MDU Resources (MDU) 10-Q 5 Nov 20 2020 Q3 Quarterly report Financial data

Cover page

Cover page - shares	9 Months Ended
	Sep. 30, 2020	Oct. 29, 2020
Document Information [Line Items]
Document type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
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		200,522,277
Entity Central Index Key	0000067716
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating revenues:
Operating revenues:	$ 1,587,289	$ 1,563,799	$ 4,147,591	$ 3,958,563
Operating expenses:
Operation and maintenance:	1,214,019	1,212,620	3,064,189	2,936,564
Purchased natural gas sold	31,524	31,843	253,780	270,539
Depreciation, depletion and amortization	72,084	65,021	212,832	187,937
Taxes, other than income	50,501	46,128	167,197	148,110
Electric fuel and purchased power	15,450	18,717	50,557	64,413
Total operating expenses	1,383,578	1,374,329	3,748,555	3,607,563
Operating income	203,711	189,470	399,036	351,000
Other income	4,612	3,014	13,669	12,222
Interest expense	23,761	25,258	73,132	74,094
Income before income taxes	184,562	167,226	339,573	289,128
Income taxes	31,547	31,098	61,178	48,766
Income from continuing operations	153,015	136,128	278,395	240,362
Income (loss) from discontinued operations, net of tax	63	1,509	(484)	26
Net income	$ 153,078	$ 137,637	$ 277,911	$ 240,388
Earnings per share - basic:
Income from continuing operations	$ 0.76	$ 0.68	$ 1.39	$ 1.21
Discontinued operations, net of tax	0	0.01	0	0
Earnings per share - basic	0.76	0.69	1.39	1.21
Earnings per share - diluted:
Income from continuing operations	0.76	0.68	1.39	1.21
Discontinued operations, net of tax	0	0.01	0	0
Earnings per share - diluted	$ 0.76	$ 0.69	$ 1.39	$ 1.21
Weighted average common shares outstanding - basic	200,522	199,343	200,495	198,016
Weighted average common shares outstanding - diluted	200,619	199,383	200,515	198,033
Regulated operation
Operating revenues:
Operating revenues:	$ 210,115	$ 209,444	$ 870,151	$ 885,309
Operating expenses:
Operation and maintenance:	89,080	86,249	259,791	262,434
Income from continuing operations	6,985	7,599	77,991	74,206
Nonregulated operation
Operating revenues:
Operating revenues:	1,377,174	1,354,355	3,277,440	3,073,254
Operating expenses:
Operation and maintenance:	1,124,939	1,126,371	2,804,398	2,674,130
Income from continuing operations	$ 146,030	$ 128,529	$ 200,404	$ 166,156

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net income	$ 153,078	$ 137,637	$ 277,911	$ 240,388
Other comprehensive income:
Reclassification adjustment for loss on derivative instruments included in net income, tax	37	36	109	(177)
Reclassification adjustment for loss on derivative instruments included in net income, net of tax	111	112	334	620
Postretirement liability adjustment:
Amortization of postretirement liability losses included in net periodic benefit cost, tax	152	95	456	284
Amortization of postretirement liability losses included in net periodic benefit cost, net of tax	471	292	1,413	878
Net unrealized gain (loss) on available-for-sale investments:
Net unrealized gain (loss) on available-for-sale investments arising during the period, tax	(13)	3	19	35
Net unrealized gain (loss) on available-for-sale investments arising during the period, net of tax	(50)	12	72	130
Reclassification adjustment for (gain) loss on available-for-sale investments included in net income, tax	7	(1)	9	10
Reclassification adjustment for (gain) loss on available-for-sale investments included in net income, net of tax	28	(4)	34	36
Net unrealized gain (loss) on available-for-sale investments	(22)	8	106	166
Other comprehensive income	560	412	1,853	1,664
Comprehensive income attributable to common stockholders	$ 153,638	$ 138,049	$ 279,764	$ 242,052

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Current assets:
Cash and cash equivalents	$ 66,070	$ 66,459	$ 67,000
Receivables, net	1,009,433	836,605	968,279
Inventories	286,223	278,407	286,057
Current regulatory assets	79,125	63,613	69,181
Prepayments and other current assets	61,706	52,617	71,298
Total current assets	1,502,557	1,297,701	1,461,815
Noncurrent assets:
Property, plant and equipment	8,203,751	7,908,628	7,746,754
Less accumulated depreciation, depletion and amortization	3,115,805	2,991,486	2,944,928
Net property, plant and equipment	5,087,946	4,917,142	4,801,826
Goodwill	712,677	681,358	681,349
Other intangible assets, net	26,376	15,246	15,511
Regulatory assets	369,764	353,784	362,799
Investments	158,440	148,656	144,417
Operating lease right-of-use assets	120,534	115,323	118,764
Other	147,205	153,849	144,130
Total noncurrent assets	6,622,942	6,385,358	6,268,796
Total assets	8,125,499	7,683,059	7,730,611
Current liabilities:
Short-term borrowings	75,000	0	139,988
Long-term debt due within one year	1,558	16,540	65,810
Accounts payable	436,718	403,391	378,370
Taxes payable	96,708	48,970	53,505
Dividends payable	41,608	41,580	40,460
Accrued compensation	110,730	99,269	93,642
Regulatory liabilities due within one year	39,837	42,935	36,945
Operating lease liabilities due within one year	33,770	31,664	32,584
Asset retirement obligations due within one year	4,198	4,277	5,612
Other accrued liabilities	226,863	177,801	186,761
Total current liabilities	1,066,990	866,427	1,033,677
Noncurrent liabilities:
Long-term debt	2,268,732	2,226,567	2,180,946
Deferred income taxes	533,524	506,583	487,194
Regulatory liabilities	434,936	447,370	453,760
Asset retirement obligations	425,567	413,298	384,193
Operating lease liabilities	87,140	83,742	86,166
Other	295,845	291,826	309,069
Total noncurrent liabilities	4,045,744	3,969,386	3,901,328
Commitments and contingencies
Stockholders' equity:
Common stock	201,061	200,923	200,876
Other paid-in capital	1,366,494	1,355,404	1,351,990
Retained earnings	1,489,085	1,336,647	1,283,044
Accumulated other comprehensive loss	(40,249)	(42,102)	(36,678)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)	(3,626)
Total stockholders' equity	3,012,765	2,847,246	2,795,606
Total liabilities and stockholders' equity	$ 8,125,499	$ 7,683,059	$ 7,730,611
Common Stock, Shares Authorized	500,000,000	500,000,000	500,000,000
Common Stock, Par or Stated Value Per Share	$ 1	$ 1	$ 1
Common Stock, Shares, Issued	201,061,198	200,922,790	200,876,334
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, 2018		196,564,907
Treasury stock (in shares) at Dec. 31, 2018						(538,921)
Balance at Dec. 31, 2018	$ 2,566,775	$ 196,565	$ 1,248,576	$ 1,163,602	$ (38,342)	$ (3,626)
Net income	40,926			40,926
Other comprehensive income	774				774
Dividends declared on common stock	(40,019)			(40,019)
Stock-based compensation	1,617		1,617
Issuance of common stock upon vesting of stock-based compensation, tax withholding shares		246,214
Issuance of common stock upon vesting of stock-based compensation, tax withholding shares value		$ 246
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings			(3,261)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(3,015)
Issuance of common stock (shares)		1,505,687
Issuance of common stock	38,634	$ 1,506	37,128
Common stock balance (in shares) at Mar. 31, 2019		198,316,808
Treasury stock (in shares) at Mar. 31, 2019						(538,921)
Balance at Mar. 31, 2019	2,605,692	$ 198,317	1,284,060	1,164,509	(37,568)	$ (3,626)
Common stock balance (in shares) at Dec. 31, 2018		196,564,907
Treasury stock (in shares) at Dec. 31, 2018						(538,921)
Balance at Dec. 31, 2018	2,566,775	$ 196,565	1,248,576	1,163,602	(38,342)	$ (3,626)
Net income	240,388
Other comprehensive income	1,664
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	$ (3,015)
Common stock balance (in shares) at Sep. 30, 2019	200,876,334	200,876,334
Treasury stock (in shares) at Sep. 30, 2019						(538,921)
Balance at Sep. 30, 2019	$ 2,795,606	$ 200,876	1,351,990	1,283,044	(36,678)	$ (3,626)
Common stock balance (in shares) at Mar. 31, 2019		198,316,808
Treasury stock (in shares) at Mar. 31, 2019						(538,921)
Balance at Mar. 31, 2019	2,605,692	$ 198,317	1,284,060	1,164,509	(37,568)	$ (3,626)
Net income	61,825			61,825
Other comprehensive income	478				478
Dividends declared on common stock	(40,367)			(40,367)
Stock-based compensation	1,742		1,742
Issuance of common stock (shares)		1,222,302
Issuance of common stock	30,931	$ 1,222	29,709
Common stock balance (in shares) at Jun. 30, 2019		199,539,110
Treasury stock (in shares) at Jun. 30, 2019						(538,921)
Balance at Jun. 30, 2019	2,660,301	$ 199,539	1,315,511	1,185,967	(37,090)	$ (3,626)
Net income	137,637			137,637
Other comprehensive income	412				412
Dividends declared on common stock	(40,560)			(40,560)
Stock-based compensation	1,742		1,742
Issuance of common stock (shares)		1,337,224
Issuance of common stock	$ 36,074	$ 1,337	34,737
Common stock balance (in shares) at Sep. 30, 2019	200,876,334	200,876,334
Treasury stock (in shares) at Sep. 30, 2019						(538,921)
Balance at Sep. 30, 2019	$ 2,795,606	$ 200,876	1,351,990	1,283,044	(36,678)	$ (3,626)
Common stock balance (in shares) at Dec. 31, 2019	200,922,790	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	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	277,911
Other comprehensive income	1,853
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	$ (362)
Common stock balance (in shares) at Sep. 30, 2020	201,061,198	201,061,198
Treasury stock (in shares) at Sep. 30, 2020						(538,921)
Balance at Sep. 30, 2020	$ 3,012,765	$ 201,061	1,366,494	1,489,085	(40,249)	$ (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
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)
Net income	153,078			153,078
Other comprehensive income	560				560
Dividends declared on common stock	(41,872)			(41,872)
Stock-based compensation	$ 3,312		3,312
Common stock balance (in shares) at Sep. 30, 2020	201,061,198	201,061,198
Treasury stock (in shares) at Sep. 30, 2020						(538,921)
Balance at Sep. 30, 2020	$ 3,012,765	$ 201,061	$ 1,366,494	$ 1,489,085	$ (40,249)	$ (3,626)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities:
Net income	$ 277,911	$ 240,388
Income (loss) from discontinued operations, net of tax	(484)	26
Income from continuing operations	278,395	240,362
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	212,832	187,937
Deferred income taxes	16,409	49,222
Changes in current assets and liabilities, net of acquisitions:
Receivables	(100,141)	(238,373)
Inventories	(9,581)	2,480
Other current assets	1,269	(69,105)
Accounts payable	19,125	13,062
Other current liabilities	74,286	53,458
Other noncurrent changes	(10,139)	(35,361)
Net cash provided by continuing operations	482,455	203,682
Net cash used in discontinued operations	(688)	(579)
Net cash provided by operating activities	481,767	203,103
Investing activities:
Capital expenditures	(413,842)	(423,036)
Acquisitions, net of cash acquired	(71,479)	(53,263)
Net proceeds from sale or disposition of property and other	23,463	28,391
Investments	24	(717)
Net cash used in investing activities	(461,834)	(448,625)
Financing activities:
Issuance of short-term borrowings	75,000	169,977
Repayment of short-term borrowings	0	(30,000)
Issuance of long-term debt	100,125	302,724
Repayment of long-term debt	(73,699)	(166,956)
Proceeds from issuance of common stock	3,410	105,639
Dividends paid	(124,796)	(119,795)
Tax withholding on stock-based compensation	(362)	(3,015)
Net cash provided by (used in) financing activities	(20,322)	258,574
Increase (decrease) in cash and cash equivalents	(389)	13,052
Cash and cash equivalents -- beginning of year	66,459	53,948
Cash and cash equivalents -- end of period	$ 66,070	$ 67,000

Basis of presentation

Basis of presentation	9 Months Ended
	Sep. 30, 2020
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 2019 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. In March 2020, the World Health Organization declared the outbreak of COVID-19 a pandemic, and the President of the United States declared the COVID-19 outbreak as a national emergency. Governmental restrictions and guidelines implemented to control the spread of COVID-19 reduced commercial and interpersonal activity throughout the Company's areas of operation. Most of the Company's products and services are considered essential and accordingly operations have been generally allowed to continue. The Company has experienced some inefficiency impacts, including operation suspensions and interruptions at some locations to carry out preventive measures or in response to instances of positive tests or quarantines. The Company has assessed the impacts of the COVID-19 pandemic on its results of operations for the three and nine months ended September 30, 2020, and determined there were no material adverse impacts. In the first quarter of 2020, the Company recorded an out-of-period adjustment to correct the recognition of revenue on a construction contract, which was the result of an overstatement of operating revenue and receivables of $7.7 million and an understatement of operating expense and accounts payable of $1.2 million in the year ended December 31, 2019. This adjustment resulted in an after-tax reduction to net income of $6.7 million in the first quarter of 2020. The Company evaluated the impact of the out-of-period adjustment and concluded it was not material to any previously issued interim and annual consolidated financial statements and the adjustment was not material to the three months ended March 31, 2020 or the nine months ended September 30, 2020. Effective January 1, 2020, the Company adopted the requirements of the ASU on the measurement of credit losses on certain financial instruments following a modified retrospective approach, as further discussed in Notes 2 and 4. As such, results for reporting periods beginning on January 1, 2020, are presented under the new guidance, while prior period amounts are not adjusted and continue to be reported in accordance with historic accounting. The Company's adoption of this guidance did not have a material impact on its financial reporting. 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	9 Months Ended
	Sep. 30, 2020
Accounting Standards Update and Change in Accounting Principle [Abstract]
New accounting standards	New accounting standards Recently adopted accounting standards ASU 2016-13 - Measurement of Credit Losses on Financial Instruments In June 2016, the FASB issued guidance on the measurement of credit losses on certain financial instruments. The guidance introduced a new impairment model known as the current expected credit loss model that replaced the incurred loss impairment methodology previously included under GAAP. This guidance required entities to present certain investments in debt securities, trade accounts receivable and other financial assets at their net carrying value of the amount expected to be collected on the financial statements. The Company adopted the guidance on January 1, 2020, using a modified retrospective approach. The Company formed an implementation team to review and assess existing financial assets to identify and evaluate the financial assets subject to the new current expected credit loss model. The Company assessed the impact of the guidance on its processes and internal controls and identified and updated existing internal controls and processes to ensure compliance with the new guidance; such modifications were deemed insignificant. During the assessment phase, the Company identified the complete portfolio of assets subject to the current expected credit loss model. The Company determined the guidance did not have a material impact on its results of operations, financial position, cash flows or disclosures and did not record a material cumulative effect adjustment upon adoption. See Note 4 for additional information regarding the Company's expected credit losses. ASU 2018-13 - Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued guidance on modifying the disclosure requirements on fair value measurements as part of the disclosure framework project. The guidance modified, among other things, the disclosures required for Level 3 fair value measurements, including the range and weighted average of significant unobservable inputs. The guidance removed, among other things, the disclosure requirement to disclose transfers between Levels 1 and 2. The Company adopted the guidance on January 1, 2020, and determined the guidance did not have a material impact on its disclosures. Recently issued accounting standards not yet adopted ASU 2018-14 - Changes to the Disclosure Requirements for Defined Benefit Plans In August 2018, the FASB issued guidance on modifying the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans as part of the disclosure framework project. The guidance removes disclosures that are no longer considered cost beneficial, clarifies the specific requirements of disclosures and adds disclosure requirements identified as relevant. The guidance adds, among other things, the requirement to include an explanation for significant gains and losses related to changes in benefit obligations for the period. The guidance removes, among other things, the disclosure requirement to disclose the amount of net periodic benefit costs to be amortized over the next fiscal year from accumulated other comprehensive income (loss) and the effects a one percentage point change in assumed health care cost trend rates will have on certain benefit components. The guidance will be effective for the Company on January 1, 2021, and must be applied on a retrospective basis with early adoption permitted. The Company is evaluating the effects the adoption of the new guidance will have on its disclosures. ASU 2019-12 - Simplifying the Accounting for Income Taxes In December 2019, the FASB issued guidance on simplifying the accounting for income taxes by removing certain exceptions in ASC 740 and providing simplification amendments. The guidance removes exceptions on intraperiod tax allocations and reporting and provides simplification on accounting for franchise taxes, tax basis goodwill and tax law changes. The guidance will be effective for the Company on January 1, 2021, with early adoption permitted. Transition requirements vary among the exceptions and amendments which include retrospective, modified retrospective and prospective application. The Company has evaluated the effects of the new guidance and does not expect the guidance to have a material impact on its results of operations, financial position, cash flows or disclosures. ASU 2020-04 - Reference Rate Reform In March 2020, the FASB issued optional guidance to ease the facilitation of the effects of reference rate reform on financial reporting. The guidance applies to certain contract modifications, hedging relationships and other transactions that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. LIBOR is expected to be retired with a full phase-out by the end of 2021 and replaced by a new reference rate, which includes SOFR. The guidance can be applied beginning in the interim period that includes March 12, 2020, and cannot be applied to contract modifications or hedging relationships entered into or evaluated after December 31, 2022. The Company is currently updating its credit agreements to include language regarding the successor or alternate rate to LIBOR. 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	9 Months Ended
	Sep. 30, 2020
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	9 Months Ended
	Sep. 30, 2020
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 8. The Company's trade accounts receivable are all due in 12 months or less. The total balance of receivables past due 90 days or more was $48.9 million, $56.0 million and $46.7 million at September 30, 2020 and 2019, and December 31, 2019, 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 and general economic conditions of the various local economies, among others. Specific account balances are written off when management determines the amounts to be uncollectible. Details of the Company's expected credit losses were as follows: 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 Current expected credit loss provision 435 811 2 728 1,635 3,611 Less write-offs charged against the allowance 269 692 — 229 117 1,307 Credit loss recoveries collected 75 203 — — — 278 At September 30, 2020 $ 900 $ 1,853 $ 2 $ 6,124 $ 4,793 $ 13,672 The Company's allowance for doubtful accounts at September 30, 2019 and December 31, 2019, was $8.7 million and $8.5 million, respectively.

Inventories and natural gas in

Inventories and natural gas in storage	9 Months Ended
	Sep. 30, 2020
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: September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Aggregates held for resale $ 168,132 $ 143,157 $ 147,723 Asphalt oil 27,587 39,269 41,912 Materials and supplies 26,609 25,696 22,512 Merchandise for resale 21,525 23,902 22,232 Natural gas in storage (current) 27,135 32,164 22,058 Other 15,235 21,869 21,970 Total $ 286,223 $ 286,057 $ 278,407 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 $48.3 million, $48.2 million and $48.4 million at September 30, 2020 and 2019, and December 31, 2019, respectively.

Earnings per common share

Earnings per common share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Earnings per common 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 nonvested 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 Nine Months Ended September 30, September 30, 2020 2019 2020 2019 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 200,522 199,343 200,495 198,016 Effect of dilutive performance share awards and restricted stock units 97 40 20 17 Weighted average common shares outstanding - diluted 200,619 199,383 200,515 198,033 Shares excluded from the calculation of diluted earnings per share 87 155 139 243 Dividends declared per common share $ .2075 $ .2025 $ .6225 $ .6075

Accumulated other comprehensive

Accumulated other comprehensive income (loss)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Comprehensive income (loss)	Accumulated other comprehensive income (loss) The after-tax changes in the components of accumulated other comprehensive loss were as follows: Net Unrealized Postretirement Net Unrealized Total (In thousands) At December 31, 2019 $ (1,430) $ (40,734) $ 62 $ (42,102) Other comprehensive income before reclassifications — — 135 135 Amounts reclassified (to) from accumulated other comprehensive loss 111 462 (1) 572 Net current-period other comprehensive income 111 462 134 707 At March 31, 2020 $ (1,319) $ (40,272) $ 196 $ (41,395) 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) Other comprehensive loss before reclassifications — — (50) (50) Amounts reclassified from accumulated other comprehensive loss 111 471 28 610 Net current-period other comprehensive income (loss) 111 471 (22) 560 At September 30, 2020 $ (1,096) $ (39,321) $ 168 $ (40,249) Net Unrealized Postretirement Net Unrealized Total (In thousands) At December 31, 2018 $ (2,161) $ (36,069) $ (112) $ (38,342) Other comprehensive income before reclassifications — — 39 39 Amounts reclassified from accumulated other comprehensive loss 397 310 28 735 Net current-period other comprehensive income 397 310 67 774 At March 31, 2019 $ (1,764) $ (35,759) $ (45) $ (37,568) Other comprehensive income before reclassifications — — 79 79 Amounts reclassified from accumulated other comprehensive loss 111 276 12 399 Net current-period other comprehensive income 111 276 91 478 At June 30, 2019 $ (1,653) $ (35,483) $ 46 $ (37,090) Other comprehensive income before reclassifications — — 12 12 Amounts reclassified (to) from accumulated other comprehensive loss 112 292 (4) 400 Net current-period other comprehensive income 112 292 8 412 At September 30, 2019 $ (1,541) $ (35,191) $ 54 $ (36,678) The following amounts were reclassified between accumulated other comprehensive loss and 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 Nine Months Ended Location on Consolidated September 30, September 30, 2020 2019 2020 2019 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ (148) $ (148) $ (443) $ (443) Interest expense 37 36 109 (177) Income taxes (111) (112) (334) (620) Amortization of postretirement liability losses included in net periodic benefit cost (623) (387) (1,869) (1,162) Other income 152 95 456 284 Income taxes (471) (292) (1,413) (878) Reclassification adjustment on available-for-sale investments included in net income (35) 5 (43) (46) Other income 7 (1) 9 10 Income taxes (28) 4 (34) (36) Total reclassifications $ (610) $ (400) $ (1,781) $ (1,534)

Revenue from contracts with cus

Revenue from contracts with customers	9 Months Ended
	Sep. 30, 2020
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 16. Three Months Ended September 30, 2020 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 33,086 $ 48,399 $ — $ — $ — $ — $ 81,485 Commercial utility sales 35,688 28,731 — — — — 64,419 Industrial utility sales 8,428 4,454 — — — — 12,882 Other utility sales 1,779 — — — — — 1,779 Natural gas transportation — 11,159 27,583 — — — 38,742 Natural gas gathering — — 973 — — — 973 Natural gas storage — — 3,885 — — — 3,885 Contracting services — — — 448,569 — — 448,569 Construction materials — — — 608,673 — — 608,673 Intrasegment eliminations — — — (234,693) — — (234,693) Inside specialty contracting — — — — 352,845 — 352,845 Outside specialty contracting — — — — 187,202 — 187,202 Other 7,663 2,590 3,203 — 486 3,030 16,972 Intersegment eliminations (195) (185) (3,622) (110) (425) (3,006) (7,543) Revenues from contracts with customers 86,449 95,148 32,022 822,439 540,108 24 1,576,190 Revenues out of scope 998 (445) 46 — 10,500 — 11,099 Total external operating revenues $ 87,447 $ 94,703 $ 32,068 $ 822,439 $ 550,608 $ 24 $ 1,587,289 Three Months Ended September 30, 2019 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 30,376 $ 44,902 $ — $ — $ — $ — $ 75,278 Commercial utility sales 36,670 29,148 — — — — 65,818 Industrial utility sales 9,348 4,307 — — — — 13,655 Other utility sales 1,862 — — — — — 1,862 Natural gas transportation — 11,410 25,229 — — — 36,639 Natural gas gathering — — 2,510 — — — 2,510 Natural gas storage — — 3,044 — — — 3,044 Contracting services — — — 461,716 — — 461,716 Construction materials — — — 638,862 — — 638,862 Intrasegment eliminations — — — (231,078) — — (231,078) Inside specialty contracting — — — — 317,202 — 317,202 Outside specialty contracting — — — — 151,285 — 151,285 Other 9,380 2,708 5,534 — 45 2,884 20,551 Intersegment eliminations — — (3,831) (124) (1,226) (2,862) (8,043) Revenues from contracts with customers 87,636 92,475 32,486 869,376 467,306 22 1,549,301 Revenues out of scope 2,209 1,167 47 — 11,075 — 14,498 Total external operating revenues $ 89,845 $ 93,642 $ 32,533 $ 869,376 $ 478,381 $ 22 $ 1,563,799 Nine Months Ended September 30, 2020 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 93,389 $ 313,753 $ — $ — $ — $ — $ 407,142 Commercial utility sales 99,152 184,754 — — — — 283,906 Industrial utility sales 26,867 18,633 — — — — 45,500 Other utility sales 5,018 — — — — — 5,018 Natural gas transportation — 33,307 82,980 — — — 116,287 Natural gas gathering — — 4,244 — — — 4,244 Natural gas storage — — 10,035 — — — 10,035 Contracting services — — — 850,326 — — 850,326 Construction materials — — — 1,299,081 — — 1,299,081 Intrasegment eliminations — — — (443,516) — — (443,516) Inside specialty contracting — — — — 1,049,975 — 1,049,975 Outside specialty contracting — — — — 478,047 — 478,047 Other 23,830 7,800 9,807 — 1,249 8,882 51,568 Intersegment eliminations (586) (555) (36,820) (262) (3,674) (8,952) (50,849) Revenues from contracts with customers 247,670 557,692 70,246 1,705,629 1,525,597 (70) 4,106,764 Revenues out of scope 2,123 4,949 135 — 33,620 — 40,827 Total external operating revenues $ 249,793 $ 562,641 $ 70,381 $ 1,705,629 $ 1,559,217 $ (70) $ 4,147,591 Nine Months Ended September 30, 2019 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 93,368 $ 316,521 $ — $ — $ — $ — $ 409,889 Commercial utility sales 105,572 192,191 — — — — 297,763 Industrial utility sales 27,576 18,495 — — — — 46,071 Other utility sales 5,540 — — — — — 5,540 Natural gas transportation — 33,686 75,091 — — — 108,777 Natural gas gathering — — 7,027 — — — 7,027 Natural gas storage — — 8,313 — — — 8,313 Contracting services — — — 841,881 — — 841,881 Construction materials — — — 1,262,938 — — 1,262,938 Intrasegment eliminations — — — (412,144) — — (412,144) Inside specialty contracting — — — — 936,008 — 936,008 Outside specialty contracting — — — — 391,971 — 391,971 Other 26,918 9,544 14,523 — 70 13,631 64,686 Intersegment eliminations — — (35,298) (388) (2,076) (13,566) (51,328) Revenues from contracts with customers 258,974 570,437 69,656 1,692,287 1,325,973 65 3,917,392 Revenues out of scope 4,449 (781) 171 — 37,332 — 41,171 Total external operating revenues $ 263,423 $ 569,656 $ 69,827 $ 1,692,287 $ 1,363,305 $ 65 $ 3,958,563 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: September 30, 2020 December 31, 2019 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 135,958 $ 109,078 $ 26,880 Receivables, net Contract liabilities - current (158,923) (142,768) (16,155) Accounts payable Contract liabilities - noncurrent (62) (19) (43) Noncurrent liabilities - other Net contract liabilities $ (23,027) $ (33,709) $ 10,682 The Company recognized $15.6 million and $137.3 million in revenue for the three and nine months ended September 30, 2020, respectively, which was previously included in contract liabilities at December 31, 2019. The Company recognized $7.5 million and $86.5 million in revenue for the three and nine months ended September 30, 2019, respectively, which was previously included in contract liabilities at December 31, 2018. The Company recognized a net increase in revenues of $34.7 million and $58.8 million for the three and nine months ended September 30, 2020, respectively, from performance obligations satisfied in prior periods. The Company recognized a net increase in revenues of $21.8 million and $40.3 million for the three and nine months ended September 30, 2019, 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 two years, respectively.

Business Combinations

Business Combinations	9 Months Ended
	Sep. 30, 2020
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 were material to the Company's financial position or results of operations. For all business combinations, the Company preliminarily allocates the purchase price of the acquisitions to the assets acquired and liabilities assumed based on their estimated fair values as of the acquisition dates and are considered provisional until final fair values are determined or the measurement period has passed. The Company expects to record adjustments as it accumulates the information needed to estimate the fair value of assets acquired and liabilities assumed, including working capital balances; identifiable intangible assets; property, plant and equipment; total consideration and goodwill. The excess of the purchase price over the aggregate fair values is recorded as goodwill. The Company calculated the fair value of the assets acquired in 2020 and 2019 using a market or cost approach (or a combination of both). Fair values for some of the assets were determined based on Level 3 inputs including estimated future cash flows, discount rates, growth rates, sales projections, retention rates and terminal values, all of which require significant management judgment and are susceptible to change. The final fair value of the net assets acquired may result in adjustments to the assets and liabilities, including goodwill, and will be made as soon as practical, but no later than 12 months from the respective acquisition dates. Any subsequent measurement period adjustments are not expected to have a material impact on the Company's 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. The following are the acquisitions made during 2020 and 2019 at the construction materials and contracting segment: • In February 2020, the Company acquired the assets of Oldcastle Infrastructure Spokane, a prestressed-concrete business in Washington. • In December 2019, the Company acquired the assets of Roadrunner Ready Mix, Inc., a provider of ready-mixed concrete in Idaho. • In March 2019, the Company acquired Viesko Redi-Mix, Inc., a provider of ready-mixed concrete in Oregon. The following are the acquisitions made during 2020 and 2019 at the construction services segment: • In February 2020, the Company acquired PerLectric, Inc., an electrical construction company in Virginia. • In September 2019, the Company purchased the assets of Pride Electric, Inc., an electrical construction company in Washington. The total purchase price for acquisitions that occurred in 2020 was $78.2 million, subject to certain adjustments, with cash acquired totaling $1.7 million. The purchase price includes consideration paid of $71.5 million and $5.0 million of indemnity holdback liabilities. The amounts allocated to the aggregated assets acquired and liabilities assumed during 2020 were as follows: $45.9 million to current assets; $4.9 million to property, plant and equipment; $31.3 million to goodwill; $17.6 million to other intangible assets; $21.2 million to current liabilities and $300,000 to noncurrent liabilities. During 2020, measurement period adjustments were made to previously reported provisional amounts, which increased goodwill by $400,000. At September 30, 2020, the purchase price allocations for these acquisitions were preliminary and will be finalized within 12 months of the respective acquisition dates. The Company issued debt to finance these acquisitions. In 2019, the gross aggregate consideration for acquisitions was $56.8 million, subject to certain adjustments, and included $1.2 million of debt assumed. The amounts allocated to the aggregated assets acquired and liabilities assumed during 2019 were as follows: $15.8 million to current assets; $16.7 million to property, plant and equipment; $23.1 million to goodwill; $6.7 million to other intangible assets; $500,000 to other noncurrent assets; $5.9 million to current liabilities and $100,000 to noncurrent liabilities. At December 31, 2019, the purchase price adjustments for Viesko Redi-Mix, Inc. had been settled and no material adjustments were made to the provisional accounting. At September 30, 2020, the measurement period for Pride Electric, Inc. ended with no material adjustments made to the provisional accounting. At September 30, 2020, the purchase price allocation for Roadrunner Ready Mix, Inc. was preliminary and will be finalized within 12 months of the acquisition date. The Company issued debt and equity securities to finance these acquisitions. Costs incurred for acquisitions are included in operation and maintenance expense on the Consolidated Statements of Income and were not material for the nine months ended September 30, 2020 and 2019.

Leases

Leases	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Leases of Lessor Disclosure	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 $10.7 million and $34.0 million for the three and nine months ended September 30, 2020, respectively. The Company recognized revenue from operating leases of $11.2 million and $37.7 million for the three and nine months ended September 30, 2019, respectively. At September 30, 2020, the Company had $8.4 million of lease receivables with a majority due within 12 months.

Goodwill and other intangible a

Goodwill and other intangible assets	9 Months Ended
	Sep. 30, 2020
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, 2020 Goodwill Measurement Balance at September 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 24,436 400 143,224 Total $ 681,358 $ 30,919 $ 400 $ 712,677 Balance at January 1, 2019 Goodwill Measurement Balance at September 30, 2019 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 209,421 14,473 (6,669) 217,225 Construction services 109,765 8,623 — 118,388 Total $ 664,922 $ 23,096 $ (6,669) $ 681,349 Balance at January 1, 2019 Goodwill Measurement Balance at December 31, 2019 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 209,421 14,482 (6,669) 217,234 Construction services 109,765 8,623 — 118,388 Total $ 664,922 $ 23,105 $ (6,669) $ 681,358 Other amortizable intangible assets were as follows: September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Customer relationships $ 27,551 $ 18,011 $ 17,958 Less accumulated amortization 5,958 5,823 6,268 21,593 12,188 11,690 Noncompete agreements 3,941 3,419 3,439 Less accumulated amortization 2,176 1,868 1,957 1,765 1,551 1,482 Other 12,853 7,488 8,094 Less accumulated amortization 9,835 5,716 6,020 3,018 1,772 2,074 Total $ 26,376 $ 15,511 $ 15,246 The previous tables include goodwill and intangible assets associated with the business combinations completed during 2020 and 2019. For more information related to these business combinations, see Note 9. Amortization expense for amortizable intangible assets for the three and nine months ended September 30, 2020, was $2.1 million and $6.8 million, respectively. Amortization expense for amortizable intangible assets for the three and nine months ended September 30, 2019, was $500,000 and $1.6 million, respectively. Estimated amortization expense for identifiable intangible assets as of September 30, 2020, was: Remainder of 2021 2022 2023 2024 Thereafter (In thousands) Amortization expense $ 2,462 $ 4,579 $ 4,108 $ 3,975 $ 3,653 $ 7,599

Regulatory assets and liabiliti

Regulatory assets and liabilities	9 Months Ended
	Sep. 30, 2020
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 * September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 48,478 $ 39,383 $ 42,823 Cost recovery mechanisms Up to 1 year 8,177 8,706 6,288 Conservation programs Up to 1 year 7,857 7,776 6,963 Other Up to 1 year 14,613 13,316 7,539 79,125 69,181 63,613 Noncurrent: Pension and postretirement benefits ** 157,015 165,843 157,069 Asset retirement obligations Over plant lives 68,815 64,771 66,000 Plant to be retired - 57,499 26,152 32,931 Manufactured gas plant site remediation - 25,964 15,510 15,126 Natural gas costs recoverable through rate adjustments Up to 3 years 24,677 53,618 46,381 Cost recovery mechanisms Up to 10 years 14,281 12,206 13,108 Taxes recoverable from customers Over plant lives 10,847 11,600 11,486 Long-term debt refinancing costs Up to 17 years 3,826 4,439 4,286 Other Up to 19 years 6,840 8,660 7,397 369,764 362,799 353,784 Total regulatory assets $ 448,889 $ 431,980 $ 417,397 Regulatory liabilities: Current: Natural gas costs refundable through rate adjustments $ 20,556 $ 19,194 $ 23,825 Electric fuel and purchased power deferral 6,171 2,040 5,824 Taxes refundable to customers 4,223 4,309 3,472 Other 8,887 11,402 9,814 39,837 36,945 42,935 Noncurrent: Taxes refundable to customers 232,186 253,703 246,034 Plant removal and decommissioning costs 173,367 174,595 173,722 Pension and postretirement benefits 17,991 15,190 18,065 Other 11,392 10,272 9,549 434,936 453,760 447,370 Total regulatory liabilities $ 474,773 $ 490,705 $ 490,305 Net regulatory position $ (25,884) $ (58,725) $ (72,908) * Estimated recovery period for regulatory assets currently being recovered in rates charged to customers. ** Recovered as expense is incurred or cash contributions are made. At September 30, 2020 and 2019, and December 31, 2019, approximately $318.2 million, $278.6 million and $276.5 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. 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 that it intends to retire one aging coal-fired electric generating unit in early 2021 and two units in early 2022. The Company has accelerated the depreciation related to these facilities in property, plant and equipment and has recorded the difference between the accelerated depreciation, in accordance with GAAP, and the depreciation approved for rate-making purposes as regulatory assets. The Company expects to recover the regulatory assets related to the plants to be retired in future rates. If, for any reason, the Company's regulated businesses cease to meet the criteria for application of regulatory accounting for all or part of their operations, the regulatory assets and liabilities relating to those portions ceasing to meet such criteria would be removed from the balance sheet and included in the statement of income or accumulated other comprehensive income (loss) in the period in which the discontinuance of regulatory accounting occurs.

Fair value measurements

Fair value measurements	9 Months Ended
	Sep. 30, 2020
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 an insurance contract, to satisfy its obligations under its unfunded, nonqualified defined benefit 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 $95.7 million, $84.2 million and $87.0 million, at September 30, 2020 and 2019, and December 31, 2019, respectively, are classified as investments on the Consolidated Balance Sheets. The net unrealized gains on these investments were $3.3 million and $8.7 million for the three and nine months ended September 30, 2020, respectively. The net unrealized gains on these investments were $1.1 million and $10.4 million for the three and nine months ended September 30, 2019, 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: September 30, 2020 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,813 $ 213 $ 4 $ 10,022 U.S. Treasury securities 1,166 3 — 1,169 Total $ 10,979 $ 216 $ 4 $ 11,191 September 30, 2019 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,577 $ 86 $ 16 $ 9,647 U.S. Treasury securities 1,258 — 1 1,257 Total $ 10,835 $ 86 $ 17 $ 10,904 December 31, 2019 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,804 $ 87 $ 10 $ 9,881 U.S. Treasury securities 1,228 1 — 1,229 Total $ 11,032 $ 88 $ 10 $ 11,110 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 Level 2 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 Level 2 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 Level 2 insurance contract is 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 September 30, 2020, Using Quoted Prices in Significant Significant Balance at September 30, 2020 (In thousands) Assets: Money market funds $ — $ 8,478 $ — $ 8,478 Insurance contract* — 95,687 — 95,687 Available-for-sale securities: Mortgage-backed securities — 10,022 — 10,022 U.S. Treasury securities — 1,169 — 1,169 Total assets measured at fair value $ — $ 115,356 $ — $ 115,356 * The insurance contract invests approximately 68 percent in fixed-income investments, 15 percent in common stock of large-cap companies, 6 percent in common stock of mid-cap companies, 6 percent in common stock of small-cap companies, 4 percent in target date investments and 1 percent in cash equivalents. Fair Value Measurements at September 30, 2019, Using Quoted Prices in Significant Significant Balance at September 30, 2019 (In thousands) Assets: Money market funds $ — $ 7,472 $ — $ 7,472 Insurance contract* — 84,222 — 84,222 Available-for-sale securities: Mortgage-backed securities — 9,647 — 9,647 U.S. Treasury securities — 1,257 — 1,257 Total assets measured at fair value $ — $ 102,598 $ — $ 102,598 * The insurance contract invests approximately 53 percent in fixed-income investments, 21 percent in common stock of large-cap companies, 11 percent in common stock of mid-cap companies, 10 percent in common stock of small-cap companies, 3 percent in target date investments and 2 percent in cash equivalents. Fair Value Measurements at December 31, 2019, Using Quoted Prices in Significant Significant Balance at December 31, 2019 (In thousands) Assets: Money market funds $ — $ 8,440 $ — $ 8,440 Insurance contract* — 87,009 — 87,009 Available-for-sale securities: Mortgage-backed securities — 9,881 — 9,881 U.S. Treasury securities — 1,229 — 1,229 Total assets measured at fair value $ — $ 106,559 $ — $ 106,559 * The insurance contract invests approximately 51 percent in fixed-income investments, 23 percent in common stock of large-cap companies, 12 percent in common stock of mid-cap companies, 10 percent in common stock of small-cap companies, 3 percent in target date investments and 1 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. In the second quarter of 2019, the Company reviewed a non-utility investment at its electric and natural gas distribution segments for impairment. This was a cost-method investment and was written down to zero using the income approach to determine its fair value, requiring the Company to record a write-down of $2.0 million, before tax. The fair value of this investment was categorized as Level 3 in the fair value hierarchy. This reduction is reflected in investments on the Company's Consolidated Balance Sheet, as well as within other income on the Consolidated Statements of Income. The Company performed a fair value assessment of the assets acquired and liabilities assumed in the business combinations that have occurred during 2020 and 2019. For more information on these Level 2 and Level 3 fair value measurements, see Note 9. 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: September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Carrying amount $ 2,270,290 $ 2,246,756 $ 2,243,107 Fair value $ 2,593,743 $ 2,450,209 $ 2,418,631 The carrying amounts of the Company's remaining financial instruments included in current assets and current liabilities approximate their fair values .

Debt

Debt	9 Months Ended
	Sep. 30, 2020
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 September 30, 2020. In the event the Company's 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. Due to the early impacts of the COVID-19 pandemic on the short-term capital markets, the Company temporarily borrowed under its revolving credit agreements in addition to accessing the commercial paper markets in the first half of 2020 . At September 30, 2020, all borrowings under the revolving credit agreements for Montana-Dakota and Centennial had been repaid. Long-term debt Long-term Debt Outstanding Long-term debt outstanding was as follows: Weighted September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Senior Notes due on dates ranging from October 22, 2022 to June 15, 2060 4.43 % $ 1,900,000 $ 1,655,000 $ 1,850,000 Commercial paper supported by revolving credit agreements 0.44 % 214,150 281,800 222,900 Term Loan Agreement due on September 3, 2032 2.00 % 8,400 209,100 9,100 Credit agreements due on June 7, 2024 2.40 % 91,000 31,000 89,050 Medium-Term Notes due on dates ranging from September 15, 2027 to March 16, 2029 7.32 % 35,000 50,000 50,000 Other notes due on dates ranging from July 15, 2021 to November 30, 2038 4.60 % 28,284 26,083 29,117 Less unamortized debt issuance costs 6,526 6,074 7,010 Less discount 18 153 50 Total long-term debt 2,270,290 2,246,756 2,243,107 Less current maturities 1,558 65,810 16,540 Net long-term debt $ 2,268,732 $ 2,180,946 $ 2,226,567 Schedule of Debt Maturities Long-term debt maturities, which excludes unamortized debt issuance costs and discount, at September 30, 2020, were as follows: Remainder of 2021 2022 2023 2024 Thereafter (In thousands) Long-term debt maturities $ 28 $ 1,528 $ 148,038 $ 77,921 $ 366,571 $ 1,682,748

Cash flow information

Cash flow information	9 Months Ended
	Sep. 30, 2020
Supplemental Cash Flow Information [Abstract]
Cash flow information	Cash flow information Cash expenditures for interest and income taxes were as follows: Nine Months Ended September 30, 2020 2019 (In thousands) Interest, net* $ 63,086 $ 64,596 Income taxes paid, net** $ 43,448 $ 1,816 * AFUDC - borrowed was $2.0 million for the nine months ended September 30, 2020 and 2019. ** Income taxes paid, including discontinued operations, were $43.5 million and $2.0 million for the nine months ended September 30, 2020 and 2019, respectively. Noncash investing and financing transactions were as follows: September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 41,315 $ 46,770 $ 54,880 Property, plant and equipment additions in accounts payable $ 33,240 $ 34,368 $ 46,119 Accrual for holdback payment related to a business combination $ 5,000 $ — $ — Debt assumed in connection with a business combination $ — $ 1,163 $ 1,163

Business segment data

Business segment data	9 Months Ended
	Sep. 30, 2020
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 vast majority of 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, underground storage and gathering services through regulated and non-regulated pipeline systems primarily in the Rocky Mountain and northern Great Plains regions of the United States. This segment also provides cathodic protection and other energy-related services. 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, including Alaska and Hawaii. The construction services segment provides inside and outside specialty contracting services. 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 government 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 1 of the Notes to Consolidated Financial Statements in the 2019 Annual Report. Information on the Company's segments was as follows: Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 (In thousands) External operating revenues: Regulated operations: Electric $ 87,447 $ 89,845 $ 249,793 $ 263,423 Natural gas distribution 94,703 93,642 562,641 569,656 Pipeline 27,965 25,957 57,717 52,230 210,115 209,444 870,151 885,309 Non-regulated operations: Pipeline 4,103 6,576 12,664 17,597 Construction materials and contracting 822,439 869,376 1,705,629 1,692,287 Construction services 550,608 478,381 1,559,217 1,363,305 Other 24 22 (70) 65 1,377,174 1,354,355 3,277,440 3,073,254 Total external operating revenues $ 1,587,289 $ 1,563,799 $ 4,147,591 $ 3,958,563 Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 (In thousands) Intersegment operating revenues: Regulated operations: Electric $ 195 $ — $ 586 $ — Natural gas distribution 185 — 555 — Pipeline 3,543 3,750 36,583 35,098 3,923 3,750 37,724 35,098 Non-regulated operations: Pipeline 79 81 237 200 Construction materials and contracting 110 124 262 388 Construction services 425 1,226 3,674 2,076 Other 3,006 2,862 8,952 13,566 3,620 4,293 13,125 16,230 Intersegment eliminations (7,543) (8,043) (50,849) (51,328) Total intersegment operating revenues $ — $ — $ — $ — Operating income (loss): Electric $ 21,159 $ 21,930 $ 48,827 $ 49,708 Natural gas distribution (18,393) (15,565) 32,285 32,132 Pipeline 11,762 11,416 35,406 32,017 Construction materials and contracting 148,522 143,024 179,994 147,622 Construction services 40,507 29,950 102,185 89,381 Other 154 (1,285) 339 140 Total operating income $ 203,711 $ 189,470 $ 399,036 $ 351,000 Net income (loss): Regulated operations: Electric $ 16,787 $ 16,291 $ 40,314 $ 39,267 Natural gas distribution (17,614) (15,625) 13,795 14,623 Pipeline 7,812 6,933 23,882 20,316 6,985 7,599 77,991 74,206 Non-regulated operations: Pipeline 189 801 444 1,380 Construction materials and contracting 107,307 102,611 122,113 97,328 Construction services 29,789 21,113 74,544 63,982 Other 8,745 4,004 3,303 3,466 146,030 128,529 200,404 166,156 Income from continuing operations 153,015 136,128 278,395 240,362 Income (loss) from discontinued operations, net of tax 63 1,509 (484) 26 Net income $ 153,078 $ 137,637 $ 277,911 $ 240,388

Employee benefit plans

Employee benefit plans	9 Months Ended
	Sep. 30, 2020
Retirement Benefits [Abstract]
Pension and other postretirement plans	Employee benefit plans Pension and other postretirement plans The Company has noncontributory qualified defined benefit pension plans and other postretirement benefit plans for certain eligible employees. Components of net periodic benefit cost (credit) for the Company's pension and other postretirement benefit plans were as follows: Pension Benefits Other Three Months Ended September 30, 2020 2019 2020 2019 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 383 $ 286 Interest cost 3,023 3,806 609 746 Expected return on assets (4,987) (4,559) (1,115) (1,201) Amortization of prior service credit — — (349) (289) Amortization of net actuarial loss 1,793 1,387 71 27 Net periodic benefit cost (credit), including amount capitalized (171) 634 (401) (431) Less amount capitalized — — 39 26 Net periodic benefit cost (credit) $ (171) $ 634 $ (440) $ (457) Pension Benefits Other Nine Months Ended September 30, 2020 2019 2020 2019 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 1,149 $ 857 Interest cost 9,070 11,419 1,827 2,239 Expected return on assets (14,962) (13,677) (3,764) (3,603) Amortization of prior service credit — — (1,048) (866) Amortization of net actuarial loss 5,379 4,160 215 82 Net periodic benefit cost (credit), including amount capitalized (513) 1,902 (1,621) (1,291) Less amount capitalized — — 106 84 Net periodic benefit cost (credit) $ (513) $ 1,902 $ (1,727) $ (1,375) The components of net periodic benefit cost (credit), other than the service cost component, are included in other income on the Consolidated Statements of Income. The service cost component is included in operation and maintenance expense on the Consolidated Statements of Income. Nonqualified defined benefit plans In addition to the qualified defined benefit pension plans reflected in the table at the beginning of this note, the Company also has unfunded, nonqualified defined benefit plans for executive officers and certain key management employees. The Company's net periodic benefit cost for these plans for the three and nine months ended September 30, 2020, was $1.0 million and $2.9 million, respectively. The Company's net periodic benefit cost for these plans for the three and nine months ended September 30, 2019, was $1.1 million and $3.3 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	9 Months Ended
	Sep. 30, 2020
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 regulatory proceedings and cases by jurisdiction, including the status of each open request, as well as updates to those reported in the 2019 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. MNPUC On September 27, 2019, Great Plains filed an application with the MNPUC for a natural gas rate increase of approximately $2.9 million annually or approximately 12.0 percent above current rates. The requested increase was primarily to recover investments in facilities to enhance safety and reliability and the depreciation and taxes associated with the increase in investment. On November 22, 2019, Great Plains received approval to implement an interim rate increase of approximately $2.6 million or approximately 11.0 percent, subject to refund, effective January 1, 2020. On October 26, 2020, the MNPUC issued a final order authorizing an annual increase in revenues of approximately $2.6 million or approximately 11.5 percent. Great Plains shall submit compliance filings within 30 days of the order. MTPSC On May 8, 2020, Montana-Dakota filed a request with the MTPSC to use deferred accounting for costs related to the COVID-19 pandemic. This matter is pending before the MTPSC. On June 22, 2020, Montana-Dakota filed an application with the MTPSC for a natural gas rate increase of approximately $8.6 million annually or approximately 13.4 percent above current rates. The requested increase was primarily to recover investments in facilities that were made to enhance system safety and reliability, as well as the depreciation, taxes and operation and maintenance costs associated with this increase in investment. The Company requested an interim rate increase of approximately $4.9 million or approximately 8.2 percent, subject to refund, to be effective February 1, 2021. This matter is pending before the MTPSC. NDPSC On April 24, 2020, Montana-Dakota filed a request with the NDPSC to use deferred accounting for costs related to the COVID-19 pandemic. This matter is pending before the NDPSC. On July 17, 2020, Montana-Dakota filed an annual update to its transmission cost adjustment rider with the NDPSC requesting to recover revenues of approximately $15.5 million, which includes a true-up of the prior period adjustment, resulting in an increase of approximately $6.3 million over current rates. This filing includes approximately $3.3 million related to transmission capital projects. On October 28, 2020, the NDPSC approved the increase with rates effective November 1, 2020. Due to COVID-19, the NDPSC extended the recovery period of the under-recovered balance of approximately $1.6 million to two years, which was included in the total increase. On August 26, 2020, Montana-Dakota filed an application with the NDPSC for a natural gas rate increase of approximately $9.0 million annually or approximately 7.8 percent above current rates. The requested increase was primarily to recover investments in facilities to enhance system safety and reliability and the depreciation and taxes associated with the increase in investment. Montana-Dakota also requested an interim increase of approximately $6.9 million or approximately 6.0 percent, subject to refund, to be effective January 1, 2021. This matter is pending before the NDPSC. OPUC On March 26, 2020, Cascade filed a request with the OPUC to use deferred accounting for costs related to the COVID-19 pandemic. On October 20, 2020, the OPUC approved this request. On March 31, 2020, Cascade filed a natural gas general rate case with the OPUC requesting an increase in annual revenue of approximately $4.9 million or approximately 7.2 percent, which included a request for an additional recovery of environmental remediation deferred costs of approximately $364,000. On September 30, 2020, Cascade filed a settlement agreement with the OPUC reflecting an annual increase in revenues of approximately $3.2 million or approximately 4.8 percent. This filing includes a proposed effective date of February 1, 2021. This matter is pending before the OPUC. SDPUC On May 1, 2020, Montana-Dakota filed a request with the SDPUC to use deferred accounting for costs related to the COVID-19 pandemic. On August 19, 2020, the SDPUC approved this request with an accounting order to track expenses and revenues related to the COVID-19 pandemic beginning on March 13, 2020. WUTC On May 27, 2020, Cascade filed a request with the WUTC to use deferred accounting for costs related to the COVID-19 pandemic. This matter is pending before the WUTC. On May 29, 2020, Cascade filed its annual pipeline cost recovery mechanism requesting an increase in annual revenue of approximately $1.0 million or approximately 0.4 percent. On October 14, 2020, Cascade filed an update requesting an increase in annual revenue of approximately $1.1 million or approximately 0.5 percent, which reflects actual costs as of September 30, 2020. On October 29, 2020, the filing was approved with rates effective November 1, 2020. 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 WUTC has 11 months to render a final decision on the rate case. The requested increase was primarily to recover investments made in infrastructure upgrades, as well as increased operation and maintenance costs. This matter is pending before the WUTC. FERC On September 1, 2020, Montana-Dakota filed an update to its transmission formula rate under the MISO tariff for its multi-value project for $12.9 million, which is effective January 1, 2021.

Contingencies

Contingencies	9 Months Ended
	Sep. 30, 2020
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 September 30, 2020 and 2019, and December 31, 2019, the Company accrued liabilities which have not been discounted, including liabilities held for sale, of $72.7 million, $30.6 million and $29.1 million, respectively. At September 30, 2020 and 2019, and December 31, 2019, the Company also recorded corresponding insurance receivables of $49.1 million, $15.3 million and $16.2 million, respectively, and regulatory assets of $20.9 million, $12.0 million and $10.5 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 2019 Annual Report other than as set forth below. Manufactured Gas Plant Sites A claim was made against Cascade for contamination at the Bremerton Gasworks Superfund Site in Bremerton, Washington, which was received in 1997. A preliminary investigation has found soil and groundwater at the site contain contaminants requiring further investigation and cleanup. The EPA conducted a Targeted Brownfields Assessment of the site and released a report summarizing the results of that assessment in August 2009. The assessment confirmed that contaminants have affected soil and groundwater at the site, as well as sediments in the adjacent Port Washington Narrows. In April 2010, the Washington DOE issued notice it considered Cascade a PRP for hazardous substances at the site. In May 2012, the EPA added the site to the National Priorities List of Superfund sites. Cascade entered into an administrative settlement agreement and consent order with the EPA regarding the scope and schedule for a remedial investigation and feasibility study for the site. Current estimates for the cost to complete the remedial investigation and feasibility study are approximately $7.6 million of which $5.4 million has been incurred. Based on the site investigation, preliminary remediation alternative costs were provided by consultants in August 2020; therefore, the accrual for these costs was increased in the third quarter of 2020 by $11.1 million. The preliminary information received through the completion of the data report allowed for the projection of possible costs for a variety of site configurations, remedial measures and potential natural resource damage claims of between $13.6 million and $71.0 million. Cascade has accrued $2.2 million for the remedial investigation and feasibility study, as well as $17.5 million for remediation of this site. The accrual for remediation cost will be reviewed and adjusted, if necessary, after the completion of the feasibility study. In April 2010, Cascade filed a petition with the WUTC for authority to defer the costs incurred in relation to the environmental remediation of this site. The WUTC approved the petition in September 2010, subject to conditions set forth in the order. The Company has received notices from and entered into agreements with certain of its insurance carriers that they will participate in defense for certain contamination claims subject to full and complete reservations of rights and defenses to insurance coverage. To the extent these claims are not covered by insurance, the Company intends to seek recovery of remediation costs through its natural gas rates charged to customers. 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 September 30, 2020, the fixed maximum amounts guaranteed under these agreements aggregated $255.5 million. Certain of the guarantees also have no fixed maximum amounts specified. At September 30, 2020, the amounts of scheduled expiration of the maximum amounts guaranteed under these agreements aggregate to $23.8 million in 2020; $199.7 million in 2021; $16.1 million in 2022; $5.3 million in 2023; $500,000 in 2024; $1.1 million thereafter; and $9.0 million, which has no scheduled maturity date. There were no amounts outstanding under the previously mentioned guarantees at September 30, 2020. 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 September 30, 2020, the fixed maximum amounts guaranteed under these letters of credit aggregated $22.5 million. At September 30, 2020, the amounts of scheduled expiration of the maximum amounts guaranteed under these letters of credit aggregate to $20.2 million in 2020; $1.8 million in 2021 and $500,000 in 2022. There were no amounts outstanding under the previously mentioned letters of credit at September 30, 2020. 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 September 30, 2020. 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 September 30, 2020, approximately $922.7 million 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 September 30, 2020, 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 $34.2 million.

Basis of presentation (Policies

Basis of presentation (Policies)	9 Months Ended
	Sep. 30, 2020
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 2019 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)	9 Months Ended
	Sep. 30, 2020
Accounting Standards Update and Change in Accounting Principle [Abstract]
New accounting standards	Recently adopted accounting standards ASU 2016-13 - Measurement of Credit Losses on Financial Instruments In June 2016, the FASB issued guidance on the measurement of credit losses on certain financial instruments. The guidance introduced a new impairment model known as the current expected credit loss model that replaced the incurred loss impairment methodology previously included under GAAP. This guidance required entities to present certain investments in debt securities, trade accounts receivable and other financial assets at their net carrying value of the amount expected to be collected on the financial statements. The Company adopted the guidance on January 1, 2020, using a modified retrospective approach. The Company formed an implementation team to review and assess existing financial assets to identify and evaluate the financial assets subject to the new current expected credit loss model. The Company assessed the impact of the guidance on its processes and internal controls and identified and updated existing internal controls and processes to ensure compliance with the new guidance; such modifications were deemed insignificant. During the assessment phase, the Company identified the complete portfolio of assets subject to the current expected credit loss model. The Company determined the guidance did not have a material impact on its results of operations, financial position, cash flows or disclosures and did not record a material cumulative effect adjustment upon adoption. See Note 4 for additional information regarding the Company's expected credit losses. ASU 2018-13 - Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued guidance on modifying the disclosure requirements on fair value measurements as part of the disclosure framework project. The guidance modified, among other things, the disclosures required for Level 3 fair value measurements, including the range and weighted average of significant unobservable inputs. The guidance removed, among other things, the disclosure requirement to disclose transfers between Levels 1 and 2. The Company adopted the guidance on January 1, 2020, and determined the guidance did not have a material impact on its disclosures. Recently issued accounting standards not yet adopted ASU 2018-14 - Changes to the Disclosure Requirements for Defined Benefit Plans In August 2018, the FASB issued guidance on modifying the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans as part of the disclosure framework project. The guidance removes disclosures that are no longer considered cost beneficial, clarifies the specific requirements of disclosures and adds disclosure requirements identified as relevant. The guidance adds, among other things, the requirement to include an explanation for significant gains and losses related to changes in benefit obligations for the period. The guidance removes, among other things, the disclosure requirement to disclose the amount of net periodic benefit costs to be amortized over the next fiscal year from accumulated other comprehensive income (loss) and the effects a one percentage point change in assumed health care cost trend rates will have on certain benefit components. The guidance will be effective for the Company on January 1, 2021, and must be applied on a retrospective basis with early adoption permitted. The Company is evaluating the effects the adoption of the new guidance will have on its disclosures. ASU 2019-12 - Simplifying the Accounting for Income Taxes In December 2019, the FASB issued guidance on simplifying the accounting for income taxes by removing certain exceptions in ASC 740 and providing simplification amendments. The guidance removes exceptions on intraperiod tax allocations and reporting and provides simplification on accounting for franchise taxes, tax basis goodwill and tax law changes. The guidance will be effective for the Company on January 1, 2021, with early adoption permitted. Transition requirements vary among the exceptions and amendments which include retrospective, modified retrospective and prospective application. The Company has evaluated the effects of the new guidance and does not expect the guidance to have a material impact on its results of operations, financial position, cash flows or disclosures. ASU 2020-04 - Reference Rate Reform In March 2020, the FASB issued optional guidance to ease the facilitation of the effects of reference rate reform on financial reporting. The guidance applies to certain contract modifications, hedging relationships and other transactions that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. LIBOR is expected to be retired with a full phase-out by the end of 2021 and replaced by a new reference rate, which includes SOFR. The guidance can be applied beginning in the interim period that includes March 12, 2020, and cannot be applied to contract modifications or hedging relationships entered into or evaluated after December 31, 2022. The Company is currently updating its credit agreements to include language regarding the successor or alternate rate to LIBOR. 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)	9 Months Ended
	Sep. 30, 2020
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 8. The Company's trade accounts receivable 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 and general economic conditions of the various local economies, 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)	9 Months Ended
	Sep. 30, 2020
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 common share (Poli

Earnings per common share (Policies)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Earnings per common 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 nonvested 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)	9 Months Ended
	Sep. 30, 2020
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)	9 Months Ended
	Sep. 30, 2020
Business Combinations [Abstract]
Business Combinations Policy [Policy Text Block]	The following acquisitions were accounted for as business combinations in accordance with ASC 805 - Business Combinations. The results of the acquired businesses have been included in the Consolidated Financial Statements beginning on the acquisition date. Pro forma financial amounts reflecting the effects of the business combinations are not presented, as none of these business combinations were material to the Company's financial position or results of operations. For all business combinations, the Company preliminarily allocates the purchase price of the acquisitions to the assets acquired and liabilities assumed based on their estimated fair values as of the acquisition dates and are considered provisional until final fair values are determined or the measurement period has passed. The Company expects to record adjustments as it accumulates the information needed to estimate the fair value of assets acquired and liabilities assumed, including working capital balances; identifiable intangible assets; property, plant and equipment; total consideration and goodwill. The excess of the purchase price over the aggregate fair values is recorded as goodwill. The Company calculated the fair value of the assets acquired in 2020 and 2019 using a market or cost approach (or a combination of both). Fair values for some of the assets were determined based on Level 3 inputs including estimated future cash flows, discount rates, growth rates, sales projections, retention rates and terminal

Fair value disclosures (Policie

Fair value disclosures (Policies)	9 Months Ended
	Sep. 30, 2020
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)	9 Months Ended
	Sep. 30, 2020
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)	9 Months Ended
	Sep. 30, 2020
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)	9 Months Ended
	Sep. 30, 2020
Credit Loss [Abstract]
Financing 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 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 Current expected credit loss provision 435 811 2 728 1,635 3,611 Less write-offs charged against the allowance 269 692 — 229 117 1,307 Credit loss recoveries collected 75 203 — — — 278 At September 30, 2020 $ 900 $ 1,853 $ 2 $ 6,124 $ 4,793 $ 13,672

Inventories and natural gas i_3

Inventories and natural gas in storage (Tables)	9 Months Ended
	Sep. 30, 2020
Inventory Disclosure [Abstract]
Inventories	Inventories on the Consolidated Balance Sheets were as follows: September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Aggregates held for resale $ 168,132 $ 143,157 $ 147,723 Asphalt oil 27,587 39,269 41,912 Materials and supplies 26,609 25,696 22,512 Merchandise for resale 21,525 23,902 22,232 Natural gas in storage (current) 27,135 32,164 22,058 Other 15,235 21,869 21,970 Total $ 286,223 $ 286,057 $ 278,407

Earnings per common share (Tabl

Earnings per common share (Tables)	9 Months Ended
	Sep. 30, 2020
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 Nine Months Ended September 30, September 30, 2020 2019 2020 2019 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 200,522 199,343 200,495 198,016 Effect of dilutive performance share awards and restricted stock units 97 40 20 17 Weighted average common shares outstanding - diluted 200,619 199,383 200,515 198,033 Shares excluded from the calculation of diluted earnings per share 87 155 139 243 Dividends declared per common share $ .2075 $ .2025 $ .6225 $ .6075

Accumulated other comprehensi_2

Accumulated other comprehensive income (loss) (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2019 $ (1,430) $ (40,734) $ 62 $ (42,102) Other comprehensive income before reclassifications — — 135 135 Amounts reclassified (to) from accumulated other comprehensive loss 111 462 (1) 572 Net current-period other comprehensive income 111 462 134 707 At March 31, 2020 $ (1,319) $ (40,272) $ 196 $ (41,395) 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) Other comprehensive loss before reclassifications — — (50) (50) Amounts reclassified from accumulated other comprehensive loss 111 471 28 610 Net current-period other comprehensive income (loss) 111 471 (22) 560 At September 30, 2020 $ (1,096) $ (39,321) $ 168 $ (40,249) Net Unrealized Postretirement Net Unrealized Total (In thousands) At December 31, 2018 $ (2,161) $ (36,069) $ (112) $ (38,342) Other comprehensive income before reclassifications — — 39 39 Amounts reclassified from accumulated other comprehensive loss 397 310 28 735 Net current-period other comprehensive income 397 310 67 774 At March 31, 2019 $ (1,764) $ (35,759) $ (45) $ (37,568) Other comprehensive income before reclassifications — — 79 79 Amounts reclassified from accumulated other comprehensive loss 111 276 12 399 Net current-period other comprehensive income 111 276 91 478 At June 30, 2019 $ (1,653) $ (35,483) $ 46 $ (37,090) Other comprehensive income before reclassifications — — 12 12 Amounts reclassified (to) from accumulated other comprehensive loss 112 292 (4) 400 Net current-period other comprehensive income 112 292 8 412 At September 30, 2019 $ (1,541) $ (35,191) $ 54 $ (36,678)
Reclassification out of accumulated other comprehensive loss	The following amounts were reclassified between accumulated other comprehensive loss and 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 Nine Months Ended Location on Consolidated September 30, September 30, 2020 2019 2020 2019 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ (148) $ (148) $ (443) $ (443) Interest expense 37 36 109 (177) Income taxes (111) (112) (334) (620) Amortization of postretirement liability losses included in net periodic benefit cost (623) (387) (1,869) (1,162) Other income 152 95 456 284 Income taxes (471) (292) (1,413) (878) Reclassification adjustment on available-for-sale investments included in net income (35) 5 (43) (46) Other income 7 (1) 9 10 Income taxes (28) 4 (34) (36) Total reclassifications $ (610) $ (400) $ (1,781) $ (1,534)

Revenue from contracts with c_3

Revenue from contracts with customers (Tables)	9 Months Ended
	Sep. 30, 2020
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 16. Three Months Ended September 30, 2020 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 33,086 $ 48,399 $ — $ — $ — $ — $ 81,485 Commercial utility sales 35,688 28,731 — — — — 64,419 Industrial utility sales 8,428 4,454 — — — — 12,882 Other utility sales 1,779 — — — — — 1,779 Natural gas transportation — 11,159 27,583 — — — 38,742 Natural gas gathering — — 973 — — — 973 Natural gas storage — — 3,885 — — — 3,885 Contracting services — — — 448,569 — — 448,569 Construction materials — — — 608,673 — — 608,673 Intrasegment eliminations — — — (234,693) — — (234,693) Inside specialty contracting — — — — 352,845 — 352,845 Outside specialty contracting — — — — 187,202 — 187,202 Other 7,663 2,590 3,203 — 486 3,030 16,972 Intersegment eliminations (195) (185) (3,622) (110) (425) (3,006) (7,543) Revenues from contracts with customers 86,449 95,148 32,022 822,439 540,108 24 1,576,190 Revenues out of scope 998 (445) 46 — 10,500 — 11,099 Total external operating revenues $ 87,447 $ 94,703 $ 32,068 $ 822,439 $ 550,608 $ 24 $ 1,587,289 Three Months Ended September 30, 2019 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 30,376 $ 44,902 $ — $ — $ — $ — $ 75,278 Commercial utility sales 36,670 29,148 — — — — 65,818 Industrial utility sales 9,348 4,307 — — — — 13,655 Other utility sales 1,862 — — — — — 1,862 Natural gas transportation — 11,410 25,229 — — — 36,639 Natural gas gathering — — 2,510 — — — 2,510 Natural gas storage — — 3,044 — — — 3,044 Contracting services — — — 461,716 — — 461,716 Construction materials — — — 638,862 — — 638,862 Intrasegment eliminations — — — (231,078) — — (231,078) Inside specialty contracting — — — — 317,202 — 317,202 Outside specialty contracting — — — — 151,285 — 151,285 Other 9,380 2,708 5,534 — 45 2,884 20,551 Intersegment eliminations — — (3,831) (124) (1,226) (2,862) (8,043) Revenues from contracts with customers 87,636 92,475 32,486 869,376 467,306 22 1,549,301 Revenues out of scope 2,209 1,167 47 — 11,075 — 14,498 Total external operating revenues $ 89,845 $ 93,642 $ 32,533 $ 869,376 $ 478,381 $ 22 $ 1,563,799 Nine Months Ended September 30, 2020 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 93,389 $ 313,753 $ — $ — $ — $ — $ 407,142 Commercial utility sales 99,152 184,754 — — — — 283,906 Industrial utility sales 26,867 18,633 — — — — 45,500 Other utility sales 5,018 — — — — — 5,018 Natural gas transportation — 33,307 82,980 — — — 116,287 Natural gas gathering — — 4,244 — — — 4,244 Natural gas storage — — 10,035 — — — 10,035 Contracting services — — — 850,326 — — 850,326 Construction materials — — — 1,299,081 — — 1,299,081 Intrasegment eliminations — — — (443,516) — — (443,516) Inside specialty contracting — — — — 1,049,975 — 1,049,975 Outside specialty contracting — — — — 478,047 — 478,047 Other 23,830 7,800 9,807 — 1,249 8,882 51,568 Intersegment eliminations (586) (555) (36,820) (262) (3,674) (8,952) (50,849) Revenues from contracts with customers 247,670 557,692 70,246 1,705,629 1,525,597 (70) 4,106,764 Revenues out of scope 2,123 4,949 135 — 33,620 — 40,827 Total external operating revenues $ 249,793 $ 562,641 $ 70,381 $ 1,705,629 $ 1,559,217 $ (70) $ 4,147,591 Nine Months Ended September 30, 2019 Electric Natural gas Pipeline Construction Construction Other Total (In thousands) Residential utility sales $ 93,368 $ 316,521 $ — $ — $ — $ — $ 409,889 Commercial utility sales 105,572 192,191 — — — — 297,763 Industrial utility sales 27,576 18,495 — — — — 46,071 Other utility sales 5,540 — — — — — 5,540 Natural gas transportation — 33,686 75,091 — — — 108,777 Natural gas gathering — — 7,027 — — — 7,027 Natural gas storage — — 8,313 — — — 8,313 Contracting services — — — 841,881 — — 841,881 Construction materials — — — 1,262,938 — — 1,262,938 Intrasegment eliminations — — — (412,144) — — (412,144) Inside specialty contracting — — — — 936,008 — 936,008 Outside specialty contracting — — — — 391,971 — 391,971 Other 26,918 9,544 14,523 — 70 13,631 64,686 Intersegment eliminations — — (35,298) (388) (2,076) (13,566) (51,328) Revenues from contracts with customers 258,974 570,437 69,656 1,692,287 1,325,973 65 3,917,392 Revenues out of scope 4,449 (781) 171 — 37,332 — 41,171 Total external operating revenues $ 263,423 $ 569,656 $ 69,827 $ 1,692,287 $ 1,363,305 $ 65 $ 3,958,563
Contract balances	The changes in contract assets and liabilities were as follows: September 30, 2020 December 31, 2019 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 135,958 $ 109,078 $ 26,880 Receivables, net Contract liabilities - current (158,923) (142,768) (16,155) Accounts payable Contract liabilities - noncurrent (62) (19) (43) Noncurrent liabilities - other Net contract liabilities $ (23,027) $ (33,709) $ 10,682

Goodwill and other intangible_2

Goodwill and other intangible assets (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020 Goodwill Measurement Balance at September 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 24,436 400 143,224 Total $ 681,358 $ 30,919 $ 400 $ 712,677 Balance at January 1, 2019 Goodwill Measurement Balance at September 30, 2019 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 209,421 14,473 (6,669) 217,225 Construction services 109,765 8,623 — 118,388 Total $ 664,922 $ 23,096 $ (6,669) $ 681,349 Balance at January 1, 2019 Goodwill Measurement Balance at December 31, 2019 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 209,421 14,482 (6,669) 217,234 Construction services 109,765 8,623 — 118,388 Total $ 664,922 $ 23,105 $ (6,669) $ 681,358
Other amortizable intangible assets	Other amortizable intangible assets were as follows: September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Customer relationships $ 27,551 $ 18,011 $ 17,958 Less accumulated amortization 5,958 5,823 6,268 21,593 12,188 11,690 Noncompete agreements 3,941 3,419 3,439 Less accumulated amortization 2,176 1,868 1,957 1,765 1,551 1,482 Other 12,853 7,488 8,094 Less accumulated amortization 9,835 5,716 6,020 3,018 1,772 2,074 Total $ 26,376 $ 15,511 $ 15,246
Estimated amortization expense	Estimated amortization expense for identifiable intangible assets as of September 30, 2020, was: Remainder of 2021 2022 2023 2024 Thereafter (In thousands) Amortization expense $ 2,462 $ 4,579 $ 4,108 $ 3,975 $ 3,653 $ 7,599

Regulatory assets and liabili_2

Regulatory assets and liabilities (Tables)	9 Months Ended
	Sep. 30, 2020
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	The following table summarizes the individual components of unamortized regulatory assets and liabilities: Estimated * September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 48,478 $ 39,383 $ 42,823 Cost recovery mechanisms Up to 1 year 8,177 8,706 6,288 Conservation programs Up to 1 year 7,857 7,776 6,963 Other Up to 1 year 14,613 13,316 7,539 79,125 69,181 63,613 Noncurrent: Pension and postretirement benefits ** 157,015 165,843 157,069 Asset retirement obligations Over plant lives 68,815 64,771 66,000 Plant to be retired - 57,499 26,152 32,931 Manufactured gas plant site remediation - 25,964 15,510 15,126 Natural gas costs recoverable through rate adjustments Up to 3 years 24,677 53,618 46,381 Cost recovery mechanisms Up to 10 years 14,281 12,206 13,108 Taxes recoverable from customers Over plant lives 10,847 11,600 11,486 Long-term debt refinancing costs Up to 17 years 3,826 4,439 4,286 Other Up to 19 years 6,840 8,660 7,397 369,764 362,799 353,784 Total regulatory assets $ 448,889 $ 431,980 $ 417,397 Regulatory liabilities: Current: Natural gas costs refundable through rate adjustments $ 20,556 $ 19,194 $ 23,825 Electric fuel and purchased power deferral 6,171 2,040 5,824 Taxes refundable to customers 4,223 4,309 3,472 Other 8,887 11,402 9,814 39,837 36,945 42,935 Noncurrent: Taxes refundable to customers 232,186 253,703 246,034 Plant removal and decommissioning costs 173,367 174,595 173,722 Pension and postretirement benefits 17,991 15,190 18,065 Other 11,392 10,272 9,549 434,936 453,760 447,370 Total regulatory liabilities $ 474,773 $ 490,705 $ 490,305 Net regulatory position $ (25,884) $ (58,725) $ (72,908) * Estimated recovery period for regulatory assets currently being recovered in rates charged to customers. ** Recovered as expense is incurred or cash contributions are made.
Regulatory Liabilities	The following table summarizes the individual components of unamortized regulatory assets and liabilities: Estimated * September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Regulatory assets: Current: Natural gas costs recoverable through rate adjustments Up to 1 year $ 48,478 $ 39,383 $ 42,823 Cost recovery mechanisms Up to 1 year 8,177 8,706 6,288 Conservation programs Up to 1 year 7,857 7,776 6,963 Other Up to 1 year 14,613 13,316 7,539 79,125 69,181 63,613 Noncurrent: Pension and postretirement benefits ** 157,015 165,843 157,069 Asset retirement obligations Over plant lives 68,815 64,771 66,000 Plant to be retired - 57,499 26,152 32,931 Manufactured gas plant site remediation - 25,964 15,510 15,126 Natural gas costs recoverable through rate adjustments Up to 3 years 24,677 53,618 46,381 Cost recovery mechanisms Up to 10 years 14,281 12,206 13,108 Taxes recoverable from customers Over plant lives 10,847 11,600 11,486 Long-term debt refinancing costs Up to 17 years 3,826 4,439 4,286 Other Up to 19 years 6,840 8,660 7,397 369,764 362,799 353,784 Total regulatory assets $ 448,889 $ 431,980 $ 417,397 Regulatory liabilities: Current: Natural gas costs refundable through rate adjustments $ 20,556 $ 19,194 $ 23,825 Electric fuel and purchased power deferral 6,171 2,040 5,824 Taxes refundable to customers 4,223 4,309 3,472 Other 8,887 11,402 9,814 39,837 36,945 42,935 Noncurrent: Taxes refundable to customers 232,186 253,703 246,034 Plant removal and decommissioning costs 173,367 174,595 173,722 Pension and postretirement benefits 17,991 15,190 18,065 Other 11,392 10,272 9,549 434,936 453,760 447,370 Total regulatory liabilities $ 474,773 $ 490,705 $ 490,305 Net regulatory position $ (25,884) $ (58,725) $ (72,908) * Estimated recovery period for regulatory assets currently being recovered in rates charged to customers. ** Recovered as expense is incurred or cash contributions are made.

Fair value measurements (Tables

Fair value measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Available-for-sale securities	Details of available-for-sale securities were as follows: September 30, 2020 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,813 $ 213 $ 4 $ 10,022 U.S. Treasury securities 1,166 3 — 1,169 Total $ 10,979 $ 216 $ 4 $ 11,191 September 30, 2019 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,577 $ 86 $ 16 $ 9,647 U.S. Treasury securities 1,258 — 1 1,257 Total $ 10,835 $ 86 $ 17 $ 10,904 December 31, 2019 Cost Gross Gross Fair Value (In thousands) Mortgage-backed securities $ 9,804 $ 87 $ 10 $ 9,881 U.S. Treasury securities 1,228 1 — 1,229 Total $ 11,032 $ 88 $ 10 $ 11,110
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 September 30, 2020, Using Quoted Prices in Significant Significant Balance at September 30, 2020 (In thousands) Assets: Money market funds $ — $ 8,478 $ — $ 8,478 Insurance contract* — 95,687 — 95,687 Available-for-sale securities: Mortgage-backed securities — 10,022 — 10,022 U.S. Treasury securities — 1,169 — 1,169 Total assets measured at fair value $ — $ 115,356 $ — $ 115,356 * The insurance contract invests approximately 68 percent in fixed-income investments, 15 percent in common stock of large-cap companies, 6 percent in common stock of mid-cap companies, 6 percent in common stock of small-cap companies, 4 percent in target date investments and 1 percent in cash equivalents. Fair Value Measurements at September 30, 2019, Using Quoted Prices in Significant Significant Balance at September 30, 2019 (In thousands) Assets: Money market funds $ — $ 7,472 $ — $ 7,472 Insurance contract* — 84,222 — 84,222 Available-for-sale securities: Mortgage-backed securities — 9,647 — 9,647 U.S. Treasury securities — 1,257 — 1,257 Total assets measured at fair value $ — $ 102,598 $ — $ 102,598 * The insurance contract invests approximately 53 percent in fixed-income investments, 21 percent in common stock of large-cap companies, 11 percent in common stock of mid-cap companies, 10 percent in common stock of small-cap companies, 3 percent in target date investments and 2 percent in cash equivalents. Fair Value Measurements at December 31, 2019, Using Quoted Prices in Significant Significant Balance at December 31, 2019 (In thousands) Assets: Money market funds $ — $ 8,440 $ — $ 8,440 Insurance contract* — 87,009 — 87,009 Available-for-sale securities: Mortgage-backed securities — 9,881 — 9,881 U.S. Treasury securities — 1,229 — 1,229 Total assets measured at fair value $ — $ 106,559 $ — $ 106,559 * The insurance contract invests approximately 51 percent in fixed-income investments, 23 percent in common stock of large-cap companies, 12 percent in common stock of mid-cap companies, 10 percent in common stock of small-cap companies, 3 percent in target date investments and 1 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: September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Carrying amount $ 2,270,290 $ 2,246,756 $ 2,243,107 Fair value $ 2,593,743 $ 2,450,209 $ 2,418,631

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Long-term debt outstanding	Long-term debt outstanding was as follows: Weighted September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Senior Notes due on dates ranging from October 22, 2022 to June 15, 2060 4.43 % $ 1,900,000 $ 1,655,000 $ 1,850,000 Commercial paper supported by revolving credit agreements 0.44 % 214,150 281,800 222,900 Term Loan Agreement due on September 3, 2032 2.00 % 8,400 209,100 9,100 Credit agreements due on June 7, 2024 2.40 % 91,000 31,000 89,050 Medium-Term Notes due on dates ranging from September 15, 2027 to March 16, 2029 7.32 % 35,000 50,000 50,000 Other notes due on dates ranging from July 15, 2021 to November 30, 2038 4.60 % 28,284 26,083 29,117 Less unamortized debt issuance costs 6,526 6,074 7,010 Less discount 18 153 50 Total long-term debt 2,270,290 2,246,756 2,243,107 Less current maturities 1,558 65,810 16,540 Net long-term debt $ 2,268,732 $ 2,180,946 $ 2,226,567
Schedule of debt maturities	Long-term debt maturities, which excludes unamortized debt issuance costs and discount, at September 30, 2020, were as follows: Remainder of 2021 2022 2023 2024 Thereafter (In thousands) Long-term debt maturities $ 28 $ 1,528 $ 148,038 $ 77,921 $ 366,571 $ 1,682,748

Cash flow information (Tables)

Cash flow information (Tables)	9 Months Ended
	Sep. 30, 2020
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: Nine Months Ended September 30, 2020 2019 (In thousands) Interest, net* $ 63,086 $ 64,596 Income taxes paid, net** $ 43,448 $ 1,816 * AFUDC - borrowed was $2.0 million for the nine months ended September 30, 2020 and 2019. ** Income taxes paid, including discontinued operations, were $43.5 million and $2.0 million for the nine months ended September 30, 2020 and 2019, respectively. Noncash investing and financing transactions were as follows: September 30, 2020 September 30, 2019 December 31, 2019 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 41,315 $ 46,770 $ 54,880 Property, plant and equipment additions in accounts payable $ 33,240 $ 34,368 $ 46,119 Accrual for holdback payment related to a business combination $ 5,000 $ — $ — Debt assumed in connection with a business combination $ — $ 1,163 $ 1,163

Business segment data (Tables)

Business segment data (Tables)	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Information on the Company's businesses	Information on the Company's segments was as follows: Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 (In thousands) External operating revenues: Regulated operations: Electric $ 87,447 $ 89,845 $ 249,793 $ 263,423 Natural gas distribution 94,703 93,642 562,641 569,656 Pipeline 27,965 25,957 57,717 52,230 210,115 209,444 870,151 885,309 Non-regulated operations: Pipeline 4,103 6,576 12,664 17,597 Construction materials and contracting 822,439 869,376 1,705,629 1,692,287 Construction services 550,608 478,381 1,559,217 1,363,305 Other 24 22 (70) 65 1,377,174 1,354,355 3,277,440 3,073,254 Total external operating revenues $ 1,587,289 $ 1,563,799 $ 4,147,591 $ 3,958,563 Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 (In thousands) Intersegment operating revenues: Regulated operations: Electric $ 195 $ — $ 586 $ — Natural gas distribution 185 — 555 — Pipeline 3,543 3,750 36,583 35,098 3,923 3,750 37,724 35,098 Non-regulated operations: Pipeline 79 81 237 200 Construction materials and contracting 110 124 262 388 Construction services 425 1,226 3,674 2,076 Other 3,006 2,862 8,952 13,566 3,620 4,293 13,125 16,230 Intersegment eliminations (7,543) (8,043) (50,849) (51,328) Total intersegment operating revenues $ — $ — $ — $ — Operating income (loss): Electric $ 21,159 $ 21,930 $ 48,827 $ 49,708 Natural gas distribution (18,393) (15,565) 32,285 32,132 Pipeline 11,762 11,416 35,406 32,017 Construction materials and contracting 148,522 143,024 179,994 147,622 Construction services 40,507 29,950 102,185 89,381 Other 154 (1,285) 339 140 Total operating income $ 203,711 $ 189,470 $ 399,036 $ 351,000 Net income (loss): Regulated operations: Electric $ 16,787 $ 16,291 $ 40,314 $ 39,267 Natural gas distribution (17,614) (15,625) 13,795 14,623 Pipeline 7,812 6,933 23,882 20,316 6,985 7,599 77,991 74,206 Non-regulated operations: Pipeline 189 801 444 1,380 Construction materials and contracting 107,307 102,611 122,113 97,328 Construction services 29,789 21,113 74,544 63,982 Other 8,745 4,004 3,303 3,466 146,030 128,529 200,404 166,156 Income from continuing operations 153,015 136,128 278,395 240,362 Income (loss) from discontinued operations, net of tax 63 1,509 (484) 26 Net income $ 153,078 $ 137,637 $ 277,911 $ 240,388

Employee benefit plans (Tables)

Employee benefit plans (Tables)	9 Months Ended
	Sep. 30, 2020
Retirement Benefits [Abstract]
Schedule of net benefit costs	Components of net periodic benefit cost (credit) for the Company's pension and other postretirement benefit plans were as follows: Pension Benefits Other Three Months Ended September 30, 2020 2019 2020 2019 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 383 $ 286 Interest cost 3,023 3,806 609 746 Expected return on assets (4,987) (4,559) (1,115) (1,201) Amortization of prior service credit — — (349) (289) Amortization of net actuarial loss 1,793 1,387 71 27 Net periodic benefit cost (credit), including amount capitalized (171) 634 (401) (431) Less amount capitalized — — 39 26 Net periodic benefit cost (credit) $ (171) $ 634 $ (440) $ (457) Pension Benefits Other Nine Months Ended September 30, 2020 2019 2020 2019 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 1,149 $ 857 Interest cost 9,070 11,419 1,827 2,239 Expected return on assets (14,962) (13,677) (3,764) (3,603) Amortization of prior service credit — — (1,048) (866) Amortization of net actuarial loss 5,379 4,160 215 82 Net periodic benefit cost (credit), including amount capitalized (513) 1,902 (1,621) (1,291) Less amount capitalized — — 106 84 Net periodic benefit cost (credit) $ (513) $ 1,902 $ (1,727) $ (1,375)

Basis of Presentation (Details)

Basis of Presentation (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues	$ 1,587,289			$ 1,563,799			$ 4,147,591	$ 3,958,563
Operating Expenses	1,383,578			1,374,329			3,748,555	3,607,563
Net income	153,078	$ 99,703	$ 25,130	137,637	$ 61,825	$ 40,926	277,911	240,388
Receivables, net	$ 1,009,433			$ 968,279			$ 1,009,433	$ 968,279	$ 836,605
Restatement Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues			(7,700)
Operating Expenses			(1,200)
Net income			(6,700)
Accounts Payable			(1,200)
Receivables, net			$ (7,700)

Receivables and allowance for_3

Receivables and allowance for expected credit losses (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Credit Loss [Abstract]
Receivables past due 90 days or more	$ 48.9	$ 46.7	$ 56

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
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	$ 11,090	$ 11,125	$ 8,497
Current expected credit loss provision	3,611	1,075	3,555
Less write-offs charged against the allowance	1,307	1,399	1,265
Credit loss recoveries collected	278	289	338
Balance	13,672	11,090	11,125
Electric
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	659	492	328
Current expected credit loss provision	435	303	555
Less write-offs charged against the allowance	269	224	500
Credit loss recoveries collected	75	88	109
Balance	900	659	492
Natural gas distribution
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	1,531	1,817	1,056
Current expected credit loss provision	811	190	1,156
Less write-offs charged against the allowance	692	677	624
Credit loss recoveries collected	203	201	229
Balance	1,853	1,531	1,817
Pipeline
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	0	0	0
Current expected credit loss provision	2	0	0
Less write-offs charged against the allowance	0	0	0
Credit loss recoveries collected	0	0	0
Balance	2	0	0
Construction materials and contracting
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	5,625	5,983	5,357
Current expected credit loss provision	728	(314)	694
Less write-offs charged against the allowance	229	44	68
Credit loss recoveries collected	0	0	0
Balance	6,124	5,625	5,983
Construction services
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance	3,275	2,833	1,756
Current expected credit loss provision	1,635	896	1,150
Less write-offs charged against the allowance	117	454	73
Credit loss recoveries collected	0	0	0
Balance	$ 4,793	$ 3,275	$ 2,833

Allowance for doubtful accounts

Allowance for doubtful accounts (Details 3) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019
Receivables [Abstract]
Accounts Receivable, Allowance for Credit Loss	$ 13,672	$ 11,090	$ 11,125	$ 8,497	$ 8,700

Inventories and natural gas i_4

Inventories and natural gas in storage (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Inventory Disclosure [Abstract]
Aggregates held for resale	$ 168,132	$ 147,723	$ 143,157
Asphalt oil	27,587	41,912	39,269
Materials and supplies	26,609	22,512	25,696
Merchandise for resale	21,525	22,232	23,902
Natural gas in storage (current)	27,135	22,058	32,164
Other	15,235	21,970	21,869
Total	286,223	278,407	286,057
Natural gas in storage noncurrent	$ 48,300	$ 48,400	$ 48,200

Earnings per common share (Deta

Earnings per common share (Details) - $ / shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	200,522	199,343	200,495	198,016
Effect of dilutive performance share awards and restricted stock units	97	40	20	17
Weighted average common shares outstanding - diluted	200,619	199,383	200,515	198,033
Shares excluded from the calculation of diluted earnings per share	87	155	139	243
Dividends declared per common share	$ 0.2075	$ 0.2025	$ 0.6225	$ 0.6075

Accumulated other comprehensi_3

Accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	$ 2,897,687	$ 2,836,592	$ 2,847,246	$ 2,660,301	$ 2,605,692	$ 2,566,775	$ 2,847,246	$ 2,566,775
Other comprehensive income (loss)	560	586	707	412	478	774	1,853	1,664
Balance	3,012,765	2,897,687	2,836,592	2,795,606	2,660,301	2,605,692	3,012,765	2,795,606
Net unrealized gain (loss) on derivative instruments qualifying as hedges
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(1,207)	(1,319)	(1,430)	(1,653)	(1,764)	(2,161)	(1,430)	(2,161)
Other comprehensive income (loss) before reclassifications	0	0	0	0	0	0
Amounts reclassified (to) from accumulated other comprehensive loss	111	112	111	112	111	397
Other comprehensive income (loss)	111	112	111	112	111	397
Balance	(1,096)	(1,207)	(1,319)	(1,541)	(1,653)	(1,764)	(1,096)	(1,541)
Postretirement liability adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(39,792)	(40,272)	(40,734)	(35,483)	(35,759)	(36,069)	(40,734)	(36,069)
Other comprehensive income (loss) before reclassifications	0	0	0	0	0	0
Amounts reclassified (to) from accumulated other comprehensive loss	471	480	462	292	276	310
Other comprehensive income (loss)	471	480	462	292	276	310
Balance	(39,321)	(39,792)	(40,272)	(35,191)	(35,483)	(35,759)	(39,321)	(35,191)
Net unrealized gain (loss) on available-for-sale investments
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	190	196	62	46	(45)	(112)	62	(112)
Other comprehensive income (loss) before reclassifications	(50)	(13)	135	12	79	39
Amounts reclassified (to) from accumulated other comprehensive loss	28	7	(1)	(4)	12	28
Other comprehensive income (loss)	(22)	(6)	134	8	91	67
Balance	168	190	196	54	46	(45)	168	54
Total accumulated other comprehensive loss
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(40,809)	(41,395)	(42,102)	(37,090)	(37,568)	(38,342)	(42,102)	(38,342)
Other comprehensive income (loss) before reclassifications	(50)	(13)	135	12	79	39
Amounts reclassified (to) from accumulated other comprehensive loss	610	599	572	400	399	735
Other comprehensive income (loss)	560	586	707	412	478	774
Balance	$ (40,249)	$ (40,809)	$ (41,395)	$ (36,678)	$ (37,090)	$ (37,568)	$ (40,249)	$ (36,678)

Reclassification out of accumul

Reclassification out of accumulated other comprehensive income (loss) (Details 2) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Interest expense	$ (23,761)			$ (25,258)			$ (73,132)	$ (74,094)
Income taxes	(31,547)			(31,098)			(61,178)	(48,766)
Other income	4,612			3,014			13,669	12,222
Net Income	153,078	$ 99,703	$ 25,130	137,637	$ 61,825	$ 40,926	277,911	240,388
Reclassification out of accumulated other comprehensive income
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Net Income	(610)			(400)			(1,781)	(1,534)
Reclassification adjustment for loss on derivative instruments included in net income | Reclassification out of accumulated other comprehensive income | Interest rate contract
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Interest expense	(148)			(148)			(443)	(443)
Income taxes	37			36			109	(177)
Net Income	(111)			(112)			(334)	(620)
Amortization of postretirement liability losses included in net periodic benefit cost | Reclassification out of accumulated other comprehensive income
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Income taxes	152			95			456	284
Other income	(623)			(387)			(1,869)	(1,162)
Net Income	(471)			(292)			(1,413)	(878)
Reclassification adjustment on available-for-sale investments included in net income | Reclassification out of accumulated other comprehensive income
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Income taxes	7			(1)			9	10
Other income	(35)			5			(43)	(46)
Net Income	$ (28)			$ 4			$ (34)	$ (36)

Disaggregation of revenue (Deta

Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 1,587,289	$ 1,563,799	$ 4,147,591	$ 3,958,563
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(7,543)	(8,043)	(50,849)	(51,328)
Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(234,693)	(231,078)	(443,516)	(412,144)
Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues	38,742	36,639	116,287	108,777
Natural gas gathering
Disaggregation of Revenue [Line Items]
Revenues	973	2,510	4,244	7,027
Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues	3,885	3,044	10,035	8,313
Contracting services
Disaggregation of Revenue [Line Items]
Revenues	448,569	461,716	850,326	841,881
Construction materials
Disaggregation of Revenue [Line Items]
Revenues	608,673	638,862	1,299,081	1,262,938
Inside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	352,845	317,202	1,049,975	936,008
Outside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	187,202	151,285	478,047	391,971
Other
Disaggregation of Revenue [Line Items]
Revenues	16,972	20,551	51,568	64,686
Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	1,576,190	1,549,301	4,106,764	3,917,392
Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	11,099	14,498	40,827	41,171
Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	81,485	75,278	407,142	409,889
Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	64,419	65,818	283,906	297,763
Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	12,882	13,655	45,500	46,071
Other utility sales
Disaggregation of Revenue [Line Items]
Revenues	1,779	1,862	5,018	5,540
Electric
Disaggregation of Revenue [Line Items]
Revenues	87,447	89,845	249,793	263,423
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(195)	0	(586)	0
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	7,663	9,380	23,830	26,918
Electric | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	86,449	87,636	247,670	258,974
Electric | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	998	2,209	2,123	4,449
Electric | Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	33,086	30,376	93,389	93,368
Electric | Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	35,688	36,670	99,152	105,572
Electric | Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	8,428	9,348	26,867	27,576
Electric | Other utility sales
Disaggregation of Revenue [Line Items]
Revenues	1,779	1,862	5,018	5,540
Natural gas distribution
Disaggregation of Revenue [Line Items]
Revenues	94,703	93,642	562,641	569,656
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(185)	0	(555)	0
Natural gas distribution | Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues	11,159	11,410	33,307	33,686
Natural gas distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	2,590	2,708	7,800	9,544
Natural gas distribution | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	95,148	92,475	557,692	570,437
Natural gas distribution | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	(445)	1,167	4,949	(781)
Natural gas distribution | Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	48,399	44,902	313,753	316,521
Natural gas distribution | Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	28,731	29,148	184,754	192,191
Natural gas distribution | Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	4,454	4,307	18,633	18,495
Natural gas distribution | Other utility sales
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Pipeline
Disaggregation of Revenue [Line Items]
Revenues	32,068	32,533	70,381	69,827
Pipeline | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(3,622)	(3,831)	(36,820)	(35,298)
Pipeline | Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues	27,583	25,229	82,980	75,091
Pipeline | Natural gas gathering
Disaggregation of Revenue [Line Items]
Revenues	973	2,510	4,244	7,027
Pipeline | Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues	3,885	3,044	10,035	8,313
Pipeline | Other
Disaggregation of Revenue [Line Items]
Revenues	3,203	5,534	9,807	14,523
Pipeline | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	32,022	32,486	70,246	69,656
Pipeline | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	46	47	135	171
Construction materials and contracting
Disaggregation of Revenue [Line Items]
Revenues	822,439	869,376	1,705,629	1,692,287
Construction materials and contracting | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(110)	(124)	(262)	(388)
Construction materials and contracting | Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(234,693)	(231,078)	(443,516)	(412,144)
Construction materials and contracting | Contracting services
Disaggregation of Revenue [Line Items]
Revenues	448,569	461,716	850,326	841,881
Construction materials and contracting | Construction materials
Disaggregation of Revenue [Line Items]
Revenues	608,673	638,862	1,299,081	1,262,938
Construction materials and contracting | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Construction materials and contracting | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	822,439	869,376	1,705,629	1,692,287
Construction materials and contracting | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Construction services
Disaggregation of Revenue [Line Items]
Revenues	550,608	478,381	1,559,217	1,363,305
Construction services | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(425)	(1,226)	(3,674)	(2,076)
Construction services | Inside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	352,845	317,202	1,049,975	936,008
Construction services | Outside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	187,202	151,285	478,047	391,971
Construction services | Other
Disaggregation of Revenue [Line Items]
Revenues	486	45	1,249	70
Construction services | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	540,108	467,306	1,525,597	1,325,973
Construction services | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	10,500	11,075	33,620	37,332
Other
Disaggregation of Revenue [Line Items]
Revenues	24	22	(70)	65
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(3,006)	(2,862)	(8,952)	(13,566)
Other | Other
Disaggregation of Revenue [Line Items]
Revenues	3,030	2,884	8,882	13,631
Other | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	24	22	(70)	65
Other | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 0	$ 0	$ 0

Contract balances (Details 2)

Contract balances (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Contract assets	$ 135,958		$ 135,958		$ 109,078
Change in contract assets			26,880
Contract liabilities - current	(158,923)		(158,923)		(142,768)
Change in contract liabilities - current			(16,155)
Contract liabilities - noncurrent	(62)		(62)		(19)
Change in contract liabilities - noncurrent			(43)
Net contract liabilities	(23,027)		(23,027)		$ (33,709)
Change in net contract liabilities			10,682
Amounts included in contract liability at the beginning of the period	15,600	$ 7,500	137,300	$ 86,500
Amounts from performance obligations satisfied in prior periods	$ 34,700	$ 21,800	$ 58,800	$ 40,300

Revenue from contracts with c_4

Revenue from contracts with customers Remaining performance obligations (Details 3) $ in Millions	Sep. 30, 2020USD ($)
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 2,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 1,500
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 265.6
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	24 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-10-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 260.6
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	25 months

Business Combinations (Details)

Business Combinations (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill	$ 712,677,000	$ 681,349,000	$ 681,358,000	$ 664,922,000
Measurement period adjustments	400,000	$ (6,669,000)	$ (6,669,000)
2020 Acquisition
Business Acquisition [Line Items]
Gross Aggregate Consideration	78,200,000
Cash Assumed	1,700,000
Business Combination, Consideration Transferred	71,500,000
Business Combination indemnity holdback liability	5,000,000
Current Assets	45,900,000
Property, Plant, and Equipment	4,900,000
Goodwill	31,300,000
Other Intangibles	17,600,000
Current Liabilities	21,200,000
Deferred Credits and Other Liabilities	300,000
Measurement period adjustments	$ 400,000

Business Combinations (Details

Business Combinations (Details 2) - USD ($)	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill	$ 681,358,000	$ 712,677,000	$ 681,349,000	$ 664,922,000
2019 Acquisition
Business Acquisition [Line Items]
Gross Aggregate Consideration	56,800,000
Debt Assumed	1,200,000
Current Assets	15,800,000
Property, Plant, and Equipment	16,700,000
Goodwill	23,100,000
Other Intangibles	6,700,000
Deferred Charges and Other Assets	500,000
Current Liabilities	5,900,000
Deferred Credits and Other Liabilities	$ 100,000

Lessor accounting (Details)

Lessor accounting (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Leases [Abstract]
Operating Lease, Lease Income	$ 10.7	$ 11.2	$ 34	$ 37.7
Lessor, Operating Lease, Payments to be Received, Next Twelve Months	$ 8.4		$ 8.4

Goodwill rollforward (Details)

Goodwill rollforward (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Goodwill [Roll Forward]
Balance at beginning of period	$ 681,358	$ 664,922	$ 664,922
Goodwill acquired during the year	30,919	23,096	23,105
Measurement period adjustments	400	(6,669)	(6,669)
Balance at end of period	712,677	681,349	681,358
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	217,234	209,421	209,421
Goodwill acquired during the year	6,483	14,473	14,482
Measurement period adjustments	0	(6,669)	(6,669)
Balance at end of period	223,717	217,225	217,234
Construction services
Goodwill [Roll Forward]
Balance at beginning of period	118,388	109,765	109,765
Goodwill acquired during the year	24,436	8,623	8,623
Measurement period adjustments	400	0	0
Balance at end of period	$ 143,224	$ 118,388	$ 118,388

Other intangible assets (Detail

Other intangible assets (Details 2) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 26,376,000	$ 15,511,000	$ 26,376,000	$ 15,511,000	$ 15,246,000
Amortization of intangible assets	2,100,000	500,000	6,800,000	1,600,000
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	27,551,000	18,011,000	27,551,000	18,011,000	17,958,000
Intangible assets, less accumulated amortization	5,958,000	5,823,000	5,958,000	5,823,000	6,268,000
Intangible assets, net (excluding goodwill)	21,593,000	12,188,000	21,593,000	12,188,000	11,690,000
Noncompete agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	3,941,000	3,419,000	3,941,000	3,419,000	3,439,000
Intangible assets, less accumulated amortization	2,176,000	1,868,000	2,176,000	1,868,000	1,957,000
Intangible assets, net (excluding goodwill)	1,765,000	1,551,000	1,765,000	1,551,000	1,482,000
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	12,853,000	7,488,000	12,853,000	7,488,000	8,094,000
Intangible assets, less accumulated amortization	9,835,000	5,716,000	9,835,000	5,716,000	6,020,000
Intangible assets, net (excluding goodwill)	$ 3,018,000	$ 1,772,000	$ 3,018,000	$ 1,772,000	$ 2,074,000

Future amortization expense (De

Future amortization expense (Details 3) $ in Thousands	Sep. 30, 2020USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Remainder of 2020	$ 2,462
2021	4,579
2022	4,108
2023	3,975
2024	3,653
Thereafter	$ 7,599

Regulatory assets and liabili_3

Regulatory assets and liabilities Regulatory Assets (Details 1) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Regulatory Assets [Line Items]
Regulatory Assets, Current	$ 79,125	$ 63,613	$ 69,181
Regulatory Assets, Noncurrent	369,764	353,784	362,799
Total regulatory assets	448,889	417,397	431,980
Regulatory assets not earning a rate of return	318,200	276,500	278,600
Natural gas costs recoverable through rate adjustments
Regulatory Assets [Line Items]
Regulatory Assets, Current	48,478	42,823	39,383
Regulatory Assets, Noncurrent	24,677	46,381	53,618
Cost recovery mechanisms
Regulatory Assets [Line Items]
Regulatory Assets, Current	8,177	6,288	8,706
Regulatory Assets, Noncurrent	$ 14,281	13,108	12,206
Conservation programs
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	Up to 1 year
Regulatory Assets, Current	$ 7,857	6,963	7,776
Pension and postretirement benefits
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	**
Regulatory Assets, Noncurrent	$ 157,015	157,069	165,843
Asset retirement obligations
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	Over plant lives
Regulatory Assets, Noncurrent	$ 68,815	66,000	64,771
Plant to be retired
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	-
Regulatory Assets, Noncurrent	$ 57,499	32,931	26,152
Manufactured gas plant site remediation
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	-
Regulatory Assets, Noncurrent	$ 25,964	15,126	15,510
Taxes recoverable from customers
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	Over plant lives
Regulatory Assets, Noncurrent	$ 10,847	11,486	11,600
Long-term debt refinancing costs
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	Up to 17 years
Regulatory Assets, Noncurrent	$ 3,826	4,286	4,439
Other Regulatory Assets
Regulatory Assets [Line Items]
Regulatory Assets, Current	14,613	7,539	13,316
Regulatory Assets, Noncurrent	$ 6,840	$ 7,397	$ 8,660
Minimum [Member] | Natural gas costs recoverable through rate adjustments
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	Up to 1 year
Minimum [Member] | Cost recovery mechanisms
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	Up to 1 year
Minimum [Member] | Other Regulatory Assets
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	Up to 1 year
Maximum [Member] | Natural gas costs recoverable through rate adjustments
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	Up to 3 years
Maximum [Member] | Cost recovery mechanisms
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	Up to 10 years
Maximum [Member] | Other Regulatory Assets
Regulatory Assets [Line Items]
Estimated Recovery Period as of September 30, 2020	Up to 19 years

Regulatory assets and liabili_4

Regulatory assets and liabilities Regulatory Liabilities (Details 2) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	$ 39,837	$ 42,935	$ 36,945
Regulatory Liability, Noncurrent	434,936	447,370	453,760
Total regulatory liabilities	474,773	490,305	490,705
Net regulatory position	(25,884)	(72,908)	(58,725)
Natural gas costs refundable through rate adjustments
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	20,556	23,825	19,194
Electric fuel and purchased power deferral
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	6,171	5,824	2,040
Taxes refundable to customers
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	4,223	3,472	4,309
Regulatory Liability, Noncurrent	232,186	246,034	253,703
Plant removal and decommissioning costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Noncurrent	173,367	173,722	174,595
Pension and postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liability, Noncurrent	17,991	18,065	15,190
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	8,887	9,814	11,402
Regulatory Liability, Noncurrent	$ 11,392	$ 9,549	$ 10,272

Fair value measurements Insuran

Fair value measurements Insurance contracts (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Investments used to satisfy nonqualified benefit plans obligations	$ 95.7	$ 84.2	$ 95.7	$ 84.2	$ 87
Net unrealized gain on investments used to satisfy obligations under nonqualified benefit plans	$ 3.3	$ 1.1	$ 8.7	$ 10.4

Available-for-sale securities (

Available-for-sale securities (Details 2) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Available-for-sale securities [Abstract]
Cost	$ 10,979	$ 11,032	$ 10,835
Gross Unrealized Gains	216	88	86
Gross Unrealized Losses	4	10	17
Fair Value	11,191	11,110	10,904
Mortgage-backed securities
Available-for-sale securities [Abstract]
Cost	9,813	9,804	9,577
Gross Unrealized Gains	213	87	86
Gross Unrealized Losses	4	10	16
Fair Value	10,022	9,881	9,647
U.S. Treasury securities
Available-for-sale securities [Abstract]
Cost	1,166	1,228	1,258
Gross Unrealized Gains	3	1	0
Gross Unrealized Losses	0	0	1
Fair Value	$ 1,169	$ 1,229	$ 1,257

Fair value measurements (Detail

Fair value measurements (Details 3) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Concentration risks, percentage [Abstract]
Percentage in fixed-income and other investments	68.00%	51.00%	53.00%
Percentage investment in common stock of large-cap companies	15.00%	23.00%	21.00%
Percentage investment in common stock of mid-cap companies	6.00%	12.00%	11.00%
Percentage investment in common stock of small-cap companies	6.00%	10.00%	10.00%
Percentage investment in target date investments	4.00%	3.00%	3.00%
Percentage investment in cash and cash equivalents	1.00%	1.00%	2.00%
Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 115,356	$ 106,559	$ 102,598
Fair value, measurements, recurring | Money market funds
Fair value measurements [Line Items]
Assets, fair value disclosure	8,478	8,440	7,472
Fair value, measurements, recurring | Insurance contract*
Fair value measurements [Line Items]
Assets, fair value disclosure	95,687	87,009	84,222
Fair value, measurements, recurring | Mortgage-backed securities
Fair value measurements [Line Items]
Assets, fair value disclosure	10,022	9,881	9,647
Fair value, measurements, recurring | U.S. Treasury securities
Fair value measurements [Line Items]
Assets, fair value disclosure	1,169	1,229	1,257
Fair value, measurements, recurring | Fair value, inputs, level 2
Fair value measurements [Line Items]
Assets, fair value disclosure	115,356	106,559	102,598
Fair value, measurements, recurring | Fair value, inputs, level 2 | Money market funds
Fair value measurements [Line Items]
Assets, fair value disclosure	8,478	8,440	7,472
Fair value, measurements, recurring | Fair value, inputs, level 2 | Insurance contract*
Fair value measurements [Line Items]
Assets, fair value disclosure	95,687	87,009	84,222
Fair value, measurements, recurring | Fair value, inputs, level 2 | Mortgage-backed securities
Fair value measurements [Line Items]
Assets, fair value disclosure	10,022	9,881	9,647
Fair value, measurements, recurring | Fair value, inputs, level 2 | U.S. Treasury securities
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 1,169	$ 1,229	$ 1,257

Fair value measurements (Deta_2

Fair value measurements (Details 4)	3 Months Ended
	Sep. 30, 2019USD ($)
Fair Value Disclosures [Abstract]
Investments, Fair Value Disclosure	$ 0
Asset Impairment Charges	$ 2,000,000

Fair value measurements (Deta_3

Fair value measurements (Details 5) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Fair value, balance sheet grouping [Line Items]
Long-term debt	$ 2,270,290	$ 2,243,107	$ 2,246,756
Carrying amount
Fair value, balance sheet grouping [Line Items]
Long-term debt	2,270,290	2,243,107	2,246,756
Fair value
Fair value, balance sheet grouping [Line Items]
Long-term debt, fair value	$ 2,593,743	$ 2,418,631	$ 2,450,209

Long-term debt outstanding (Det

Long-term debt outstanding (Details 1) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Long-term debt outstanding [Line Items]
Long-term debt	$ 2,270,290	$ 2,243,107	$ 2,246,756
Long-term debt due within one year	1,558	16,540	65,810
Long-term debt	$ 2,268,732	2,226,567	2,180,946
Senior Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	4.43%
Long-term debt	$ 1,900,000	1,850,000	1,655,000
Commercial Paper
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	0.44%
Long-term debt	$ 214,150	222,900	281,800
Term Loan Agreements
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	2.00%
Long-term debt	$ 8,400	9,100	209,100
Credit Agreements
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	2.40%
Long-term debt	$ 91,000	89,050	31,000
Medium-term Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	7.32%
Long-term debt	$ 35,000	50,000	50,000
Other Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	4.60%
Long-term debt	$ 28,284	29,117	26,083
Long-term Debt
Long-term debt outstanding [Line Items]
Unamortized Debt Issuance Costs	6,526	7,010	6,074
Discount	$ 18	$ 50	$ 153

Schedule of debt maturities (De

Schedule of debt maturities (Details 2) $ in Thousands	Sep. 30, 2020USD ($)
Long-term debt maturities [Line Items]
Remainder of 2020	$ 28
2021	1,528
2022	148,038
2023	77,921
2024	366,571
Thereafter	$ 1,682,748

Cash flow information (Details)

Cash flow information (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Interest, net*	$ 63,086	$ 64,596
Income taxes paid, net**	43,448	1,816
AFUDC borrowed	2,000	2,000
Right-of-use assets obtained in exchange for new operating lease liabilities	41,315	46,770	$ 54,880
Property, plant and equipment additions in accounts payable	33,240	34,368	46,119
Accrual for holdback payment related to a business combination	5,000	0	0
Debt assumed in connection with a business combination	0	1,163	$ 1,163
Continuing and discontinued operations
Income taxes paid, net**	$ 43,500	$ 2,000

Business segment data (Details)

Business segment data (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 1,587,289			$ 1,563,799			$ 4,147,591	$ 3,958,563
Operating income (loss)	203,711			189,470			399,036	351,000
Income from continuing operations	153,015			136,128			278,395	240,362
Income (loss) from discontinued operations, net of tax	63			1,509			(484)	26
Net income	153,078	$ 99,703	$ 25,130	137,637	$ 61,825	$ 40,926	277,911	240,388
Electric
Segment Reporting Information [Line Items]
Revenues	87,447			89,845			249,793	263,423
Operating income (loss)	21,159			21,930			48,827	49,708
Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	94,703			93,642			562,641	569,656
Operating income (loss)	(18,393)			(15,565)			32,285	32,132
Pipeline
Segment Reporting Information [Line Items]
Revenues	32,068			32,533			70,381	69,827
Operating income (loss)	11,762			11,416			35,406	32,017
Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	822,439			869,376			1,705,629	1,692,287
Operating income (loss)	148,522			143,024			179,994	147,622
Construction services
Segment Reporting Information [Line Items]
Revenues	550,608			478,381			1,559,217	1,363,305
Operating income (loss)	40,507			29,950			102,185	89,381
Other
Segment Reporting Information [Line Items]
Revenues	24			22			(70)	65
Operating income (loss)	154			(1,285)			339	140
Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(7,543)			(8,043)			(50,849)	(51,328)
Intersegment eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	(195)			0			(586)	0
Intersegment eliminations | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	(185)			0			(555)	0
Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	(3,622)			(3,831)			(36,820)	(35,298)
Intersegment eliminations | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	(110)			(124)			(262)	(388)
Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	(425)			(1,226)			(3,674)	(2,076)
Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	(3,006)			(2,862)			(8,952)	(13,566)
Total intersegment operating revenues
Segment Reporting Information [Line Items]
Revenues	0			0			0	0
Regulated operation
Segment Reporting Information [Line Items]
Revenues	210,115			209,444			870,151	885,309
Income from continuing operations	6,985			7,599			77,991	74,206
Regulated operation | Electric
Segment Reporting Information [Line Items]
Revenues	87,447			89,845			249,793	263,423
Income from continuing operations	16,787			16,291			40,314	39,267
Regulated operation | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	94,703			93,642			562,641	569,656
Income from continuing operations	(17,614)			(15,625)			13,795	14,623
Regulated operation | Pipeline
Segment Reporting Information [Line Items]
Revenues	27,965			25,957			57,717	52,230
Income from continuing operations	7,812			6,933			23,882	20,316
Regulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	3,923			3,750			37,724	35,098
Regulated operation | Intersegment eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	195			0			586	0
Regulated operation | Intersegment eliminations | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	185			0			555	0
Regulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	3,543			3,750			36,583	35,098
Nonregulated operation
Segment Reporting Information [Line Items]
Revenues	1,377,174			1,354,355			3,277,440	3,073,254
Income from continuing operations	146,030			128,529			200,404	166,156
Nonregulated operation | Pipeline
Segment Reporting Information [Line Items]
Revenues	4,103			6,576			12,664	17,597
Income from continuing operations	189			801			444	1,380
Nonregulated operation | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	822,439			869,376			1,705,629	1,692,287
Income from continuing operations	107,307			102,611			122,113	97,328
Nonregulated operation | Construction services
Segment Reporting Information [Line Items]
Revenues	550,608			478,381			1,559,217	1,363,305
Income from continuing operations	29,789			21,113			74,544	63,982
Nonregulated operation | Other
Segment Reporting Information [Line Items]
Revenues	24			22			(70)	65
Income from continuing operations	8,745			4,004			3,303	3,466
Nonregulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	3,620			4,293			13,125	16,230
Nonregulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	79			81			237	200
Nonregulated operation | Intersegment eliminations | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	110			124			262	388
Nonregulated operation | Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	425			1,226			3,674	2,076
Nonregulated operation | Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	$ 3,006			$ 2,862			$ 8,952	$ 13,566

Employee benefit plans (Details

Employee benefit plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Qualified plan | Underfunded plan | Pension benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	3,023	3,806	9,070	11,419
Expected return on assets	(4,987)	(4,559)	(14,962)	(13,677)
Amortization of prior service credit	0	0	0	0
Amortization of net actuarial loss	1,793	1,387	5,379	4,160
Net periodic benefit cost (credit), including amount capitalized	(171)	634	(513)	1,902
Less amount capitalized	0	0	0	0
Net periodic benefit cost (credit)	(171)	634	(513)	1,902
Qualified plan | Overfunded Plan | Other postretirement benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	383	286	1,149	857
Interest cost	609	746	1,827	2,239
Expected return on assets	(1,115)	(1,201)	(3,764)	(3,603)
Amortization of prior service credit	(349)	(289)	(1,048)	(866)
Amortization of net actuarial loss	71	27	215	82
Net periodic benefit cost (credit), including amount capitalized	(401)	(431)	(1,621)	(1,291)
Less amount capitalized	39	26	106	84
Net periodic benefit cost (credit)	(440)	(457)	(1,727)	(1,375)
Nonqualified plan | Unfunded plan | Supplemental employee retirement plans
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Net periodic benefit cost (credit)	$ 1,000	$ 1,100	$ 2,900	$ 3,300

MNPUC (Details)

MNPUC (Details) - MNPUC [Member] - Gas Distribution [Member] - Great Plains Natural Gas Co. [Member] - USD ($) $ in Millions	Oct. 26, 2020	Jan. 01, 2020	Sep. 27, 2019
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 2.9
Public Utilities, Requested Rate Increase (Decrease), Percentage			12.00%
Public Utilities, Interim Rate Increase (Decrease), Amount		$ 2.6
Public Utilities, Interim Rate Increase (Decrease), Percentage		11.00%
Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 2.6
Public Utilities, Approved Rate Increase (Decrease), Percentage	11.50%

MTPSC (Details 2)

MTPSC (Details 2) - Pending Rate Case [Member] - Gas Distribution [Member] - MTPSC [Member] - Montana-Dakota Utilities Co. [Member] - USD ($) $ in Millions	Feb. 01, 2021	Jun. 22, 2020
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 8.6
Public Utilities, Requested Rate Increase (Decrease), Percentage		13.40%
Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Interim Rate Increase (Decrease), Amount	$ 4.9
Public Utilities, Interim Rate Increase (Decrease), Percentage	8.20%

NDPSC (Details 3)

NDPSC (Details 3) - NDPSC [Member] - Montana-Dakota Utilities Co. [Member] - USD ($) $ in Millions	Jan. 01, 2021	Nov. 01, 2020	Aug. 26, 2020
Electric | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Total Transmission Cost Adjustment Rider		$ 15.5
Transmission Capital Projects Increase (Decrease)		3.3
Public Utilities, Approved Rate Increase (Decrease), Amount		6.3
COVID-19 [Member] | Electric | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Under-Recovered Balance, Transmission Cost Adjustment Rider		$ 1.6
Pending Rate Case [Member] | Gas Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 9
Public Utilities, Requested Rate Increase (Decrease), Percentage			7.80%
Pending Rate Case [Member] | Gas Distribution [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Interim Rate Increase (Decrease), Amount	$ 6.9
Public Utilities, Interim Rate Increase (Decrease), Percentage	6.00%

OPUC (Details 4)

OPUC (Details 4) - OPUC - Pending Rate Case [Member] - Gas Distribution [Member] - Cascade Natural Gas [Member] - USD ($)	Feb. 01, 2021	Mar. 31, 2020
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 4,900,000
Public Utilities, Requested Rate Increase (Decrease), Percentage		7.20%
Environmental Remediation Deferred Costs Increase (Decrease) Amount		$ 364,000
Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 3,200,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage	4.80%

WUTC (Details 5)

WUTC (Details 5) - WUTC [Member] - Cascade Natural Gas [Member] - USD ($) $ in Millions	Nov. 01, 2020	Jun. 19, 2020	May 29, 2020
Pipeline Cost Recovery Mechanism [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 1
Public Utilities, Requested Rate Increase (Decrease), Percentage			0.40%
Pipeline Cost Recovery Mechanism [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 1.1
Public Utilities, Approved Rate Increase (Decrease), Percentage	0.50%
Pending Rate Case [Member] | Gas Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 13.8
Public Utilities, Requested Rate Increase (Decrease), Percentage		5.30%

FERC (Details 6)

FERC (Details 6) $ in Millions	Jan. 01, 2021USD ($)
MISO [Member] | Montana-Dakota Utilities Co. [Member] | Electric | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Transmission Formula Revenue Requirement	$ 12.9

Litigation (Details)

Litigation (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Loss Contingencies [Line Items]
Potential liabilities related to litigation and environmental matters	$ 72.7	$ 29.1	$ 30.6
Insurance Receivable	49.1	16.2	15.3
Regulatory Assets	$ 20.9	$ 10.5	$ 12

Environmental matters (Details

Environmental matters (Details 2) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2020USD ($)
Site Contingency [Line Items]
Total Estimated Costs For Site Remedial Investigation And Feasibility Study		$ 7.6
Incurred Costs For Site Remedial Investigation And Feasibility Study		5.4
Environmental Matters Accrual For Site Remediation, Period Increase	$ 11.1
Environmental Matters Accrual For Remedial Investigation and Feasibility Study Costs	2.2	2.2
Environmental Matters Accrual For Site Remediation	$ 17.5	17.5
Minimum [Member]
Site Contingency [Line Items]
Site Contingency, Loss Exposure Not Accrued, Best Estimate		13.6
Maximum [Member]
Site Contingency [Line Items]
Site Contingency, Loss Exposure Not Accrued, Best Estimate		$ 71

Guarantees (Details 3)

Guarantees (Details 3)	Sep. 30, 2020USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 255,500,000
Fixed maximum amounts guaranteed by year 2020	23,800,000
Fixed maximum amounts guaranteed by year 2021	199,700,000
Fixed maximum amounts guaranteed by year 2022	16,100,000
Fixed maximum amounts guaranteed by year 2023	5,300,000
Fixed maximum amounts guaranteed by year 2024	500,000
Fixed maximum amounts guaranteed, thereafter	1,100,000
No scheduled maturity date	9,000,000
Amount outstanding under guarantees that is reflected on balance sheet	0
Letters of credit	22,500,000
Letters of credit set to expire - 2020	20,200,000
Letters of credit set to expire - 2021	1,800,000
Letters of credit set to expire - 2022	500,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	$ 922,700,000

Variable interest entities (Det

Variable interest entities (Details 4) $ in Millions	Sep. 30, 2020USD ($)
Fuel contract
Variable Interest Entities [Line Items]
Variable interest entity, reporting entity involvement, maximum loss exposure, amount	$ 34.2