 2025 Thereafter (In thousands) Amortization expense $ 2,381 $ 4,678 $ 4,329 $ 3,957 $ 2,060 $ 5,996

Regulatory assets and liabiliti

Regulatory assets and liabilities	6 Months Ended
	Jun. 30, 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 June 30, 2021 * June 30, 2021 June 30, 2020 December 31, 2020 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 85,045 $ 42,582 $ 42,481 Conservation programs Up to 1 year 7,580 7,256 7,117 Cost recovery mechanisms Up to 1 year 5,692 7,781 10,645 Other Up to 1 year 11,264 2,938 8,284 109,581 60,557 68,527 Noncurrent: Pension and postretirement benefits ** 155,906 157,033 155,942 Plant costs/asset retirement obligations Over plant lives 72,853 68,191 71,740 Plant retirement - 46,061 49,185 65,919 Cost recovery mechanisms Up to 10 years 44,415 13,140 16,245 Manufactured gas plant site remediation - 26,155 14,826 26,429 Taxes recoverable from customers Over plant lives 10,929 10,890 10,785 Natural gas costs recoverable through rate adjustments Up to 3 years 8,389 27,184 21,539 Long-term debt refinancing costs Up to 39 years 4,110 3,980 4,426 Other Up to 18 years 8,095 6,596 6,356 376,913 351,025 379,381 Total regulatory assets $ 486,494 $ 411,582 $ 447,908 Regulatory liabilities: Current: Natural gas costs refundable through rate adjustments Up to 1 year $ 8,935 $ 29,557 $ 18,565 Electric fuel and purchased power deferral Up to 1 year 5,431 7,799 3,667 Taxes refundable to customers Up to 1 year 3,434 4,012 3,557 Other Up to 1 year 5,654 6,632 5,661 23,454 48,000 31,450 Noncurrent: Taxes refundable to customers Over plant lives 222,098 236,142 227,850 Plant removal and decommissioning costs Over plant lives 171,381 173,399 167,171 Pension and postretirement benefits ** 16,940 18,015 16,989 Other Up to 21 years 18,048 11,096 16,065 428,467 438,652 428,075 Total regulatory liabilities $ 451,921 $ 486,652 $ 459,525 Net regulatory position $ 34,573 $ (75,070) $ (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 June 30, 2021 and 2020, and December 31, 2020, approximately $317.0 million, $296.6 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 retirement 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. These extraordinary gas costs were recorded as regulatory assets as they are expected to be recovered from customers. The Company has filed out-of-cycle purchased gas adjustment requests in four out of five jurisdictions affected by this cold-weather event and has received approval in three jurisdictions. The Company will continue to engage with its regulators to determine the appropriate recovery periods over which to recover the associated natural gas costs. For a discussion of the Company's most recent cases by jurisdiction, see Note 19. 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 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 in the second quarter of 2021, the Company began amortizing plant retirement and closure costs related to this facility. 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. In the second quarter of 2021, the Company moved the costs being recovered for this facility from plant retirement to cost recovery mechanisms in the previous table. 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. For a discussion of the Company's most recent cases by jurisdiction, see Note 19. 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	6 Months Ended
	Jun. 30, 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 $105.7 million, $92.4 million and $100.1 million, at June 30, 2021 and 2020, and December 31, 2020, respectively, are classified as investments on the Consolidated Balance Sheets. The net unrealized gains on these investments were $3.8 million and $3.9 million for the three and six months ended June 30, 2021, respectively. The net unrealized gains on these investments were $9.1 million and $5.4 million for the three and six months ended June 30, 2020, respectively. 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: June 30, 2021 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 8,278 $ 127 $ 9 $ 8,396 U.S. Treasury securities 2,893 — 21 2,872 Total $ 11,171 $ 127 $ 30 $ 11,268 June 30, 2020 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,812 $ 239 $ 6 $ 10,045 U.S. Treasury securities 1,170 7 — 1,177 Total $ 10,982 $ 246 $ 6 $ 11,222 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 June 30, 2021, Using Quoted Prices in Significant Significant Balance at June 30, 2021 (In thousands) Assets: Money market funds $ — $ 12,234 $ — $ 12,234 Insurance contracts* — 105,684 105,684 Available-for-sale securities: Mortgage-backed securities — 8,396 — 8,396 U.S. Treasury securities — 2,872 — 2,872 Total assets measured at fair value $ — $ 129,186 $ — $ 129,186 * The insurance contracts invest approximately 53 percent in fixed-income investments, 20 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 June 30, 2020, Using Quoted Prices in Significant Significant Balance at June 30, 2020 (In thousands) Assets: Money market funds $ — $ 8,478 $ — $ 8,478 Insurance contract* — 92,413 — 92,413 Available-for-sale securities: Mortgage-backed securities — 10,045 — 10,045 U.S. Treasury securities — 1,177 — 1,177 Total assets measured at fair value $ — $ 112,113 $ — $ 112,113 * The insurance contract invests approximately 38 percent in fixed-income investments, 23 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, 4 percent in target date investments and 17 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 2021 and 2020. The fair value of these assets and liabilities were determined based on Level 2 and Level 3 inputs. 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: June 30, 2021 June 30, 2020 December 31, 2020 (In thousands) Carrying amount $ 2,337,049 $ 2,281,876 $ 2,213,130 Fair value $ 2,616,232 $ 2,563,734 $ 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	6 Months Ended
	Jun. 30, 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 June 30, 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 June 30, 2021 June 30, 2021 June 30, 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 $ 1,900,000 $ 1,950,000 Commercial paper supported by revolving credit agreements .32 % 297,400 290,100 125,600 Credit agreements due on June 7, 2024 3.25 % 48,550 11,200 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 January 1, 2061 .83 % 3,232 28,342 4,034 Less unamortized debt issuance costs 5,505 6,668 5,803 Less discount 28 198 1 Total long-term debt 2,337,049 2,281,876 2,213,130 Less current maturities 1,549 16,560 1,555 Net long-term debt $ 2,335,500 $ 2,265,316 $ 2,211,575 Schedule of Debt Maturities Long-term debt maturities, which excludes unamortized debt issuance costs and discount, at June 30, 2021, were as follows: Remainder of 2021 2022 2023 2024 2025 Thereafter (In thousands) Long-term debt maturities $ 752 $ 148,021 $ 77,921 $ 407,372 $ 177,802 $ 1,530,714

Cash flow information

Cash flow information	6 Months Ended
	Jun. 30, 2021
Supplemental Cash Flow Information [Abstract]
Cash flow information	Cash flow information Cash expenditures for interest and income taxes were as follows: Six Months Ended June 30, 2021 2020 (In thousands) Interest, net* $ 45,870 $ 47,769 Income taxes paid, net $ 46,734 $ 735 * AFUDC - borrowed was $816,000 and $1.3 million for the six months ended June 30, 2021 and 2020, respectively. Noncash investing and financing transactions were as follows: June 30, 2021 June 30, 2020 December 31, 2020 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 17,224 $ 24,181 $ 54,356 Property, plant and equipment additions in accounts payable $ 31,886 $ 36,493 $ 26,082 Accrual for holdback payment related to a business combination $ — $ 5,000 $ 2,500

Business segment data

Business segment data	6 Months Ended
	Jun. 30, 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 43 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 Six Months Ended June 30, June 30, 2021 2020 2021 2020 (In thousands) External operating revenues: Regulated operations: Electric $ 83,650 $ 76,438 $ 168,324 $ 162,346 Natural gas distribution 153,788 141,494 503,994 467,937 Pipeline 23,130 23,421 30,633 29,752 260,568 241,353 702,951 660,035 Non-regulated operations: Pipeline 4,643 4,237 7,052 8,561 Construction materials and contracting 633,674 621,045 899,333 883,190 Construction services 524,744 496,405 1,042,214 1,008,610 Other 28 (112) 45 (94) 1,163,089 1,121,575 1,948,644 1,900,267 Total external operating revenues $ 1,423,657 $ 1,362,928 $ 2,651,595 $ 2,560,302 Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (In thousands) Intersegment operating revenues: Regulated operations: Electric $ 136 $ 196 $ 271 $ 391 Natural gas distribution 142 185 284 370 Pipeline 7,695 7,857 33,685 33,040 7,973 8,238 34,240 33,801 Non-regulated operations: Pipeline 167 142 407 158 Construction materials and contracting 142 90 204 152 Construction services 797 779 1,839 3,249 Other 3,361 2,973 6,685 5,946 4,467 3,984 9,135 9,505 Intersegment eliminations (12,440) (12,222) (43,375) (43,306) Total intersegment operating revenues $ — $ — $ — $ — Operating income (loss): Electric $ 12,806 $ 12,810 $ 26,672 $ 27,669 Natural gas distribution 3,601 678 57,173 50,677 Pipeline 11,076 12,225 23,612 23,644 Construction materials and contracting 72,452 74,741 37,563 31,472 Construction services 37,774 37,882 78,051 61,678 Other (20) (82) (218) 185 Total operating income $ 137,689 $ 138,254 $ 222,853 $ 195,325 Net income (loss): Regulated operations: Electric $ 10,304 $ 12,153 $ 21,054 $ 23,527 Natural gas distribution (707) (959) 35,471 31,410 Pipeline 8,089 8,684 17,283 16,070 17,686 19,878 73,808 71,007 Non-regulated operations: Pipeline 1,106 268 810 255 Construction materials and contracting 51,396 53,020 20,584 14,806 Construction services 28,885 27,932 58,709 44,755 Other 1,098 (1,256) (1,624) (5,442) 82,485 79,964 78,479 54,374 Income from continuing operations 100,171 99,842 152,287 125,381 Income (loss) from discontinued operations, net of tax 19 (139) 34 (548) Net income $ 100,190 $ 99,703 $ 152,321 $ 124,833

Employee benefit plans

Employee benefit plans	6 Months Ended
	Jun. 30, 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 credit for the Company's pension and other postretirement benefit plans were as follows: Pension Benefits Other Three Months Ended June 30, 2021 2020 2021 2020 (In thousands) Components of net periodic benefit credit: Service cost $ — $ — $ 400 $ 414 Interest cost 2,455 3,074 466 627 Expected return on assets (4,894) (5,214) (1,275) (1,401) Amortization of prior service credit — — (349) (402) Amortization of net actuarial loss 2,004 1,723 6 142 Net periodic benefit credit, including amount capitalized (435) (417) (752) (620) Less amount capitalized — — 44 35 Net periodic benefit credit $ (435) $ (417) $ (796) $ (655) Pension Benefits Other Six Months Ended June 30, 2021 2020 2021 2020 (In thousands) Components of net periodic benefit credit: Service cost $ — $ — $ 800 $ 766 Interest cost 4,910 6,047 932 1,218 Expected return on assets (9,788) (9,975) (2,550) (2,649) Amortization of prior service credit — — (698) (699) Amortization of net actuarial loss 4,008 3,586 12 144 Net periodic benefit credit, including amount capitalized (870) (342) (1,504) (1,220) Less amount capitalized — — 83 67 Net periodic benefit credit $ (870) $ (342) $ (1,587) $ (1,287) The components of net periodic benefit 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 $1.5 million for the three and six months ended June 30, 2021, respectively. The Company's net periodic benefit cost for these plans for the three and six months ended June 30, 2020 was $900,000 and $1.9 million, 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	6 Months Ended
	Jun. 30, 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. On June 3, 2021, Intermountain filed a joint settlement agreement with the IPUC Staff reflecting a revised annual decrease of approximately $3.8 million or approximately 2.4 percent. Intermountain and the IPUC Staff have requested the rates be retroactive to January 1, 2021. This matter is pending before the IPUC. MNPUC 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, Great Plains 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. On June 8, 2021, the Company's request was denied; however, the MNPUC initiated its own investigation into the impact of severe weather in February 2021 on Minnesota's natural gas utility companies and consumers. The investigation will address the recovery of the extraordinary gas costs resulting from the February 2021 extreme cold weather event. MNPUC deliberations on this matter are scheduled for August 5, 2021. This matter is pending before the MNPUC. NDPSC 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, Montana-Dakota 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. On May 27, 2021, the NDPSC approved the requested increase with a recovery period of 16 months effective June 1, 2021. On July 15, 2021, Montana-Dakota filed an annual update to its transmission cost adjustment rider with the NDPSC requesting to recover revenues of approximately $14.5 million, which includes a true-up of the prior period adjustment, resulting in a decrease of approximately $1.1 million from current rates. This filing includes approximately $5.1 million related to transmission capital projects. This matter is pending before the NDPSC. SDPUC 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. 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. On May 18, 2021, the WUTC issued a final order reflecting an overall revenue decrease of approximately $391,000 or approximately 0.2 percent. On May 25, 2021, Cascade filed a petition for reconsideration with the WUTC. On June 18, 2021, the WUTC denied Cascade's petition for reconsideration. Final rates were effective July 1, 2021. On June 1, 2021, Cascade filed its annual pipeline cost recovery mechanism requesting an increase in annual revenue of approximately $2.1 million or approximately 0.8 percent. The filing includes a proposed effective date of November 1, 2021. This filing will be updated to more accurate data prior to the effective date. This matter is pending before the WUTC.

Contingencies

Contingencies	6 Months Ended
	Jun. 30, 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 June 30, 2021 and 2020, and December 31, 2020, the Company accrued liabilities which have not been discounted, including liabilities held for sale, of $30.8 million, $34.5 million and $41.5 million, respectively. At June 30, 2021 and 2020, and December 31, 2020, the Company also recorded corresponding insurance receivables of $6.9 million, $21.1 million and $17.5 million, respectively, and regulatory assets of $21.2 million, $10.4 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 June 30, 2021, the fixed maximum amounts guaranteed under these agreements aggregated $171.2 million. Certain of the guarantees also have no fixed maximum amounts specified. At June 30, 2021, the amounts of scheduled expiration of the maximum amounts guaranteed under these agreements aggregate to $37.2 million in 2021; $67.7 million in 2022; $55.6 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 June 30, 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 June 30, 2021, the fixed maximum amounts guaranteed under these letters of credit aggregated $25.5 million. At June 30, 2021, the amounts of scheduled expiration of the maximum amounts guaranteed under these letters of credit aggregate to $23.4 million in 2021 and $2.1 million in 2022. There were no amounts outstanding under the previously mentioned letters of credit at June 30, 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 June 30, 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 June 30, 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 June 30, 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 $32.6 million.

Basis of presentation (Policies

Basis of presentation (Policies)	6 Months Ended
	Jun. 30, 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)	6 Months Ended
	Jun. 30, 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 removed disclosures that are no longer considered cost beneficial, clarified the specific requirements of disclosures and added disclosure requirements identified as relevant. The guidance added, 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 removed, 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 effect a one percentage point change in assumed health care cost trend rates would 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 removed exceptions on intraperiod tax allocations and reporting and provided 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 applied 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)	6 Months Ended
	Jun. 30, 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)	6 Months Ended
	Jun. 30, 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)	6 Months Ended
	Jun. 30, 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)	6 Months Ended
	Jun. 30, 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)	6 Months Ended
	Jun. 30, 2021
Business Combinations [Abstract]
Business Combinations Policy	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)	6 Months Ended
	Jun. 30, 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)	6 Months Ended
	Jun. 30, 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)	6 Months Ended
	Jun. 30, 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)	6 Months Ended
	Jun. 30, 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 Current expected credit loss provision (110) (103) — 11 (639) (841) Less write-offs charged against the allowance 341 787 — 232 64 1,424 Credit loss recoveries collected 100 199 — — — 299 At June 30, 2021 $ 327 $ 2,259 $ 2 $ 4,621 $ 3,539 $ 10,748 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 Current expected credit loss provision 303 190 — (314) 896 1,075 Less write-offs charged against the allowance 224 677 — 44 454 1,399 Credit loss recoveries collected 88 201 — — — 289 At June 30, 2020 $ 659 $ 1,531 $ — $ 5,625 $ 3,275 $ 11,090

Inventories and natural gas i_3

Inventories and natural gas in storage (Tables)	6 Months Ended
	Jun. 30, 2021
Inventory Disclosure [Abstract]
Inventories	Inventories on the Consolidated Balance Sheets were as follows: June 30, 2021 June 30, 2020 December 31, 2020 (In thousands) Aggregates held for resale $ 183,977 $ 165,357 $ 175,782 Asphalt oil 51,500 57,207 28,238 Materials and supplies 27,969 27,805 25,142 Merchandise for resale 26,871 22,974 21,087 Natural gas in storage (current) 10,824 11,776 21,919 Other 15,187 17,718 18,999 Total $ 316,328 $ 302,837 $ 291,167

Earnings per share (Tables)

Earnings per share (Tables)	6 Months Ended
	Jun. 30, 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 Six Months Ended June 30, June 30, 2021 2020 2021 2020 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 201,345 200,522 201,028 200,481 Effect of dilutive performance share awards and restricted stock units 348 17 300 16 Weighted average common shares outstanding - diluted 201,693 200,539 201,328 200,497 Shares excluded from the calculation of diluted earnings per share — 187 — 191 Dividends declared per common share $ .2125 $ .2075 $ .4250 $ .4150

Equity (Tables)

Equity (Tables)	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Schedule of Stock by Class	Details of the Company's "at-the-market" offering activity was as follows: Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (In millions) Shares issued 1.1 — 1.8 — Net proceeds * $ 34.9 $ — $ 54.6 $ — Issuance costs $ .4 $ — $ .7 $ — * Net proceeds were used for capital expenditures.

Accumulated other comprehensi_2

Accumulated other comprehensive income (loss) (Tables)	6 Months Ended
	Jun. 30, 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) Other comprehensive loss before reclassifications — — (52) (52) Amounts reclassified from accumulated other comprehensive loss 112 457 25 594 Net current-period other comprehensive income (loss) 112 457 (27) 542 At June 30, 2021 $ (761) $ (46,284) $ 77 $ (46,968) 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 from (to) 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) Other comprehensive loss before reclassifications — — (13) (13) Amounts reclassified from accumulated other comprehensive loss 112 480 7 599 Net current-period other comprehensive income (loss) 112 480 (6) 586 At June 30, 2020 $ (1,207) $ (39,792) $ 190 $ (40,809)
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 Six Months Ended Location on Consolidated June 30, June 30, 2021 2020 2021 2020 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ (148) $ (148) $ (296) $ (295) Interest expense 36 36 73 72 Income taxes (112) (112) (223) (223) Amortization of postretirement liability losses included in net periodic benefit cost (617) (635) (1,234) (1,246) Other income 160 155 311 304 Income taxes (457) (480) (923) (942) Reclassification adjustment on available-for-sale investments included in net income (31) (9) (75) (8) Other income 6 2 15 2 Income taxes (25) (7) (60) (6) Total reclassifications $ (594) $ (599) $ (1,206) $ (1,171)

Revenue from contracts with c_3

Revenue from contracts with customers (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2021 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 29,258 $ 83,480 $ — $ — $ — $ — $ 112,738 Commercial utility sales 33,834 47,612 — — — — 81,446 Industrial utility sales 10,354 6,180 — — — — 16,534 Other utility sales 1,825 — — — — — 1,825 Natural gas transportation — 11,451 27,685 — — — 39,136 Natural gas storage — — 3,094 — — — 3,094 Contracting services — — — 280,834 — — 280,834 Construction materials — — — 498,762 — — 498,762 Intrasegment eliminations — — — (145,780) — — (145,780) Inside specialty contracting — — — — 347,702 — 347,702 Outside specialty contracting — — — — 165,123 — 165,123 Other 9,465 2,794 4,810 — 57 3,389 20,515 Intersegment eliminations (136) (142) (7,862) (142) (797) (3,361) (12,440) Revenues from contracts with customers 84,600 151,375 27,727 633,674 512,085 28 1,409,489 Revenues out of scope (950) 2,413 46 — 12,659 — 14,168 Total external operating revenues $ 83,650 $ 153,788 $ 27,773 $ 633,674 $ 524,744 $ 28 $ 1,423,657 Three Months Ended June 30, 2020 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 27,954 $ 78,653 $ — $ — $ — $ — $ 106,607 Commercial utility sales 29,877 41,027 — — — — 70,904 Industrial utility sales 8,072 5,658 — — — — 13,730 Other utility sales 1,591 — — — — — 1,591 Natural gas transportation — 10,350 27,965 — — — 38,315 Natural gas gathering — — 1,181 — — — 1,181 Natural gas storage — — 3,104 — — — 3,104 Contracting services — — — 303,356 — — 303,356 Construction materials — — — 482,498 — — 482,498 Intrasegment eliminations — — — (164,719) — — (164,719) Inside specialty contracting — — — — 324,921 — 324,921 Outside specialty contracting — — — — 160,696 — 160,696 Other 7,717 2,711 3,363 — 412 2,861 17,064 Intersegment eliminations (196) (185) (7,999) (90) (779) (2,973) (12,222) Revenues from contracts with customers 75,015 138,214 27,614 621,045 485,250 (112) 1,347,026 Revenues out of scope 1,423 3,280 44 — 11,155 — 15,902 Total external operating revenues $ 76,438 $ 141,494 $ 27,658 $ 621,045 $ 496,405 $ (112) $ 1,362,928 Six Months Ended June 30, 2021 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 62,694 $ 286,617 $ — $ — $ — $ — $ 349,311 Commercial utility sales 66,762 167,664 — — — — 234,426 Industrial utility sales 20,383 14,992 — — — — 35,375 Other utility sales 3,391 — — — — — 3,391 Natural gas transportation — 23,903 57,102 — — — 81,005 Natural gas storage — — 7,123 — — — 7,123 Contracting services — — — 376,859 — — 376,859 Construction materials — — — 715,174 — — 715,174 Intrasegment eliminations — — — (192,496) — — (192,496) Inside specialty contracting — — — — 702,892 — 702,892 Outside specialty contracting — — — — 316,486 — 316,486 Other 19,238 5,803 7,470 — 93 6,730 39,334 Intersegment eliminations (271) (284) (34,092) (204) (1,839) (6,685) (43,375) Revenues from contracts with customers 172,197 498,695 37,603 899,333 1,017,632 45 2,625,505 Revenues out of scope (3,873) 5,299 82 — 24,582 — 26,090 Total external operating revenues $ 168,324 $ 503,994 $ 37,685 $ 899,333 $ 1,042,214 $ 45 $ 2,651,595 Six Months Ended June 30, 2020 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 60,303 $ 265,354 $ — $ — $ — $ — $ 325,657 Commercial utility sales 63,464 156,023 — — — — 219,487 Industrial utility sales 18,439 14,179 — — — — 32,618 Other utility sales 3,239 — — — — — 3,239 Natural gas transportation — 22,148 55,397 — — — 77,545 Natural gas gathering — — 3,271 — — — 3,271 Natural gas storage — — 6,150 — — — 6,150 Contracting services — — — 401,757 — — 401,757 Construction materials — — — 690,408 — — 690,408 Intrasegment eliminations — — — (208,823) — — (208,823) Inside specialty contracting — — — — 697,130 — 697,130 Outside specialty contracting — — — — 290,846 — 290,846 Other 16,167 5,209 6,604 — 763 5,852 34,595 Intersegment eliminations (391) (370) (33,198) (152) (3,249) (5,946) (43,306) Revenues from contracts with customers 161,221 462,543 38,224 883,190 985,490 (94) 2,530,574 Revenues out of scope 1,125 5,394 89 — 23,120 — 29,728 Total external operating revenues $ 162,346 $ 467,937 $ 38,313 $ 883,190 $ 1,008,610 $ (94) $ 2,560,302
Contract balances	The changes in contract assets and liabilities were as follows: June 30, 2021 December 31, 2020 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 147,033 $ 104,345 $ 42,688 Receivables, net Contract liabilities - current (146,116) (158,603) 12,487 Accounts payable Contract liabilities - noncurrent (160) (52) (108) Noncurrent liabilities - other Net contract assets (liabilities) $ 757 $ (54,310) $ 55,067

Goodwill and other intangible_2

Goodwill and other intangible assets (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2021 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 226,003 2,900 — 228,903 Construction services 143,224 — — 143,224 Total $ 714,963 $ 2,900 $ — $ 717,863 Balance at January 1, 2020 Goodwill Measurement Balance at June 30, 2020 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 217,234 6,483 — 223,717 Construction services 118,388 24,436 (3,613) 139,211 Total $ 681,358 $ 30,919 $ (3,613) $ 708,664 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: June 30, 2021 June 30, 2020 December 31, 2020 (In thousands) Customer relationships $ 29,423 $ 30,087 $ 28,836 Less accumulated amortization 8,765 5,239 6,887 20,658 24,848 21,949 Noncompete agreements 3,991 4,229 3,941 Less accumulated amortization 2,576 2,084 2,309 1,415 2,145 1,632 Other 11,957 13,060 12,927 Less accumulated amortization 10,629 8,538 11,012 1,328 4,522 1,915 Total $ 23,401 $ 31,515 $ 25,496
Estimated amortization expense	Estimated amortization expense for identifiable intangible assets as of June 30, 2021, was: Remainder of 2021 2022 2023 2024 2025 Thereafter (In thousands) Amortization expense $ 2,381 $ 4,678 $ 4,329 $ 3,957 $ 2,060 $ 5,996

Regulatory assets and liabili_2

Regulatory assets and liabilities (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2021 * June 30, 2021 June 30, 2020 December 31, 2020 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 85,045 $ 42,582 $ 42,481 Conservation programs Up to 1 year 7,580 7,256 7,117 Cost recovery mechanisms Up to 1 year 5,692 7,781 10,645 Other Up to 1 year 11,264 2,938 8,284 109,581 60,557 68,527 Noncurrent: Pension and postretirement benefits ** 155,906 157,033 155,942 Plant costs/asset retirement obligations Over plant lives 72,853 68,191 71,740 Plant retirement - 46,061 49,185 65,919 Cost recovery mechanisms Up to 10 years 44,415 13,140 16,245 Manufactured gas plant site remediation - 26,155 14,826 26,429 Taxes recoverable from customers Over plant lives 10,929 10,890 10,785 Natural gas costs recoverable through rate adjustments Up to 3 years 8,389 27,184 21,539 Long-term debt refinancing costs Up to 39 years 4,110 3,980 4,426 Other Up to 18 years 8,095 6,596 6,356 376,913 351,025 379,381 Total regulatory assets $ 486,494 $ 411,582 $ 447,908 Regulatory liabilities: Current: Natural gas costs refundable through rate adjustments Up to 1 year $ 8,935 $ 29,557 $ 18,565 Electric fuel and purchased power deferral Up to 1 year 5,431 7,799 3,667 Taxes refundable to customers Up to 1 year 3,434 4,012 3,557 Other Up to 1 year 5,654 6,632 5,661 23,454 48,000 31,450 Noncurrent: Taxes refundable to customers Over plant lives 222,098 236,142 227,850 Plant removal and decommissioning costs Over plant lives 171,381 173,399 167,171 Pension and postretirement benefits ** 16,940 18,015 16,989 Other Up to 21 years 18,048 11,096 16,065 428,467 438,652 428,075 Total regulatory liabilities $ 451,921 $ 486,652 $ 459,525 Net regulatory position $ 34,573 $ (75,070) $ (11,617)
Regulatory Liabilities	The following table summarizes the individual components of unamortized regulatory assets and liabilities: Estimated Recovery or Refund Period as of June 30, 2021 * June 30, 2021 June 30, 2020 December 31, 2020 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 85,045 $ 42,582 $ 42,481 Conservation programs Up to 1 year 7,580 7,256 7,117 Cost recovery mechanisms Up to 1 year 5,692 7,781 10,645 Other Up to 1 year 11,264 2,938 8,284 109,581 60,557 68,527 Noncurrent: Pension and postretirement benefits ** 155,906 157,033 155,942 Plant costs/asset retirement obligations Over plant lives 72,853 68,191 71,740 Plant retirement - 46,061 49,185 65,919 Cost recovery mechanisms Up to 10 years 44,415 13,140 16,245 Manufactured gas plant site remediation - 26,155 14,826 26,429 Taxes recoverable from customers Over plant lives 10,929 10,890 10,785 Natural gas costs recoverable through rate adjustments Up to 3 years 8,389 27,184 21,539 Long-term debt refinancing costs Up to 39 years 4,110 3,980 4,426 Other Up to 18 years 8,095 6,596 6,356 376,913 351,025 379,381 Total regulatory assets $ 486,494 $ 411,582 $ 447,908 Regulatory liabilities: Current: Natural gas costs refundable through rate adjustments Up to 1 year $ 8,935 $ 29,557 $ 18,565 Electric fuel and purchased power deferral Up to 1 year 5,431 7,799 3,667 Taxes refundable to customers Up to 1 year 3,434 4,012 3,557 Other Up to 1 year 5,654 6,632 5,661 23,454 48,000 31,450 Noncurrent: Taxes refundable to customers Over plant lives 222,098 236,142 227,850 Plant removal and decommissioning costs Over plant lives 171,381 173,399 167,171 Pension and postretirement benefits ** 16,940 18,015 16,989 Other Up to 21 years 18,048 11,096 16,065 428,467 438,652 428,075 Total regulatory liabilities $ 451,921 $ 486,652 $ 459,525 Net regulatory position $ 34,573 $ (75,070) $ (11,617)

Fair value measurements (Tables

Fair value measurements (Tables)	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
Available-for-sale securities	Details of available-for-sale securities were as follows: June 30, 2021 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 8,278 $ 127 $ 9 $ 8,396 U.S. Treasury securities 2,893 — 21 2,872 Total $ 11,171 $ 127 $ 30 $ 11,268 June 30, 2020 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,812 $ 239 $ 6 $ 10,045 U.S. Treasury securities 1,170 7 — 1,177 Total $ 10,982 $ 246 $ 6 $ 11,222 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 June 30, 2021, Using Quoted Prices in Significant Significant Balance at June 30, 2021 (In thousands) Assets: Money market funds $ — $ 12,234 $ — $ 12,234 Insurance contracts* — 105,684 105,684 Available-for-sale securities: Mortgage-backed securities — 8,396 — 8,396 U.S. Treasury securities — 2,872 — 2,872 Total assets measured at fair value $ — $ 129,186 $ — $ 129,186 * The insurance contracts invest approximately 53 percent in fixed-income investments, 20 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 June 30, 2020, Using Quoted Prices in Significant Significant Balance at June 30, 2020 (In thousands) Assets: Money market funds $ — $ 8,478 $ — $ 8,478 Insurance contract* — 92,413 — 92,413 Available-for-sale securities: Mortgage-backed securities — 10,045 — 10,045 U.S. Treasury securities — 1,177 — 1,177 Total assets measured at fair value $ — $ 112,113 $ — $ 112,113 * The insurance contract invests approximately 38 percent in fixed-income investments, 23 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, 4 percent in target date investments and 17 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: June 30, 2021 June 30, 2020 December 31, 2020 (In thousands) Carrying amount $ 2,337,049 $ 2,281,876 $ 2,213,130 Fair value $ 2,616,232 $ 2,563,734 $ 2,537,289

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2021
Debt Disclosure [Abstract]
Long-term debt outstanding	Long-term debt outstanding was as follows: Weighted Average Interest Rate at June 30, 2021 June 30, 2021 June 30, 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 $ 1,900,000 $ 1,950,000 Commercial paper supported by revolving credit agreements .32 % 297,400 290,100 125,600 Credit agreements due on June 7, 2024 3.25 % 48,550 11,200 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 January 1, 2061 .83 % 3,232 28,342 4,034 Less unamortized debt issuance costs 5,505 6,668 5,803 Less discount 28 198 1 Total long-term debt 2,337,049 2,281,876 2,213,130 Less current maturities 1,549 16,560 1,555 Net long-term debt $ 2,335,500 $ 2,265,316 $ 2,211,575
Schedule of debt maturities	Long-term debt maturities, which excludes unamortized debt issuance costs and discount, at June 30, 2021, were as follows: Remainder of 2021 2022 2023 2024 2025 Thereafter (In thousands) Long-term debt maturities $ 752 $ 148,021 $ 77,921 $ 407,372 $ 177,802 $ 1,530,714

Cash flow information (Tables)

Cash flow information (Tables)	6 Months Ended
	Jun. 30, 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: Six Months Ended June 30, 2021 2020 (In thousands) Interest, net* $ 45,870 $ 47,769 Income taxes paid, net $ 46,734 $ 735 * AFUDC - borrowed was $816,000 and $1.3 million for the six months ended June 30, 2021 and 2020, respectively. Noncash investing and financing transactions were as follows: June 30, 2021 June 30, 2020 December 31, 2020 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 17,224 $ 24,181 $ 54,356 Property, plant and equipment additions in accounts payable $ 31,886 $ 36,493 $ 26,082 Accrual for holdback payment related to a business combination $ — $ 5,000 $ 2,500

Business segment data (Tables)

Business segment data (Tables)	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
Information on the Company's businesses	Information on the Company's segments was as follows: Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (In thousands) External operating revenues: Regulated operations: Electric $ 83,650 $ 76,438 $ 168,324 $ 162,346 Natural gas distribution 153,788 141,494 503,994 467,937 Pipeline 23,130 23,421 30,633 29,752 260,568 241,353 702,951 660,035 Non-regulated operations: Pipeline 4,643 4,237 7,052 8,561 Construction materials and contracting 633,674 621,045 899,333 883,190 Construction services 524,744 496,405 1,042,214 1,008,610 Other 28 (112) 45 (94) 1,163,089 1,121,575 1,948,644 1,900,267 Total external operating revenues $ 1,423,657 $ 1,362,928 $ 2,651,595 $ 2,560,302 Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (In thousands) Intersegment operating revenues: Regulated operations: Electric $ 136 $ 196 $ 271 $ 391 Natural gas distribution 142 185 284 370 Pipeline 7,695 7,857 33,685 33,040 7,973 8,238 34,240 33,801 Non-regulated operations: Pipeline 167 142 407 158 Construction materials and contracting 142 90 204 152 Construction services 797 779 1,839 3,249 Other 3,361 2,973 6,685 5,946 4,467 3,984 9,135 9,505 Intersegment eliminations (12,440) (12,222) (43,375) (43,306) Total intersegment operating revenues $ — $ — $ — $ — Operating income (loss): Electric $ 12,806 $ 12,810 $ 26,672 $ 27,669 Natural gas distribution 3,601 678 57,173 50,677 Pipeline 11,076 12,225 23,612 23,644 Construction materials and contracting 72,452 74,741 37,563 31,472 Construction services 37,774 37,882 78,051 61,678 Other (20) (82) (218) 185 Total operating income $ 137,689 $ 138,254 $ 222,853 $ 195,325 Net income (loss): Regulated operations: Electric $ 10,304 $ 12,153 $ 21,054 $ 23,527 Natural gas distribution (707) (959) 35,471 31,410 Pipeline 8,089 8,684 17,283 16,070 17,686 19,878 73,808 71,007 Non-regulated operations: Pipeline 1,106 268 810 255 Construction materials and contracting 51,396 53,020 20,584 14,806 Construction services 28,885 27,932 58,709 44,755 Other 1,098 (1,256) (1,624) (5,442) 82,485 79,964 78,479 54,374 Income from continuing operations 100,171 99,842 152,287 125,381 Income (loss) from discontinued operations, net of tax 19 (139) 34 (548) Net income $ 100,190 $ 99,703 $ 152,321 $ 124,833

Employee benefit plans (Tables)

Employee benefit plans (Tables)	6 Months Ended
	Jun. 30, 2021
Retirement Benefits [Abstract]
Schedule of net benefit costs	Components of net periodic benefit credit for the Company's pension and other postretirement benefit plans were as follows: Pension Benefits Other Three Months Ended June 30, 2021 2020 2021 2020 (In thousands) Components of net periodic benefit credit: Service cost $ — $ — $ 400 $ 414 Interest cost 2,455 3,074 466 627 Expected return on assets (4,894) (5,214) (1,275) (1,401) Amortization of prior service credit — — (349) (402) Amortization of net actuarial loss 2,004 1,723 6 142 Net periodic benefit credit, including amount capitalized (435) (417) (752) (620) Less amount capitalized — — 44 35 Net periodic benefit credit $ (435) $ (417) $ (796) $ (655) Pension Benefits Other Six Months Ended June 30, 2021 2020 2021 2020 (In thousands) Components of net periodic benefit credit: Service cost $ — $ — $ 800 $ 766 Interest cost 4,910 6,047 932 1,218 Expected return on assets (9,788) (9,975) (2,550) (2,649) Amortization of prior service credit — — (698) (699) Amortization of net actuarial loss 4,008 3,586 12 144 Net periodic benefit credit, including amount capitalized (870) (342) (1,504) (1,220) Less amount capitalized — — 83 67 Net periodic benefit credit $ (870) $ (342) $ (1,587) $ (1,287)

Receivables and allowance for_3

Receivables and allowance for expected credit losses (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Credit Loss [Abstract]
Accounts Receivable, Noncurrent, 90 Days or More Past Due, Still Accruing	$ 34.2	$ 43.9	$ 45.1

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
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	$ 12,714	$ 15,358	$ 11,125	$ 8,497
Current expected credit loss provision	(841)	(317)	1,075	3,555
Less write-offs charged against the allowance	1,424	2,669	1,399	1,265
Credit loss recoveries collected	299	342	289	338
Balance	10,748	12,714	11,090	11,125
Electric
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	678	899	492	328
Current expected credit loss provision	(110)	538	303	555
Less write-offs charged against the allowance	341	888	224	500
Credit loss recoveries collected	100	129	88	109
Balance	327	678	659	492
Natural gas distribution
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	2,950	2,571	1,817	1,056
Current expected credit loss provision	(103)	1,273	190	1,156
Less write-offs charged against the allowance	787	1,107	677	624
Credit loss recoveries collected	199	213	201	229
Balance	2,259	2,950	1,531	1,817
Pipeline
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	2	2	0	0
Current expected credit loss provision	0	0	0	0
Less write-offs charged against the allowance	0	0	0	0
Credit loss recoveries collected	0	0	0	0
Balance	2	2	0	0
Construction materials and contracting
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	4,842	6,164	5,983	5,357
Current expected credit loss provision	11	(1,049)	(314)	694
Less write-offs charged against the allowance	232	273	44	68
Credit loss recoveries collected	0	0	0	0
Balance	4,621	4,842	5,625	5,983
Construction services
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	4,242	5,722	2,833	1,756
Current expected credit loss provision	(639)	(1,079)	896	1,150
Less write-offs charged against the allowance	64	401	454	73
Credit loss recoveries collected	0	0	0	0
Balance	$ 3,539	$ 4,242	$ 3,275	$ 2,833

Inventories and natural gas i_4

Inventories and natural gas in storage (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Inventory Disclosure [Abstract]
Aggregates held for resale	$ 183,977	$ 175,782	$ 165,357
Asphalt oil	51,500	28,238	57,207
Materials and supplies	27,969	25,142	27,805
Merchandise for resale	26,871	21,087	22,974
Natural gas in storage (current)	10,824	21,919	11,776
Other	15,187	18,999	17,718
Total	316,328	291,167	302,837
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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	201,345	200,522	201,028	200,481
Effect of dilutive performance share awards and restricted stock units	348	17	300	16
Weighted average common shares outstanding - diluted	201,693	200,539	201,328	200,497
Shares excluded from the calculation of diluted earnings per share	0	187	0	191
Dividends declared per common share	$ 0.2125	$ 0.2075	$ 0.4250	$ 0.4150

Equity (Details)

Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Class of Stock [Line Items]
Common Stock, Shares Authorized	500,000,000	500,000,000	500,000,000	500,000,000	500,000,000
Proceeds from issuance of common stock			$ 54,649	$ 3,410
At-the-market offering
Class of Stock [Line Items]
Common Stock, Shares Authorized	6,400,000		6,400,000
Common Stock, Capital Shares Reserved for Future Issuance	4,600,000		4,600,000
Issuance of common stock (shares)	1,100,000	0	1,800,000	0
Proceeds from issuance of common stock	$ 34,900	$ 0	$ 54,600	$ 0
Payments of Stock Issuance Costs	$ 400	$ 0	$ 700	$ 0

Accumulated other comprehensi_3

Accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	$ 3,100,306	$ 3,079,105	$ 2,836,592	$ 2,847,246	$ 3,079,105	$ 2,847,246
Other comprehensive income (loss)	542	568	586	707	1,110	1,293
Balance	3,198,802	3,100,306	2,897,687	2,836,592	3,198,802	2,897,687
Net unrealized gain (loss) on derivative instruments qualifying as hedges
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(873)	(984)	(1,319)	(1,430)	(984)	(1,430)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from (to) accumulated other comprehensive loss	112	111	112	111
Other comprehensive income (loss)	112	111	112	111
Balance	(761)	(873)	(1,207)	(1,319)	(761)	(1,207)
Postretirement liability adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(46,741)	(47,207)	(40,272)	(40,734)	(47,207)	(40,734)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from (to) accumulated other comprehensive loss	457	466	480	462
Other comprehensive income (loss)	457	466	480	462
Balance	(46,284)	(46,741)	(39,792)	(40,272)	(46,284)	(39,792)
Net unrealized gain (loss) on available-for-sale investments
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	104	113	196	62	113	62
Other comprehensive income (loss) before reclassifications	(52)	(44)	(13)	135
Amounts reclassified from (to) accumulated other comprehensive loss	25	35	7	(1)
Other comprehensive income (loss)	(27)	(9)	(6)	134
Balance	77	104	190	196	77	190
Total accumulated other comprehensive loss
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(47,510)	(48,078)	(41,395)	(42,102)	(48,078)	(42,102)
Other comprehensive income (loss) before reclassifications	(52)	(44)	(13)	135
Amounts reclassified from (to) accumulated other comprehensive loss	594	612	599	572
Other comprehensive income (loss)	542	568	586	707
Balance	$ (46,968)	$ (47,510)	$ (40,809)	$ (41,395)	$ (46,968)	$ (40,809)

Reclassification out of accumul

Reclassification out of accumulated other comprehensive loss (Details 2) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Interest expense	$ (23,381)		$ (24,818)		$ (46,835)	$ (49,371)
Income taxes	(23,164)		(23,657)		(36,112)	(29,631)
Other income	9,027		10,063		12,381	9,058
Net Income	100,190	$ 52,131	99,703	$ 25,130	152,321	124,833
Reclassification out of accumulated other comprehensive loss
Reclassification adjustment out of accumulated other comprehensive loss [Line Items]
Net Income	(594)		(599)		(1,206)	(1,171)
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)		(148)		(296)	(295)
Income taxes	36		36		73	72
Net Income	(112)		(112)		(223)	(223)
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	160		155		311	304
Other income	(617)		(635)		(1,234)	(1,246)
Net Income	(457)		(480)		(923)	(942)
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	6		2		15	2
Other income	(31)		(9)		(75)	(8)
Net Income	$ (25)		$ (7)		$ (60)	$ (6)

Disaggregation of revenue (Deta

Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Operating revenues:	$ 1,423,657	$ 1,362,928	$ 2,651,595	$ 2,560,302
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(12,440)	(12,222)	(43,375)	(43,306)
Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(145,780)	(164,719)	(192,496)	(208,823)
Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	39,136	38,315	81,005	77,545
Natural gas gathering
Disaggregation of Revenue [Line Items]
Operating revenues:		1,181		3,271
Natural gas storage
Disaggregation of Revenue [Line Items]
Operating revenues:	3,094	3,104	7,123	6,150
Contracting services
Disaggregation of Revenue [Line Items]
Operating revenues:	280,834	303,356	376,859	401,757
Construction materials
Disaggregation of Revenue [Line Items]
Operating revenues:	498,762	482,498	715,174	690,408
Inside specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	347,702	324,921	702,892	697,130
Outside specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	165,123	160,696	316,486	290,846
Other
Disaggregation of Revenue [Line Items]
Operating revenues:	20,515	17,064	39,334	34,595
Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	1,409,489	1,347,026	2,625,505	2,530,574
Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	14,168	15,902	26,090	29,728
Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	112,738	106,607	349,311	325,657
Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	81,446	70,904	234,426	219,487
Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	16,534	13,730	35,375	32,618
Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	1,825	1,591	3,391	3,239
Electric
Disaggregation of Revenue [Line Items]
Operating revenues:	83,650	76,438	168,324	162,346
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(136)	(196)	(271)	(391)
Electric | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	9,465	7,717	19,238	16,167
Electric | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	84,600	75,015	172,197	161,221
Electric | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	(950)	1,423	(3,873)	1,125
Electric | Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	29,258	27,954	62,694	60,303
Electric | Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	33,834	29,877	66,762	63,464
Electric | Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	10,354	8,072	20,383	18,439
Electric | Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	1,825	1,591	3,391	3,239
Natural gas distribution
Disaggregation of Revenue [Line Items]
Operating revenues:	153,788	141,494	503,994	467,937
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(142)	(185)	(284)	(370)
Natural gas distribution | Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	11,451	10,350	23,903	22,148
Natural gas distribution | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	2,794	2,711	5,803	5,209
Natural gas distribution | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	151,375	138,214	498,695	462,543
Natural gas distribution | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	2,413	3,280	5,299	5,394
Natural gas distribution | Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	83,480	78,653	286,617	265,354
Natural gas distribution | Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	47,612	41,027	167,664	156,023
Natural gas distribution | Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	6,180	5,658	14,992	14,179
Natural gas distribution | Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0	0	0
Pipeline
Disaggregation of Revenue [Line Items]
Operating revenues:	27,773	27,658	37,685	38,313
Pipeline | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(7,862)	(7,999)	(34,092)	(33,198)
Pipeline | Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	27,685	27,965	57,102	55,397
Pipeline | Natural gas gathering
Disaggregation of Revenue [Line Items]
Operating revenues:		1,181		3,271
Pipeline | Natural gas storage
Disaggregation of Revenue [Line Items]
Operating revenues:	3,094	3,104	7,123	6,150
Pipeline | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	4,810	3,363	7,470	6,604
Pipeline | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	27,727	27,614	37,603	38,224
Pipeline | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	46	44	82	89
Construction materials and contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	633,674	621,045	899,333	883,190
Construction materials and contracting | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(142)	(90)	(204)	(152)
Construction materials and contracting | Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(145,780)	(164,719)	(192,496)	(208,823)
Construction materials and contracting | Contracting services
Disaggregation of Revenue [Line Items]
Operating revenues:	280,834	303,356	376,859	401,757
Construction materials and contracting | Construction materials
Disaggregation of Revenue [Line Items]
Operating revenues:	498,762	482,498	715,174	690,408
Construction materials and contracting | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0	0	0
Construction materials and contracting | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	633,674	621,045	899,333	883,190
Construction materials and contracting | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0	0	0
Construction services
Disaggregation of Revenue [Line Items]
Operating revenues:	524,744	496,405	1,042,214	1,008,610
Construction services | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(797)	(779)	(1,839)	(3,249)
Construction services | Inside specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	347,702	324,921	702,892	697,130
Construction services | Outside specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	165,123	160,696	316,486	290,846
Construction services | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	57	412	93	763
Construction services | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	512,085	485,250	1,017,632	985,490
Construction services | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	12,659	11,155	24,582	23,120
Other
Disaggregation of Revenue [Line Items]
Operating revenues:	28	(112)	45	(94)
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(3,361)	(2,973)	(6,685)	(5,946)
Other | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	3,389	2,861	6,730	5,852
Other | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	28	(112)	45	(94)
Other | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	$ 0	$ 0	$ 0	$ 0

Contract balances (Details 2)

Contract balances (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Contract assets	$ 147,033		$ 147,033		$ 104,345
Change in contract assets			42,688
Contract liabilities - current	(146,116)		(146,116)		(158,603)
Change in contract liabilities - current			12,487
Contract liabilities - noncurrent	(160)		(160)		(52)
Change in contract liabilities - noncurrent			(108)
Net contract assets (liabilities)	757		757		$ (54,310)
Change in net contract liabilities			55,067
Amounts included in contract liability at the beginning of the period	21,900	$ 32,300	145,300	$ 121,700
Amounts from performance obligations satisfied in prior periods	$ 27,300	$ 31,900	$ 54,600	$ 42,900

Revenue from contracts with c_4

Revenue from contracts with customers Remaining performance obligations (Details 3) $ in Millions	Jun. 30, 2021USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 2,400
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 1,800
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 339.5
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	13 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 225.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	25 months

Business Combinations (Details)

Business Combinations (Details) - USD ($)	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill	$ 717,863,000	$ 714,963,000	$ 708,664,000	$ 681,358,000
2021 Acquisition
Business Acquisition [Line Items]
Gross Aggregate Consideration	13,800,000
Cash Assumed	100,000
Business Combination, Consideration Transferred	13,700,000
Current Assets	700,000
Property, Plant, and Equipment	13,000,000
Goodwill	2,900,000
Other Intangibles	600,000
Current Liabilities	200,000
Deferred Credits and Other Liabilities	100,000
Deferred Tax Liabilities	$ 3,200,000

Business Combinations (Details

Business Combinations (Details 2) - USD ($)	12 Months Ended
	Dec. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill	$ 714,963,000	$ 717,863,000	$ 708,664,000	$ 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, Consideration Transferred, Liabilities Incurred	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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Leases [Abstract]
Operating Lease, Lease Income	$ 12.8	$ 11.2	$ 24.8	$ 23.3
Lessor, Operating Lease, Payments to be Received, Next Twelve Months	$ 9.8		$ 9.8

Goodwill rollforward (Details)

Goodwill rollforward (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Goodwill [Roll Forward]
Balance at beginning of period	$ 714,963	$ 681,358	$ 681,358
Goodwill acquired during the year	2,900	30,919	33,214
Measurement period adjustments	0	(3,613)	391
Balance at end of period	717,863	708,664	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	2,900	6,483	8,778
Measurement period adjustments	0	0	(9)
Balance at end of period	228,903	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	24,436	24,436
Measurement period adjustments	0	(3,613)	400
Balance at end of period	$ 143,224	$ 139,211	$ 143,224

Other intangible assets (Detail

Other intangible assets (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 23,401	$ 31,515	$ 23,401	$ 31,515	$ 25,496
Amortization of intangible assets	1,200	2,700	2,700	4,700
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	29,423	30,087	29,423	30,087	28,836
Intangible assets, less accumulated amortization	8,765	5,239	8,765	5,239	6,887
Intangible assets, net (excluding goodwill)	20,658	24,848	20,658	24,848	21,949
Noncompete agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	3,991	4,229	3,991	4,229	3,941
Intangible assets, less accumulated amortization	2,576	2,084	2,576	2,084	2,309
Intangible assets, net (excluding goodwill)	1,415	2,145	1,415	2,145	1,632
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	11,957	13,060	11,957	13,060	12,927
Intangible assets, less accumulated amortization	10,629	8,538	10,629	8,538	11,012
Intangible assets, net (excluding goodwill)	$ 1,328	$ 4,522	$ 1,328	$ 4,522	$ 1,915

Future amortization expense (De

Future amortization expense (Details 3) $ in Thousands	Jun. 30, 2021USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Remainder of 2021	$ 2,381
2022	4,678
2023	4,329
2024	3,957
2025	2,060
Thereafter	$ 5,996

Regulatory assets (Details)

Regulatory assets (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Feb. 28, 2021	Dec. 31, 2020	Jun. 30, 2020
Regulatory Assets
Regulatory Assets, Current	$ 109,581		$ 68,527	$ 60,557
Regulatory Assets, Noncurrent	376,913		379,381	351,025
Total regulatory assets	486,494		447,908	411,582
Regulatory assets not earning a rate of return	317,000		332,500	296,600
Natural gas costs recoverable through rate adjustments
Regulatory Assets
Regulatory Assets, Current	85,045		42,481	42,582
Regulatory Assets, Noncurrent	$ 8,389		21,539	27,184
Natural gas costs recoverable through rate adjustments | Minimum [Member]
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	Up to 1 year
Natural gas costs recoverable through rate adjustments | Maximum [Member]
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	Up to 3 years
Conservation programs
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	Up to 1 year
Regulatory Assets, Current	$ 7,580		7,117	7,256
Cost recovery mechanisms
Regulatory Assets
Regulatory Assets, Current	5,692		10,645	7,781
Regulatory Assets, Noncurrent	$ 44,415		16,245	13,140
Cost recovery mechanisms | Minimum [Member]
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	Up to 1 year
Cost recovery mechanisms | Maximum [Member]
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	Up to 10 years
Pension and postretirement benefits
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	**
Regulatory Assets, Noncurrent	$ 155,906		155,942	157,033
Plant costs/asset retirement obligations
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	Over plant lives
Regulatory Assets, Noncurrent	$ 72,853		71,740	68,191
Plant retirement
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	-
Regulatory Assets, Noncurrent	$ 46,061		65,919	49,185
Manufactured gas plant site remediation
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	-
Regulatory Assets, Noncurrent	$ 26,155		26,429	14,826
Taxes recoverable from/refundable to customers
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	Over plant lives
Regulatory Assets, Noncurrent	$ 10,929		10,785	10,890
Long-term debt refinancing costs
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	Up to 39 years
Regulatory Assets, Noncurrent	$ 4,110		4,426	3,980
Other regulatory assets/liabilities
Regulatory Assets
Regulatory Assets, Current	11,264		8,284	2,938
Regulatory Assets, Noncurrent	$ 8,095		$ 6,356	$ 6,596
Other regulatory assets/liabilities | Minimum [Member]
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	Up to 1 year
Other regulatory assets/liabilities | Maximum [Member]
Regulatory Assets
Estimated Recovery or Refund Period as of June 30, 2021	Up to 18 years
Increased Gas Costs
Regulatory Assets
Total regulatory assets		$ 44,000

Regulatory liabilities (Details

Regulatory liabilities (Details 2) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	$ 23,454	$ 31,450	$ 48,000
Regulatory liabilities	428,467	428,075	438,652
Total regulatory liabilities	451,921	459,525	486,652
Net regulatory position	$ 34,573	(11,617)	(75,070)
Natural gas costs refundable through rate adjustments
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2021	Up to 1 year
Regulatory liabilities due within one year	$ 8,935	18,565	29,557
Electric fuel and purchased power deferral
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2021	Up to 1 year
Regulatory liabilities due within one year	$ 5,431	3,667	7,799
Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	3,434	3,557	4,012
Regulatory liabilities	$ 222,098	227,850	236,142
Deferred Income Tax Charge [Member] | Minimum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2021	Up to 1 year
Deferred Income Tax Charge [Member] | Maximum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2021	Over plant lives
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Regulatory liabilities due within one year	$ 5,654	5,661	6,632
Regulatory liabilities	$ 18,048	16,065	11,096
Other Regulatory Liabilities | Minimum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2021	Up to 1 year
Other Regulatory Liabilities | Maximum [Member]
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2021	Up to 21 years
Plant retirement
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2021	Over plant lives
Regulatory liabilities	$ 171,381	167,171	173,399
Pension and postretirement benefits
Regulatory Liabilities [Line Items]
Estimated Recovery or Refund Period as of June 30, 2021	**
Regulatory liabilities	$ 16,940	$ 16,989	$ 18,015

Fair value measurements Insuran

Fair value measurements Insurance contracts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Investments used to satisfy nonqualified benefit plans obligations	$ 105.7	$ 92.4	$ 105.7	$ 92.4	$ 100.1
Net unrealized gain on investments used to satisfy obligations under nonqualified benefit plans	$ 3.8	$ 9.1	$ 3.9	$ 5.4

Available-for-sale securities (

Available-for-sale securities (Details 2) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Available-for-sale securities [Abstract]
Cost	$ 11,171	$ 11,185	$ 10,982
Gross Unrealized Gains	127	156	246
Gross Unrealized Losses	30	14	6
Fair Value	11,268	11,327	11,222
Mortgage-backed securities
Available-for-sale securities [Abstract]
Cost	8,278	9,799	9,812
Gross Unrealized Gains	127	156	239
Gross Unrealized Losses	9	9	6
Fair Value	8,396	9,946	10,045
U.S. Treasury securities
Available-for-sale securities [Abstract]
Cost	2,893	1,386	1,170
Gross Unrealized Gains	0	0	7
Gross Unrealized Losses	21	5	0
Fair Value	$ 2,872	$ 1,381	$ 1,177

Fair value measurements (Detail

Fair value measurements (Details 3) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Concentration risks, percentage [Abstract]
Percentage in fixed-income and other investments	53.00%	57.00%	38.00%
Percentage investment in common stock of large-cap companies	20.00%	18.00%	23.00%
Percentage investment in common stock of mid-cap companies	10.00%	9.00%	9.00%
Percentage investment in common stock of small-cap companies	9.00%	9.00%	9.00%
Percentage investment in target date investments	6.00%	5.00%	4.00%
Percentage investment in cash and cash equivalents	2.00%	2.00%	17.00%
Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 129,186	$ 120,348	$ 112,113
Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	129,186	120,348	112,113
Money market funds | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	12,234	8,917	8,478
Money market funds | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	12,234	8,917	8,478
Insurance contracts* | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	105,684	100,104	92,413
Insurance contracts* | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	105,684	100,104	92,413
Mortgage-backed securities | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	8,396	9,946	10,045
Mortgage-backed securities | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	8,396	9,946	10,045
U.S. Treasury securities | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	2,872	1,381	1,177
U.S. Treasury securities | Fair value, inputs, level 2 | Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 2,872	$ 1,381	$ 1,177

Fair value measurements (Deta_2

Fair value measurements (Details 4) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Fair value, balance sheet grouping [Line Items]
Long-term debt	$ 2,337,049	$ 2,213,130	$ 2,281,876
Carrying amount
Fair value, balance sheet grouping [Line Items]
Long-term debt	2,337,049	2,213,130	2,281,876
Fair value
Fair value, balance sheet grouping [Line Items]
Long-term debt, fair value	$ 2,616,232	$ 2,537,289	$ 2,563,734

Long-term debt outstanding (Det

Long-term debt outstanding (Details 1) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Long-term debt outstanding [Line Items]
Long-term debt	$ 2,337,049	$ 2,213,130	$ 2,281,876
Long-term debt due within one year	1,549	1,555	16,560
Long-term debt	$ 2,335,500	2,211,575	2,265,316
Senior Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	4.40%
Long-term debt	$ 1,950,000	1,950,000	1,900,000
Commercial Paper
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	0.32%
Long-term debt	$ 297,400	125,600	290,100
Credit Agreements
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	3.25%
Long-term debt	$ 48,550	95,900	11,200
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	0.83%
Long-term debt	$ 3,232	4,034	28,342
Long-term Debt
Long-term debt outstanding [Line Items]
Unamortized Debt Issuance Costs	5,505	5,803	6,668
Discount	$ 28	$ 1	$ 198

Schedule of debt maturities (De

Schedule of debt maturities (Details 2) $ in Thousands	Jun. 30, 2021USD ($)
Long-term debt maturities [Line Items]
Remainder of 2021	$ 752
2022	148,021
2023	77,921
2024	407,372
2025	177,802
Thereafter	$ 1,530,714

Cash flow information (Details)

Cash flow information (Details) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Supplemental Cash Flow Information [Abstract]
Interest, net*	$ 45,870,000	$ 47,769,000
Income taxes paid, net	46,734,000	735,000
AFUDC borrowed	816,000	1,300,000
Right-of-use assets obtained in exchange for new operating lease liabilities	17,224,000	24,181,000	$ 54,356,000
Property, plant and equipment additions in accounts payable	31,886,000	36,493,000	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				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 1,423,657		$ 1,362,928		$ 2,651,595	$ 2,560,302
Operating income	137,689		138,254		222,853	195,325
Income from continuing operations	100,171		99,842		152,287	125,381
Income (loss) from discontinued operations, net of tax	19		(139)		34	(548)
Net income	100,190	$ 52,131	99,703	$ 25,130	152,321	124,833
Electric
Segment Reporting Information [Line Items]
Revenues	83,650		76,438		168,324	162,346
Operating income	12,806		12,810		26,672	27,669
Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	153,788		141,494		503,994	467,937
Operating income	3,601		678		57,173	50,677
Pipeline
Segment Reporting Information [Line Items]
Revenues	27,773		27,658		37,685	38,313
Operating income	11,076		12,225		23,612	23,644
Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	633,674		621,045		899,333	883,190
Operating income	72,452		74,741		37,563	31,472
Construction services
Segment Reporting Information [Line Items]
Revenues	524,744		496,405		1,042,214	1,008,610
Operating income	37,774		37,882		78,051	61,678
Other
Segment Reporting Information [Line Items]
Revenues	28		(112)		45	(94)
Operating income	(20)		(82)		(218)	185
Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(12,440)		(12,222)		(43,375)	(43,306)
Intersegment eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	(136)		(196)		(271)	(391)
Intersegment eliminations | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	(142)		(185)		(284)	(370)
Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	(7,862)		(7,999)		(34,092)	(33,198)
Intersegment eliminations | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	(142)		(90)		(204)	(152)
Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	(797)		(779)		(1,839)	(3,249)
Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	(3,361)		(2,973)		(6,685)	(5,946)
Total intersegment operating revenues
Segment Reporting Information [Line Items]
Revenues	0		0		0	0
Regulated operation
Segment Reporting Information [Line Items]
Revenues	260,568		241,353		702,951	660,035
Income from continuing operations	17,686		19,878		73,808	71,007
Regulated operation | Electric
Segment Reporting Information [Line Items]
Revenues	83,650		76,438		168,324	162,346
Income from continuing operations	10,304		12,153		21,054	23,527
Regulated operation | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	153,788		141,494		503,994	467,937
Income from continuing operations	(707)		(959)		35,471	31,410
Regulated operation | Pipeline
Segment Reporting Information [Line Items]
Revenues	23,130		23,421		30,633	29,752
Income from continuing operations	8,089		8,684		17,283	16,070
Regulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	7,973		8,238		34,240	33,801
Regulated operation | Intersegment eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	136		196		271	391
Regulated operation | Intersegment eliminations | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	142		185		284	370
Regulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	7,695		7,857		33,685	33,040
Nonregulated operation
Segment Reporting Information [Line Items]
Revenues	1,163,089		1,121,575		1,948,644	1,900,267
Income from continuing operations	82,485		79,964		78,479	54,374
Nonregulated operation | Pipeline
Segment Reporting Information [Line Items]
Revenues	4,643		4,237		7,052	8,561
Income from continuing operations	1,106		268		810	255
Nonregulated operation | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	633,674		621,045		899,333	883,190
Income from continuing operations	51,396		53,020		20,584	14,806
Nonregulated operation | Construction services
Segment Reporting Information [Line Items]
Revenues	524,744		496,405		1,042,214	1,008,610
Income from continuing operations	28,885		27,932		58,709	44,755
Nonregulated operation | Other
Segment Reporting Information [Line Items]
Revenues	28		(112)		45	(94)
Income from continuing operations	1,098		(1,256)		(1,624)	(5,442)
Nonregulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	4,467		3,984		9,135	9,505
Nonregulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	167		142		407	158
Nonregulated operation | Intersegment eliminations | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	142		90		204	152
Nonregulated operation | Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	797		779		1,839	3,249
Nonregulated operation | Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	$ 3,361		$ 2,973		$ 6,685	$ 5,946

Employee benefit plans (Details

Employee benefit plans (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Qualified plan | Underfunded plan | Pension benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	2,455,000	3,074,000	4,910,000	6,047,000
Expected return on assets	(4,894,000)	(5,214,000)	(9,788,000)	(9,975,000)
Amortization of prior service credit	0	0	0	0
Amortization of net actuarial loss	2,004,000	1,723,000	4,008,000	3,586,000
Net periodic benefit credit, including amount capitalized	(435,000)	(417,000)	(870,000)	(342,000)
Less amount capitalized	0	0	0	0
Net periodic benefit credit	(435,000)	(417,000)	(870,000)	(342,000)
Qualified plan | Overfunded Plan | Other postretirement benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	400,000	414,000	800,000	766,000
Interest cost	466,000	627,000	932,000	1,218,000
Expected return on assets	(1,275,000)	(1,401,000)	(2,550,000)	(2,649,000)
Amortization of prior service credit	(349,000)	(402,000)	(698,000)	(699,000)
Amortization of net actuarial loss	6,000	142,000	12,000	144,000
Net periodic benefit credit, including amount capitalized	(752,000)	(620,000)	(1,504,000)	(1,220,000)
Less amount capitalized	44,000	35,000	83,000	67,000
Net periodic benefit credit	(796,000)	(655,000)	(1,587,000)	(1,287,000)
Nonqualified plan | Unfunded plan | Supplemental employee retirement plans
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Net periodic benefit credit	$ 769,000	$ 900,000	$ 1,500,000	$ 1,900,000

IPUC (Details)

IPUC (Details) - Pending Rate Case [Member] - IPUC - Intermountain Gas - Gas Distribution [Member] - USD ($) $ in Millions	Jun. 03, 2021	Jan. 12, 2021
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%
Depreciation and Amortization Requested Rate Increase (Decrease), Amended Amount	$ (3.8)
Depreciation and Amortization, Requested Rate, Amended, Percent	2.40%

MNPUC (Details 2)

MNPUC (Details 2) $ in Millions	Mar. 30, 2021USD ($)
MNPUC [Member] | Gas Distribution [Member] | Great Plains Natural Gas Co. [Member] | Pending Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 11.1

NDPSC (Details 3)

NDPSC (Details 3) - NDPSC [Member] - Montana-Dakota Utilities Co. [Member] - USD ($) $ in Millions	Jul. 15, 2021	Jun. 01, 2021
Gas Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 13.5
Pending Rate Case [Member] | Electric | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Total Transmission Cost Adjustment Rider	$ 14.5
Public Utilities, Requested Rate Increase (Decrease), Amount	(1.1)
Transmission Capital Projects Increase (Decrease)	$ 5.1

SDPUC (Details 4)

SDPUC (Details 4)	Mar. 11, 2021USD ($)
SDPUC | Pending Rate Case [Member] | Electricity [Member] | Montana-Dakota Utilities Co. [Member]
Public Utilities, General Disclosures [Line Items]
Total Infrastructure Rider	$ 0

WUTC (Details 5)

WUTC (Details 5) - WUTC [Member] - Cascade Natural Gas [Member] - USD ($)	Jul. 01, 2021	Jun. 01, 2021	Jan. 08, 2021	Jul. 24, 2020	Jun. 19, 2020
Gas Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 13,800,000
Public Utilities, Requested Rate Increase (Decrease), Percentage					5.30%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 7,400,000	$ 14,300,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage			2.80%	5.50%
Gas Distribution [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ (391,000)
Public Utilities, Approved Rate Increase (Decrease), Percentage	(0.20%)
Pending Rate Case [Member] | Pipeline Cost Recovery Mechanism [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 2,100,000
Public Utilities, Requested Rate Increase (Decrease), Percentage		0.80%

Litigation (Details)

Litigation (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Loss Contingencies [Line Items]
Potential liabilities related to litigation and environmental matters	$ 30.8	$ 41.5	$ 34.5
Insurance Receivable	6.9	17.5	21.1
Regulatory Assets	$ 21.2	$ 21.3	$ 10.4

Guarantees (Details 2)

Guarantees (Details 2)	Jun. 30, 2021USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 171,200,000
Fixed maximum amounts guaranteed by year 2021	37,200,000
Fixed maximum amounts guaranteed by year 2022	67,700,000
Fixed maximum amounts guaranteed by year 2023	55,600,000
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	23,400,000
Letters of credit set to expire - 2022	2,100,000
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	Jun. 30, 2021USD ($)
Fuel contract
Variable Interest Entities [Line Items]
Variable interest entity, reporting entity involvement, maximum loss exposure, amount	$ 32.6