MDU Resources (MDU) 10-Q 1 Nov 19 2019 Q3 Quarterly report Financial data

Cover page

Cover page - shares	9 Months Ended
	Sep. 30, 2019	Oct. 25, 2019
Entity Information [Line Items]
Document type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
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		200,383,869
Entity Central Index Key	0000067716
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating revenues:
Operating revenues:	$ 1,563,799	$ 1,280,787	$ 3,958,563	$ 3,321,678
Operating expenses:
Operation and maintenance:	1,212,620	996,591	2,936,564	2,419,531
Purchased natural gas sold	31,843	32,123	270,539	270,319
Depreciation, depletion and amortization	65,021	55,016	187,937	161,298
Taxes, other than income	46,128	38,647	148,110	128,257
Electric fuel and purchased power	18,717	18,406	64,413	58,901
Total operating expenses	1,374,329	1,140,783	3,607,563	3,038,306
Operating income	189,470	140,004	351,000	283,372
Other income	3,014	2,683	12,222	4,864
Interest expense	25,258	20,955	74,094	62,202
Income before income taxes	167,226	121,732	289,128	226,034
Income taxes	31,098	14,363	48,766	32,629
Income from continuing operations	136,128	107,369	240,362	193,405
Income (loss) from discontinued operations, net of tax (Note 10)	1,509	(118)	26	85
Net income	$ 137,637	$ 107,251	$ 240,388	$ 193,490
Earnings per share - basic:
Income from continuing operations	$ 0.68	$ 0.55	$ 1.21	$ 0.99
Discontinued operations, net of tax	0.01	0	0	0
Earnings per share - basic	0.69	0.55	1.21	0.99
Earnings per share - diluted:
Income from continuing operations	0.68	0.55	1.21	0.99
Discontinued operations, net of tax	0.01	0	0	0
Earnings per share - diluted	$ 0.69	$ 0.55	$ 1.21	$ 0.99
Weighted average common shares outstanding - basic	199,343	196,018	198,016	195,618
Weighted average common shares outstanding - diluted	199,383	196,265	198,033	196,104
Regulated operation
Operating revenues:
Operating revenues:	$ 209,444	$ 200,617	$ 885,309	$ 851,761
Operating expenses:
Operation and maintenance:	86,249	82,920	262,434	252,961
Income from continuing operations	7,599	13,506	74,206	72,193
Nonregulated operation
Operating revenues:
Operating revenues:	1,354,355	1,080,170	3,073,254	2,469,917
Operating expenses:
Operation and maintenance:	1,126,371	913,671	2,674,130	2,166,570
Income from continuing operations	$ 128,529	$ 93,863	$ 166,156	$ 121,212

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net income	$ 137,637	$ 107,251	$ 240,388	$ 193,490
Other comprehensive income:
Reclassification adjustment for loss on derivative instruments included in net income, net of tax of $36 and $55 for the three months ended and $(177) and $164 for the nine months ended in 2019 and 2018, respectively	112	92	620	279
Postretirement liability adjustment:
Amortization of postretirement liability losses included in net periodic benefit cost, net of tax of $95 and $142 for the three months ended and $284 and $442 for the nine months ended in 2019 and 2018, respectively	292	442	878	1,309
Foreign currency translation adjustment:
Foreign currency translation adjustment recognized during the period, net of tax of $0 and $0 for the three months ended and $0 and $(14) for the nine months ended in 2019 and 2018, respectively	0	0	0	(61)
Reclassification adjustment for foreign currency translation adjustment included in net income, net of tax of $0 and $0 for the three months ended and $0 and $75 for the nine months ended in 2019 and 2018, respectively	0	0	0	249
Foreign currency translation adjustment	0	0	0	188
Net unrealized gain (loss) on available-for-sale investments:
Net unrealized gain (loss) on available-for-sale investments arising during the period, net of tax of $3 and $(13) for the three months ended and $35 and $(52) for the nine months ended in 2019 and 2018, respectively	12	(51)	130	(199)
Reclassification adjustment for (gain) loss on available-for-sale investments included in net income, net of tax of $(1) and $9 for the three months ended and $10 and $26 for the nine months ended in 2019 and 2018, respectively	(4)	33	36	97
Net unrealized gain (loss) on available-for-sale investments	8	(18)	166	(102)
Other comprehensive income	412	516	1,664	1,674
Comprehensive income attributable to common stockholders	$ 138,049	$ 107,767	$ 242,052	$ 195,164

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income - Parenthetical - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification adjustment for loss on derivative instruments included in net income, tax	$ 36	$ 55	$ (177)	$ 164
Amortization of postretirement liability losses included in net periodic benefit cost, tax	95	142	284	442
Foreign currency translation adjustments recognized during the period, tax	0	0	0	(14)
Reclassification of foreign currency translation adjustment	0	0	0	75
Net unrealized gain (loss) on available-for-sale investments arising during the period, tax	3	(13)	35	(52)
Reclassification adjustment for (gain) loss on available-for-sale investments included in net income, tax	$ (1)	$ 9	$ 10	$ 26

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Current assets:
Cash and cash equivalents	$ 67,000	$ 53,948	$ 67,077
Receivables, net	968,279	722,945	787,344
Inventories	286,057	287,309	270,293
Prepayments and other current assets	140,053	119,500	88,760
Current assets held for sale	426	430	571
Total current assets	1,461,815	1,184,132	1,214,045
Investments	144,417	138,620	143,303
Property, plant and equipment	7,746,754	7,397,321	7,102,960
Less accumulated depreciation, depletion and amortization	2,944,928	2,818,644	2,796,649
Net property, plant and equipment	4,801,826	4,578,677	4,306,311
Deferred charges and other assets:
Goodwill	681,349	664,922	640,203
Other intangible assets, net	15,511	10,815	4,318
Operating lease right-of-use assets (Note 11)	118,764
Other	504,842	408,857	408,178
Noncurrent assets held for sale	2,087	2,087	1,835
Total deferred charges and other assets	1,322,553	1,086,681	1,054,534
Total assets	7,730,611	6,988,110	6,718,193
Current liabilities:
Short-term borrowings	139,988	0	0
Long-term debt due within one year	65,810	251,854	3,915
Accounts payable	378,370	358,505	339,713
Taxes payable	53,505	41,929	50,461
Dividends payable	40,460	39,695	38,714
Accrued compensation	93,642	69,007	62,836
Current operating lease liabilities (Note 11)	32,584
Other accrued liabilities	225,925	221,059	221,620
Current liabilities held for sale	3,393	4,001	7,959
Total current liabilities	1,033,677	986,050	725,218
Long-term debt	2,180,946	1,856,841	1,911,555
Deferred credits and other liabilities:
Deferred income taxes	487,194	430,085	405,761
Noncurrent operating lease liabilities (Note 11)	86,166
Other	1,147,022	1,148,359	1,154,366
Total deferred credits and other liabilities	1,720,382	1,578,444	1,560,127
Commitments and contingencies
Stockholders' equity:
Authorized - 500,000,000 shares, $1.00 par value Shares issued - 200,876,334 at September 30, 2019, 196,557,245 at September 30, 2018 and 196,564,907 at December 31, 2018	200,876	196,565	196,557
Other paid-in capital	1,351,990	1,248,576	1,247,151
Retained earnings	1,283,044	1,163,602	1,124,830
Accumulated other comprehensive loss	(36,678)	(38,342)	(43,619)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)	(3,626)
Total stockholders' equity	2,795,606	2,566,775	2,521,293
Total liabilities and stockholders' equity	$ 7,730,611	$ 6,988,110	$ 6,718,193

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Stockholders' equity:
Common stock, shares issued	200,876,334	196,564,907	196,557,245
Treasury shares	538,921	538,921	538,921
Common stock, shares authorized	500,000,000	500,000,000	500,000,000
Common stock, par value	$ 1	$ 1	$ 1

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
Cumulative effect of adoption of ASU 2014-09 | Accounting Standards Update 2014-09	$ (970)			$ (970)
Balance (in shares) at Dec. 31, 2017		195,843,297
Treasury stock (in shares) at Dec. 31, 2017						(538,921)
Balance at Dec. 31, 2017	2,429,043	$ 195,843	$ 1,233,412	1,040,748	$ (37,334)	$ (3,626)
Balance (Accounting Standards Update 2014-09) at Dec. 31, 2017	2,428,073			1,039,778
Net income	42,437			42,437
Other comprehensive income	433				433
Reclassification of certain prior period tax effects from accumulated other comprehensive loss | Adjustments for new accounting pronouncement	0			7,959	(7,959)
Dividends declared on common stock	(38,705)			(38,705)
Stock-based compensation	1,223		1,223
Repurchase of common stock						(182,424)
Repurchase of common stock	(5,020)					$ (5,020)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings			(7,350)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)						182,424
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings						$ 5,020
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(2,330)
Balance (in shares) at Mar. 31, 2018		195,843,297
Treasury stock (in shares) at Mar. 31, 2018						(538,921)
Balance at Mar. 31, 2018	2,426,111	$ 195,843	1,227,285	1,051,469	(44,860)	$ (3,626)
Balance (in shares) at Dec. 31, 2017		195,843,297
Treasury stock (in shares) at Dec. 31, 2017						(538,921)
Balance at Dec. 31, 2017	2,429,043	$ 195,843	1,233,412	1,040,748	(37,334)	$ (3,626)
Balance (Accounting Standards Update 2014-09) at Dec. 31, 2017	2,428,073			1,039,778
Net income	193,490
Other comprehensive income	1,674
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	$ (2,330)
Balance (in shares) at Sep. 30, 2018	196,557,245	196,557,245
Treasury stock (in shares) at Sep. 30, 2018						(538,921)
Balance at Sep. 30, 2018	$ 2,521,293	$ 196,557	1,247,151	1,124,830	(43,619)	$ (3,626)
Balance (in shares) at Mar. 31, 2018		195,843,297
Treasury stock (in shares) at Mar. 31, 2018						(538,921)
Balance at Mar. 31, 2018	2,426,111	$ 195,843	1,227,285	1,051,469	(44,860)	$ (3,626)
Net income	43,802			43,802
Other comprehensive income	725				725
Dividends declared on common stock	(38,847)			(38,847)
Stock-based compensation	1,294		1,294
Issuance of common stock (shares)		713,948
Issuance of common stock	17,993	$ 714	17,279
Balance (in shares) at Jun. 30, 2018		196,557,245
Treasury stock (in shares) at Jun. 30, 2018						(538,921)
Balance at Jun. 30, 2018	2,451,078	$ 196,557	1,245,858	1,056,424	(44,135)	$ (3,626)
Net income	107,251			107,251
Other comprehensive income	516				516
Dividends declared on common stock	(38,845)			(38,845)
Stock-based compensation	$ 1,293		1,293
Balance (in shares) at Sep. 30, 2018	196,557,245	196,557,245
Treasury stock (in shares) at Sep. 30, 2018						(538,921)
Balance at Sep. 30, 2018	$ 2,521,293	$ 196,557	1,247,151	1,124,830	(43,619)	$ (3,626)
Balance (in shares) at Dec. 31, 2018	196,564,907	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
Share Based Compensation, Shares, Shares Issued Net Of Tax Withholdings		246,214
Share Based Compensation Value Issued Shares Net Of Tax Withholdings		$ 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
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)
Balance (in shares) at Dec. 31, 2018	196,564,907	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)
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)
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
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
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)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities:
Net income	$ 240,388	$ 193,490
Income (loss) from discontinued operations, net of tax	26	85
Income from continuing operations	240,362	193,405
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	187,937	161,298
Deferred income taxes	49,222	42,428
Changes in current assets and liabilities, net of acquisitions:
Receivables	(238,373)	(55,749)
Inventories	2,480	(38,785)
Other current assets	(69,105)	(3,452)
Accounts payable	13,062	16,155
Other current liabilities	53,458	31,971
Other noncurrent changes	(35,361)	(27,170)
Net cash provided by continuing operations	203,682	320,101
Net cash used in discontinued operations	(579)	(2,720)
Net cash provided by operating activities	203,103	317,381
Investing activities:
Capital expenditures	(423,036)	(345,599)
Acquisitions, net of cash acquired	(53,263)	(27,858)
Net proceeds from sale or disposition of property and other	28,391	12,451
Investments	(717)	(1,560)
Net cash used in continuing operations	(448,625)	(362,566)
Net cash provided by discontinued operations	0	1,236
Net cash used in investing activities	(448,625)	(361,330)
Financing activities:
Issuance of short-term borrowings	169,977	0
Repayment of short-term borrowings	(30,000)	0
Issuance of long-term debt	302,724	356,952
Repayment of long-term debt	(166,956)	(157,315)
Proceeds from issuance of common stock	105,639	0
Dividends paid	(119,795)	(115,859)
Repurchase of common stock	0	(5,020)
Tax withholding on stock-based compensation	(3,015)	(2,330)
Net cash provided by financing activities	258,574	76,428
Effect of exchange rate changes on cash and cash equivalents	0	(1)
Increase in cash and cash equivalents	13,052	32,478
Cash and cash equivalents -- beginning of year	53,948	34,599
Cash and cash equivalents -- end of period	$ 67,000	$ 67,077

Basis of presentation

Basis of presentation	9 Months Ended
	Sep. 30, 2019
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 2018 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. On January 2, 2019, the Company announced the completion of the Holding Company Reorganization, which resulted in Montana-Dakota becoming a subsidiary of the Company. The purpose of the reorganization was to make the public utility division into a subsidiary of the holding company, just as the other operating companies are wholly owned subsidiaries. Effective January 1, 2019, the Company adopted the requirements of the ASU on leases, as further discussed in Notes 6 and 11 . As such, results for reporting periods beginning January 1, 2019, are presented under the new guidance, while prior period amounts are not adjusted and continue to be reported in accordance with the historic accounting for leases. The assets and liabilities for the Company's discontinued operations have been classified as held for sale and the results of operations are shown in income (loss) from discontinued operations, other than certain general and administrative costs and interest expense which do not meet the criteria for income (loss) from discontinued operations. At the time the assets were classified as held for sale, depreciation, depletion and amortization expense was no longer recorded. Unless otherwise indicated, the amounts presented in the accompanying notes to the consolidated financial statements relate to the Company's continuing operations. For more information on the Company's discontinued operations, see Note 10 . Management has also evaluated the impact of events occurring after September 30, 2019 , up to the date of issuance of these consolidated interim financial statements.

Seasonality of operations

Seasonality of operations	9 Months Ended
	Sep. 30, 2019
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.

Accounts receivable and allowan

Accounts receivable and allowance for doubtful accounts	9 Months Ended
	Sep. 30, 2019
Receivables [Abstract]
Accounts receivable and allowance for doubtful accounts	Accounts receivable and allowance for doubtful accounts Accounts receivable consists primarily of trade receivables from the sale of goods and services which are recorded at the invoiced amount net of allowance for doubtful accounts, and costs and estimated earnings in excess of billings on uncompleted contracts. The total balance of receivables past due 90 days or more was $56.0 million , $29.2 million and $30.0 million at September 30, 2019 and 2018 , and December 31, 2018 , respectively. The allowance for doubtful accounts is determined through a review of past due balances and other specific account data. Account balances are written off when management determines the amounts to be uncollectible. The Company's allowance for doubtful accounts at September 30, 2019 and 2018 , and December 31, 2018 , was $8.7 million , $7.3 million and $8.9 million , respectively.

Inventories and natural gas in

Inventories and natural gas in storage	9 Months Ended
	Sep. 30, 2019
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 carried at lower of cost or net realizable value, or cost using the last-in, first-out method. All other inventories are stated at the lower of cost or net realizable value. The portion of the cost of natural gas in storage expected to be used within one year was included in inventories. Inventories on the Consolidated Balance Sheets were as follows: September 30, 2019 September 30, 2018 December 31, 2018 (In thousands) Aggregates held for resale $ 143,157 $ 133,477 $ 139,681 Asphalt oil 39,269 40,781 54,741 Materials and supplies 25,696 23,563 23,611 Merchandise for resale 23,902 15,954 22,552 Natural gas in storage (current) 32,164 29,084 22,117 Other 21,869 27,434 24,607 Total $ 286,057 $ 270,293 $ 287,309 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 deferred charges and other assets - other and was $ 48.2 million , $ 47.8 million and $ 48.5 million at September 30, 2019 and 2018 , and December 31, 2018 , respectively.

Earnings per common share

Earnings per common share	9 Months Ended
	Sep. 30, 2019
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, 2019 2018 2019 2018 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 199,343 196,018 198,016 195,618 Effect of dilutive performance share awards and restricted stock units 40 247 17 486 Weighted average common shares outstanding - diluted 199,383 196,265 198,033 196,104 Shares excluded from the calculation of diluted earnings per share 155 114 243 — Dividends declared per common share $ .2025 $ .1975 $ .6075 $ .5925

New accounting standards

New accounting standards	9 Months Ended
	Sep. 30, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New accounting standards	New accounting standards Recently adopted accounting standards ASU 2016-02 - Leases In February 2016, the FASB issued guidance regarding leases. The guidance required lessees to recognize a lease liability and a right-of-use asset on the balance sheet for operating and financing leases. The guidance remained largely the same for lessors, although some changes were made to better align lessor accounting with the new lessee accounting and to align with the revenue recognition standard. The guidance also required additional disclosures, both quantitative and qualitative, related to operating and financing leases for the lessee and sales-type, direct financing and operating leases for the lessor. The Company adopted the standard on January 1, 2019. In July 2018, the FASB issued ASU 2018-11 - Leases: Targeted Improvements , an accounting standard update to ASU 2016-02. This ASU provided an entity the option to adopt the guidance using one of two modified retrospective approaches. An entity could adopt the guidance using the modified retrospective transition approach beginning in the earliest year presented in the financial statements. This method of adoption would have required the restatement of prior periods reported and the presentation of lease disclosures under the new guidance for all periods reported. The additional transition method of adoption, introduced by ASU 2018-11, allowed entities the option to apply the guidance on the date of adoption by recognizing a cumulative effect adjustment to retained earnings during the period of adoption and did not require prior comparative periods to be restated. The Company adopted the standard on January 1, 2019, utilizing the additional transition method of adoption applied on the date of adoption and the practical expedient that allowed the Company to not reassess whether an expired or existing contract contained a lease, the classification of leases or initial direct costs. The Company did not identify any cumulative effect adjustments. The Company also adopted a short-term leasing policy as the lessee where leases with a term of 12 months or less are not included on the Consolidated Balance Sheet. As a practical expedient, a lessee may choose not to separate nonlease components from lease components and instead account for lease and nonlease components as a single lease component. The election shall be made by asset class. The Company has elected to adopt the lease/nonlease component practical expedient for all asset classes as the lessee. The Company did not elect the practical expedient to use hindsight when assessing the lease term or impairment of right-of-use assets for the existing leases on the date of adoption. In January 2018, the FASB issued a practical expedient for land easements under the new lease guidance. The practical expedient permits an entity to elect the option to not evaluate land easements under the new guidance if they existed or expired before the adoption of the new lease guidance and were not previously accounted for as leases under the previous lease guidance. Once an entity adopts the new guidance, the entity should apply the new guidance on a prospective basis to all new or modified land easements. The Company has adopted this practical expedient. The Company formed a lease implementation team to review and assess existing contracts to identify and evaluate those containing leases. Additionally, the team implemented new and revised existing software to meet the reporting and disclosure requirements of the standard. The Company also assessed the impact the standard had on its processes and internal controls and identified new and updated existing internal controls and processes to ensure compliance with the new lease standard; such modifications were not deemed to be significant. During the assessment phase, the Company used various surveys, reconciliations and analytic methodologies to ensure the completeness of the lease inventory. The Company determined that most of the current operating leases were subject to the guidance and were recognized as operating lease liabilities and right-of-use assets on the Consolidated Balance Sheet upon adoption. On January 1, 2019, the Company recorded approximately $112 million to right-of-use assets and lease liabilities as a result of the initial adoption of the guidance. In addition, the Company evaluated the impact the new guidance had on lease contracts where the Company is the lessor and determined it did not have a significant impact to the Company's financial statements. ASU 2018-15 - Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract In August 2018, the FASB issued guidance on the accounting for implementation costs of a hosting arrangement that is a service contract. The guidance aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract similar to the costs incurred to develop or obtain internal-use software and such capitalized costs to be expensed over the term of the hosting arrangement. Costs incurred during the preliminary and postimplementation stages should continue to be expensed as activities are performed. The capitalized costs are required to be presented on the balance sheet in the same line the prepayment for the fees associated with the hosting arrangement would be presented. In addition, the expense related to the capitalized implementation costs should be presented in the same line on the income statement as the fees associated with the hosting element of the arrangements. The Company adopted the guidance effective January 1, 2019, on a prospective basis. The adoption of the guidance did not have a material impact on its results of operations, financial position, cash flows or disclosures. Recently issued accounting standards not yet adopted ASU 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 introduces a new impairment model known as the current expected credit loss model that will replace the incurred loss impairment methodology currently included under GAAP. This guidance requires 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 guidance will be effective for the Company on January 1, 2020, and must be applied on a modified retrospective basis with early adoption permitted. The Company continues to evaluate the provisions of the guidance and currently does not expect the guidance to have a material impact on its results of operations, financial position, cash flows or disclosures. ASU 2017-04 - Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued guidance on simplifying the test for goodwill impairment by eliminating Step 2, which required an entity to measure the amount of impairment loss by comparing the implied fair value of reporting unit goodwill with the carrying amount of such goodwill. This guidance requires entities to perform a quantitative impairment test, previously Step 1, to identify both the existence of impairment and the amount of impairment loss by comparing the fair value of a reporting unit to its carrying amount. Entities will continue to have the option of performing a qualitative assessment to determine if the quantitative impairment test is necessary. The guidance also requires additional disclosures if an entity has one or more reporting units with zero or negative carrying amounts of net assets. The guidance will be effective for the Company on January 1, 2020, and must be applied on a prospective basis with early adoption permitted. The Company has evaluated the guidance and does not expect the guidance will have a material impact on its results of operations, financial position, cash flows or disclosures upon adoption. The Company is planning to early adopt the guidance with the preparation of its 2019 goodwill impairment test in the fourth quarter of 2019. 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 modifies, among other things, the disclosures required for Level 3 fair value measurements, including the range and weighted average of significant unobservable inputs. The guidance removes, among other things, the disclosure requirement to disclose transfers between Levels 1 and 2. The guidance will be effective for the Company on January 1, 2020, including interim periods, with early adoption permitted. Level 3 fair value measurement disclosures should be applied prospectively while all other amendments should be applied retrospectively. The Company is evaluating the effects the adoption of the new guidance will have on its disclosures. 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.

Accumulated other comprehensive

Accumulated other comprehensive income (loss)	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Comprehensive income (loss)	Accumulated other comprehensive income (loss) The after-tax changes in the components of accumulated other comprehensive income (loss) were as follows: Nine Months Ended September 30, 2019 Net Unrealized Gain (Loss) on Derivative 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 ) Nine Months Ended September 30, 2018 Net Unrealized Gain (Loss) on Derivative Postretirement Foreign Net Unrealized Total (In thousands) At December 31, 2017 $ (1,934 ) $ (35,163 ) $ (155 ) $ (82 ) $ (37,334 ) Other comprehensive loss before reclassifications — — (2 ) (105 ) (107 ) Amounts reclassified from accumulated other comprehensive loss 92 418 — 30 540 Net current-period other comprehensive income (loss) 92 418 (2 ) (75 ) 433 Reclassification adjustment of prior period tax effects related to TCJA included in accumulated other comprehensive loss (389 ) (7,520 ) (33 ) (17 ) (7,959 ) At March 31, 2018 $ (2,231 ) $ (42,265 ) $ (190 ) $ (174 ) $ (44,860 ) Other comprehensive loss before reclassifications — — (59 ) (43 ) (102 ) Amounts reclassified from accumulated other comprehensive loss 95 449 249 34 827 Net current-period other comprehensive income (loss) 95 449 190 (9 ) 725 At June 30, 2018 $ (2,136 ) $ (41,816 ) $ — $ (183 ) $ (44,135 ) Other comprehensive loss before reclassifications — — — (51 ) (51 ) Amounts reclassified from accumulated other comprehensive loss 92 442 — 33 567 Net current-period other comprehensive income (loss) 92 442 — (18 ) 516 At September 30, 2018 $ (2,044 ) $ (41,374 ) $ — $ (201 ) $ (43,619 ) The following amounts were reclassified out of accumulated other comprehensive loss into net income. The amounts presented in parenthesis indicate a decrease to net income on the Consolidated Statements of Income. The reclassifications were as follows: Three Months Ended Nine Months Ended Location on Consolidated Statements of Income September 30, September 30, 2019 2018 2019 2018 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ (148 ) $ (147 ) $ (443 ) $ (443 ) Interest expense 36 55 (177 ) 164 Income taxes (112 ) (92 ) (620 ) (279 ) Amortization of postretirement liability losses included in net periodic benefit cost (387 ) (584 ) (1,162 ) (1,751 ) Other income 95 142 284 442 Income taxes (292 ) (442 ) (878 ) (1,309 ) Reclassification adjustment for foreign currency translation adjustment included in net income — — — (324 ) Other income — — — 75 Income taxes — — — (249 ) Reclassification adjustment on available-for-sale investments included in net income 5 (42 ) (46 ) (123 ) Other income (1 ) 9 10 26 Income taxes 4 (33 ) (36 ) (97 ) Total reclassifications $ (400 ) $ (567 ) $ (1,534 ) $ (1,934 )

Revenue from contracts with cus

Revenue from contracts with customers	9 Months Ended
	Sep. 30, 2019
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. As part of the adoption of ASC 606 - Revenue from Contracts with Customers , the Company elected the practical expedient to recognize the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that the Company otherwise would have recognized is 12 months or less. Disaggregation In the following table, revenue is disaggregated by the type of customer or service provided. The Company believes this level of disaggregation best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The table also includes a reconciliation of the disaggregated revenue by reportable segments. For more information on the Company's business segments, see Note 17 . Three Months Ended September 30, 2019 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services 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 * Intrasegment revenues are presented 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. Three Months Ended September 30, 2018 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 31,424 $ 43,825 $ — $ — $ — $ — $ 75,249 Commercial utility sales 36,259 28,174 — — — — 64,433 Industrial utility sales 8,738 4,421 — — — — 13,159 Other utility sales 2,056 — — — — — 2,056 Natural gas transportation — 10,841 21,400 — — — 32,241 Natural gas gathering — — 2,320 — — — 2,320 Natural gas storage — — 2,795 — — — 2,795 Contracting services — — — 409,006 — — 409,006 Construction materials — — — 538,962 — — 538,962 Intrasegment eliminations* — — — (204,040 ) — — (204,040 ) Inside specialty contracting — — — — 217,474 — 217,474 Outside specialty contracting — — — — 100,988 — 100,988 Other 6,158 3,208 5,701 — 15 3,084 18,166 Intersegment eliminations — — (3,187 ) (165 ) (782 ) (3,037 ) (7,171 ) Revenues from contracts with customers 84,635 90,469 29,029 743,763 317,695 47 1,265,638 Revenues out of scope 1,445 1,779 42 — 11,883 — 15,149 Total external operating revenues $ 86,080 $ 92,248 $ 29,071 $ 743,763 $ 329,578 $ 47 $ 1,280,787 * Intrasegment revenues are presented 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. Nine Months Ended September 30, 2019 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services 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 * Intrasegment revenues are presented 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. Nine Months Ended September 30, 2018 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 93,359 $ 305,399 $ — $ — $ — $ — $ 398,758 Commercial utility sales 103,636 185,885 — — — — 289,521 Industrial utility sales 25,734 17,457 — — — — 43,191 Other utility sales 5,766 — — — — — 5,766 Natural gas transportation — 32,104 64,505 — — — 96,609 Natural gas gathering — — 6,900 — — — 6,900 Natural gas storage — — 8,563 — — — 8,563 Contracting services — — — 730,628 — — 730,628 Construction materials — — — 1,100,185 — — 1,100,185 Intrasegment eliminations* — — — (363,877 ) — — (363,877 ) Inside specialty contracting — — — — 667,664 — 667,664 Outside specialty contracting — — — — 283,432 — 283,432 Other 22,836 10,821 13,353 — 32 8,536 55,578 Intersegment eliminations — — (31,485 ) (501 ) (1,332 ) (8,343 ) (41,661 ) Revenues from contracts with customers 251,331 551,666 61,836 1,466,435 949,796 193 3,281,257 Revenues out of scope 653 2,786 129 — 36,853 — 40,421 Total external operating revenues $ 251,984 $ 554,452 $ 61,965 $ 1,466,435 $ 986,649 $ 193 $ 3,321,678 * Intrasegment revenues are presented 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, 2019 December 31, 2018 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 163,437 $ 104,239 $ 59,198 Receivables, net Contract liabilities - current (120,207 ) (93,901 ) (26,306 ) Accounts payable Contract liabilities - noncurrent (25 ) (135 ) 110 Deferred credits and other liabilities - other Net contract assets $ 43,205 $ 10,203 $ 33,002 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 $10.3 million and $79.2 million in revenue for the three and nine months ended September 30, 2018 , respectively, which was previously included in contract liabilities at December 31, 2017 . 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. The Company recognized a net decrease in revenues of $8.7 million and $3.7 million for the three and nine months ended September 30, 2018 , respectively, from performance obligations satisfied in prior periods. Remaining performance obligations The remaining performance obligations at the construction materials and contracting and construction services segments include unrecognized revenues the Company reasonably expects to be realized which includes 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 remaining performance obligations at the pipeline and midstream segment include firm transportation and storage contracts with fixed pricing and fixed volumes. At September 30, 2019 , the Company's remaining performance obligations were $2.1 billion . The Company expects to recognize the following revenue amounts in future periods related to these remaining performance obligations: $1.6 billion within the next 12 months; $255.0 million within the next 13 to 24 months; and $249.6 million thereafter.

Business Combinations

Business Combinations	9 Months Ended
	Sep. 30, 2019
Business Acquisition [Line Items]
Business Combinations	Business combinations During 2019, the Company completed two acquisitions which were accounted for as business combinations. The following is a listing of the acquisitions made during 2019: • In March 2019, the Company acquired Viesko Redi-Mix, Inc., a provider of ready-mixed concrete in Oregon. The results of Viesko Redi-Mix, Inc. are included in the construction materials and contracting segment. • In September 2019, the Company purchased the assets of Pride Electric, Inc., an electrical construction company in Washington. The results of Pride Electric, Inc. are included in the construction services segment. All business combinations were accounted for in accordance with ASC 805 - Business Combinations . The results of the acquired businesses have been included in the Company's Consolidated Financial Statements beginning on the acquisition date. Pro forma financial amounts reflecting the effects of the business combinations are not presented, as these business combinations were not 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, estimated fair value of 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 2019 and 2018 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 one year 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. As of September 30, 2019, the gross aggregate consideration for acquisitions that occurred in 2019 was $54.5 million , subject to certain adjustments, and includes $1.2 million of debt assumed. The acquisitions are 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 Sheet for these adjustments are considered provisional until final settlement has occurred. The purchase price adjustments for Viesko Redi-Mix, Inc., have been settled and the purchase price allocation is considered final. During the third quarter of 2019, the Company finalized its valuation of the assets acquired and liabilities assumed in conjunction with the acquisition in 2018 of Sweetman Construction Company. As a result, measurement period adjustments were made to the previously disclosed provisional fair values. These adjustments did not have a material impact on the Company's consolidated results of operations. The purchase price adjustments for the three additional acquisitions in 2018 have been settled with no material adjustments made to the provisional accounting. The aggregate total consideration for the 2018 acquisitions and the final amounts allocated to the assets acquired and liabilities assumed were as follows: December 31, 2018 Measurement Period Adjustments September 30, 2019 (In thousands) Assets Current assets: Receivables, net $ 18,984 $ — $ 18,984 Inventories 10,329 (228 ) 10,101 Prepayments and other current assets 515 (14 ) 501 Total current assets 29,828 (242 ) 29,586 Property, plant and equipment 131,766 6,669 138,435 Deferred charges and other assets: Goodwill 33,131 (6,669 ) 26,462 Other Intangible assets, net 8,227 — 8,227 Other 927 — 927 Total deferred charges and other assets 42,285 (6,669 ) 35,616 Total assets acquired $ 203,879 $ (242 ) $ 203,637 Liabilities Current liabilities $ 11,122 $ (242 ) $ 10,880 Deferred credits and other liabilities: Asset retirement obligation 914 — 914 Deferred income taxes 5,565 — 5,565 Total deferred credits and other liabilities 6,479 — 6,479 Total liabilities assumed $ 17,601 $ (242 ) $ 17,359 Total consideration (fair value) $ 186,278 $ — $ 186,278

Discontinued operations

Discontinued operations	9 Months Ended
	Sep. 30, 2019
Discontinued Operations and Disposal Groups [Abstract]
Discontinued operations	Discontinued operations The assets and liabilities of the Company's discontinued operations have been classified as held for sale and the results of operations are shown in income (loss) from discontinued operations, other than certain general and administrative costs and interest expense which do not meet the criteria for income (loss) from discontinued operations. At the time the assets were classified as held for sale, depreciation, depletion and amortization expense was no longer recorded. Dakota Prairie Refining On June 24, 2016, WBI Energy entered into a membership interest purchase agreement with Tesoro to sell all the outstanding membership interests in Dakota Prairie Refining to Tesoro. WBI Energy and Calumet each previously owned 50 percent of the Dakota Prairie Refining membership interests and were equal members in building and operating Dakota Prairie Refinery. To effectuate the sale, WBI Energy acquired Calumet’s 50 percent membership interest in Dakota Prairie Refining on June 27, 2016. The sale of the membership interests to Tesoro closed on June 27, 2016. The sale of Dakota Prairie Refining reduced the Company’s risk by decreasing exposure to commodity prices. Fidelity In the second quarter of 2015, the Company began the marketing and sale process of Fidelity with an anticipated sale to occur within one year. Between September 2015 and March 2016, the Company entered into purchase and sale agreements to sell substantially all of Fidelity's oil and natural gas assets. The completion of these sales occurred between October 2015 and April 2016. In July 2018, the Company completed the sale of a majority of the remaining property, plant and equipment. The sale of Fidelity was part of the Company's strategic plan to grow its capital investments in the remaining business segments and to focus on creating a greater long-term value. Dakota Prairie Refining and Fidelity The carrying amounts of the major classes of assets and liabilities classified as held for sale on the Consolidated Balance Sheets were as follows: September 30, 2019 September 30, 2018 December 31, 2018 (In thousands) Assets Current assets: Receivables, net $ 426 $ 571 $ 430 Income taxes receivable (a) — 1,640 — Total current assets held for sale 426 2,211 430 Noncurrent assets: Deferred income taxes 1,926 1,711 1,926 Other 161 161 161 Total noncurrent assets held for sale 2,087 1,872 2,087 Total assets held for sale $ 2,513 $ 4,083 $ 2,517 Liabilities Current liabilities: Accounts payable $ — $ 188 $ 80 Taxes payable 1,300 7,463 1,451 Other accrued liabilities 2,093 1,948 2,470 Total current liabilities held for sale 3,393 9,599 4,001 Noncurrent liabilities: Deferred income taxes (b) — 37 — Total noncurrent liabilities held for sale — 37 — Total liabilities held for sale $ 3,393 $ 9,636 $ 4,001 (a) On the Company's Consolidated Balance Sheets, these amounts were reclassified to taxes payable and are reflected in current liabilities held for sale. (b) On the Company's Consolidated Balance Sheets, these amounts were reclassified to deferred charges and other assets - deferred income taxes and are reflected in noncurrent assets held for sale. The reconciliation of the major classes of income and expense constituting pretax income (loss) from discontinued operations to the after-tax income (loss) from discontinued operations on the Consolidated Statements of Income was as follows: Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 (In thousands) Operating revenues $ 230 $ 61 $ 298 $ 201 Operating expenses (1,760 ) 216 264 825 Operating income (loss) 1,990 (155 ) 34 (624 ) Other income — — — 12 Interest expense — — — 575 Income (loss) from discontinued operations before income taxes 1,990 (155 ) 34 (1,187 ) Income taxes 481 (37 ) 8 (1,272 ) Income (loss) from discontinued operations $ 1,509 $ (118 ) $ 26 $ 85

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Leases of Lessee Disclosure [Text Block]	Leases Most of the leases the Company enters into are for equipment, buildings, easements and vehicles as part of their ongoing operations. The Company also leases certain equipment to third parties through its utility and construction services segments. The Company determines if an arrangement contains a lease at inception of a contract and accounts for all leases in accordance with ASC 842 - Leases. For more information on the adoption of ASC 842, see Note 6 . The recognition of leases requires the Company to make estimates and assumptions that affect the lease classification and the assets and liabilities recorded. The accuracy of lease assets and liabilities reported on the Consolidated Financial Statements depends on, among other things, management's estimates of interest rates used to discount the lease assets and liabilities to their present value, as well as the lease terms based on the unique facts and circumstances of each lease. Lessee accounting The leases the Company has entered into as part of its ongoing operations are considered operating leases and are recognized on the balance sheet as right-of-use assets, current lease liabilities and, if applicable, noncurrent lease liabilities. Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The Company determines the lease term based on the non-cancelable and cancelable periods in each contract. The non-cancelable period consists of the term of the contract that is legally enforceable and cannot be canceled by either party without incurring a significant penalty. The cancelable period is determined by various factors that are based on who has the right to cancel a contract. If only the lessor has the right to cancel the contract, the Company will assume the contract will continue. If the lessee is the only party that has the right to cancel the contract, the Company looks to asset, entity and market-based factors. If both the lessor and the lessee have the right to cancel the contract, the Company assumes the contract will not continue. Generally, the leases for vehicles and equipment have a term of five years or less and buildings and easements have a longer term of up to 35 years or more. To date, the Company does not have any residual value guarantee amounts probable of being owed to a lessor, financing leases or material agreements with related parties. The Company has elected to recognize leases with an original lease term of 12 months or less in income on a straight-line basis over the term of the lease and not recognize a corresponding right-of-use asset or lease liability. Lease costs are included in operation and maintenance expense on the Company's Consolidated Statements of Income. The discount rate used to calculate the present value of the lease liabilities is based upon the implied rate within each contract. If the rate is unknown or cannot be determined, the Company uses an incremental borrowing rate which is determined by the length of the contract, asset class and the Company's borrowing rates as of the commencement date of the contract. The following tables provide information on the Company's operating leases: Three Months Ended Nine Months Ended September 30, September 30, 2019 2019 (In thousands) Lease costs: Operating lease cost $ 10,536 $ 32,444 Variable lease cost 381 1,180 Short-term lease cost 28,270 85,982 Total lease costs $ 39,187 $ 119,606 September 30, 2019 (Dollars in thousands) Weighted average remaining lease term 2.98 years Weighted average discount rate 4.63 % Cash paid for amounts included in the measurement of lease liabilities $ 32,261 The reconciliation of the future undiscounted cash flows to the operating lease liabilities presented on the Company's Consolidated Balance Sheet at September 30, 2019 , was as follows: (In thousands) Remainder of 2019 $ 10,619 2020 32,605 2021 23,488 2022 15,838 2023 9,913 Thereafter 54,765 Total 147,228 Less discount 28,478 Total operating lease liabilities $ 118,750 As previously disclosed in the 2018 Annual Report, the undiscounted annual minimum lease payments due under the Company's leases following the previous lease accounting standard as of December 31, 2018, were as follows: 2019 2020 2021 2022 2023 Thereafter (In thousands) Operating leases $ 37,740 $ 26,255 $ 17,868 $ 11,647 $ 7,278 $ 49,098
Leases of Lessor Disclosure [Text Block]	Lessor accounting The Company leases certain equipment to third parties which are considered operating leases. 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. The majority of the Company's operating leases are short-term leases of less than 12 months. At September 30, 2019 , the Company had $10.0 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, 2019
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: Nine Months Ended September 30, 2019 Balance at January 1, 2019 Goodwill Acquired the Year Measurement Period Adjustments 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 Nine Months Ended September 30, 2018 Balance at January 1, 2018 Goodwill Acquired the Year Measurement Period Adjustments Balance at September 30, 2018 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 176,290 8,412 — 184,702 Construction services 109,765 — — 109,765 Total $ 631,791 $ 8,412 $ — $ 640,203 Year Ended December 31, 2018 Balance at January 1, 2018 Goodwill Acquired the Year Measurement Period Adjustments Balance at December 31, 2018 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 176,290 33,131 — 209,421 Construction services 109,765 — — 109,765 Total $ 631,791 $ 33,131 $ — $ 664,922 During 2019 and 2018, the Company completed two and four business combinations, respectively, and the results of these acquisitions have been included in the Company's construction materials and contracting and construction services segments. These business combinations increased the construction materials and contracting segment's goodwill balance at September 30, 2019 and 2018, and December 31, 2018, and increased the construction services segment's goodwill balance at September 30, 2019, as noted in the previous tables. As a result of the business combinations, other intangible assets increased $6.3 million at September 30, 2019, compared to December 31, 2018. For more information related to these business combinations, see Note 9 . Other amortizable intangible assets were as follows: September 30, 2019 September 30, 2018 December 31, 2018 (In thousands) Customer relationships $ 18,011 $ 15,920 $ 22,720 Less accumulated amortization 5,823 13,342 13,535 12,188 2,578 9,185 Noncompete agreements 3,419 2,606 2,605 Less accumulated amortization 1,868 1,911 1,956 1,551 695 649 Other 7,488 6,458 6,458 Less accumulated amortization 5,716 5,413 5,477 1,772 1,045 981 Total $ 15,511 $ 4,318 $ 10,815 Amortization expense for amortizable intangible assets for the three and nine months ended September 30, 2019 , was $500,000 and $1.6 million , respectively. Amortization expense for amortizable intangible assets for the three and nine months ended September 30, 2018 , was $300,000 and $900,000 , respectively. Estimated amortization expense for identifiable intangible assets as of September 30, 2019 , was: Remainder of 2019 2020 2021 2022 2023 Thereafter (In thousands) Amortization expense $ 931 $ 3,077 $ 2,042 $ 1,996 $ 1,957 $ 5,508

Regulatory assets and liabiliti

Regulatory assets and liabilities	9 Months Ended
	Sep. 30, 2019
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	Regulatory assets and liabilities The following table summarizes the individual components of unamortized regulatory assets and liabilities: Estimated Recovery Period * September 30, 2019 December 31, 2018 (In thousands) Regulatory assets: Pension and postretirement benefits (a) (e) $ 165,843 $ 165,898 Natural gas costs recoverable through rate adjustments (a) (b) Up to 3 years 93,001 42,652 Asset retirement obligations (a) Over plant lives 64,771 60,097 Cost recovery mechanisms (a) (b) Up to 4 years 20,912 17,948 Manufactured gas plant site remediation (a) - 15,739 17,068 Taxes recoverable from customers (a) Over plant lives 11,600 11,946 Plants to be retired (a) - 26,152 — Conservation programs (b) Up to 1 year 9,467 7,494 Long-term debt refinancing costs (a) Up to 19 years 4,439 4,898 Costs related to identifying generation development (a) Up to 8 years 2,166 2,508 Other (a) (b) Up to 20 years 17,501 9,608 Total regulatory assets $ 431,591 $ 340,117 Regulatory liabilities: Taxes refundable to customers (c) (d) $ 258,012 $ 277,833 Plant removal and decommissioning costs (c) (d) 176,016 173,143 Natural gas costs refundable through rate adjustments (d) 19,194 29,995 Pension and postretirement benefits (c) 12,942 15,264 Other (c) (d) 24,153 25,197 Total regulatory liabilities $ 490,317 $ 521,432 Net regulatory position $ (58,726 ) $ (181,315 ) * Estimated recovery period for regulatory assets currently being recovered in rates charged to customers. (a) Included in deferred charges and other assets - other on the Consolidated Balance Sheets. (b) Included in prepayments and other current assets on the Consolidated Balance Sheets. (c) Included in deferred credits and other liabilities - other on the Consolidated Balance Sheets. (d) Included in other accrued liabilities on the Consolidated Balance Sheets. (e) Recovered as expense is incurred or cash contributions are made. The regulatory assets are expected to be recovered in rates charged to customers. A portion of the Company's regulatory assets are not earning a return; however, these regulatory assets are expected to be recovered from customers in future rates. As of September 30, 2019 and December 31, 2018 , approximately $278.2 million and $313.5 million , respectively, of regulatory assets were not earning a rate of return. During the first quarter of 2019 and the fourth quarter of 2018, the Company experienced increased natural gas costs in certain jurisdictions where it supplies natural gas. The Company has recorded these natural gas costs as regulatory assets as they are expected to be recovered from customers, as discussed in Note 19 . In February 2019, the Company announced that it intends to retire three aging coal-fired electric generation units within the next three years. 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, 2019
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 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 $84.2 million , $80.4 million and $73.8 million , at September 30, 2019 and 2018 , and December 31, 2018 , respectively, are classified as investments on the Consolidated Balance Sheets. 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 net unrealized gains on these investments were $2.1 million and $3.0 million for the three and nine months ended September 30, 2018 , 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. The available-for-sale securities 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 loss. Details of available-for-sale securities were as follows: September 30, 2019 Cost Gross Unrealized Gains Gross Unrealized Losses 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 September 30, 2018 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,550 $ 3 $ 251 $ 10,302 U.S. Treasury securities 179 — — 179 Total $ 10,729 $ 3 $ 251 $ 10,481 December 31, 2018 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,473 $ 21 $ 162 $ 10,332 U.S. Treasury securities 179 — — 179 Total $ 10,652 $ 21 $ 162 $ 10,511 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. For the nine months ended September 30, 2019 and 2018 , there were no transfers between Levels 1 and 2. The Company's assets and liabilities measured at fair value on a recurring basis were as follows: Fair Value Measurements at September 30, 2019, Using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) 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 September 30, 2018, Using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Balance at September 30, 2018 (In thousands) Assets: Money market funds $ — $ 9,948 $ — $ 9,948 Insurance contract* — 80,358 — 80,358 Available-for-sale securities: Mortgage-backed securities — 10,302 — 10,302 U.S. Treasury securities — 179 — 179 Total assets measured at fair value $ — $ 100,787 $ — $ 100,787 * The insurance contract invests approximately 47 percent in fixed-income investments, 24 percent in common stock of large-cap companies, 13 percent in common stock of mid-cap companies, 12 percent in common stock of small-cap companies, 3 percent in target date investments and 1 percent in cash equivalents. Fair Value Measurements at December 31, 2018, Using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Balance at December 31, 2018 (In thousands) Assets: Money market funds $ — $ 10,799 $ — $ 10,799 Insurance contract* — 73,838 — 73,838 Available-for-sale securities: Mortgage-backed securities — 10,332 — 10,332 U.S. Treasury securities — 179 — 179 Total assets measured at fair value $ — $ 95,148 $ — $ 95,148 * 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. 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. The 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'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 long-term debt was as follows: Carrying Amount Fair Value (In thousands) Long-term debt at September 30, 2019 $ 2,246,756 $ 2,450,209 Long-term debt at September 30, 2018 $ 1,915,470 $ 1,987,360 Long-term debt at December 31, 2018 $ 2,108,695 $ 2,183,819 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, 2019
Debt Disclosure [Abstract]
Debt	Debt Certain debt instruments of the Company's subsidiaries contain restrictive covenants and cross-default provisions. In order to borrow under the respective debt instruments, 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, 2019 . 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 their respective 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 the construction businesses. Short-term debt The following describes certain transactions during the three and nine months ended September 30, 2019, included in outstanding short-term debt: • On March 22, 2019, Cascade entered into a $40.0 million term loan agreement with a variable interest rate and a maturity date of December 31, 2019. • On April 12, 2019, Centennial entered into a $50.0 million term loan agreement with a variable interest rate and a maturity date of April 11, 2020. • On August 7, 2019, Centennial entered into a $50.0 million term loan agreement with a variable interest rate and a maturity date of January 31, 2020. Long-term debt The following describes certain transactions during the three and nine months ended September 30, 2019, included in outstanding long-term debt: • On April 4, 2019, Centennial issued $150.0 million of senior notes with maturity dates ranging from April 4, 2029 to April 4, 2034, at a weighted average interest rate of 4.60 percent. • On June 7, 2019, Cascade amended its revolving credit agreement to increase the borrowing limit from $75.0 million to $100.0 million and extend the termination date from April 24, 2020 to June 7, 2024. • On June 7, 2019, Intermountain amended its revolving credit agreement to extend the termination date from April 24, 2020 to June 7, 2024. • On June 13, 2019, Cascade issued $75.0 million of senior notes with maturity dates ranging from June 13, 2029 to June 13, 2049, at a weighted average interest rate of 3.93 percent. • On June 13, 2019, Intermountain issued $50.0 million of senior notes with maturity dates ranging from June 13, 2029 to June 13, 2049, at a weighted average interest rate of 3.92 percent. Long-term Debt Outstanding Long-term debt outstanding was as follows: Weighted Average Interest Rate at September 30, 2019 September 30, 2019 December 31, 2018 (In thousands) Senior notes due on dates ranging from December 15, 2019 to January 15, 2055 4.52 % $ 1,655,000 $ 1,381,000 Commercial paper supported by revolving credit agreements 2.46 % 281,800 338,100 Term loan agreements due on dates ranging from September 3, 2032 to November 18, 2059 2.75 % 209,100 209,800 Credit agreements due on June 7, 2024 4.66 % 31,000 110,100 Medium-term notes due on dates ranging from September 1, 2020 to March 16, 2029 6.68 % 50,000 50,000 Other notes due on dates ranging from July 15, 2021 to November 30, 2038 5.01 % 26,083 25,229 Less unamortized debt issuance costs 6,074 5,207 Less discount 153 327 Total long-term debt 2,246,756 2,108,695 Less current maturities 65,810 251,854 Net long-term debt $ 2,180,946 $ 1,856,841 Schedule of Debt Maturities Long-term debt maturities, which excludes unamortized debt issuance costs and discount, as of September 30, 2019 , were as follows: Remainder of 2019 2020 2021 2022 2023 Thereafter (In thousands) Long-term debt maturities $ 50,110 $ 15,902 $ 204,522 $ 147,402 $ 155,502 $ 1,679,545

Cash flow information

Cash flow information	9 Months Ended
	Sep. 30, 2019
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, 2019 2018 (In thousands) Interest, net* $ 64,596 $ 58,359 Income taxes paid, net** $ 1,816 $ 8,887 * AFUDC - borrowed was $2.0 million and $1.8 million for the nine months ended September 30, 2019 and 2018 , respectively. ** Income taxes paid, including discontinued operations, were $2.0 million and $5.1 million for the nine months ended September 30, 2019 and 2018 , respectively. Noncash investing and financing transactions were as follows: September 30, 2019 September 30, 2018 December 31, 2018 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 46,770 $ — $ — Property, plant and equipment additions in accounts payable $ 34,368 $ 34,594 $ 42,355 Debt assumed in connection with a business combination $ 1,163 $ — $ — Issuance of common stock in connection with a business combination $ — $ 17,993 $ 18,186

Business segment data

Business segment data	9 Months Ended
	Sep. 30, 2019
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 and midstream segment provides natural gas transportation, underground storage and gathering services through regulated and nonregulated 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 and 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 governmental customers. The Other category includes the activities of Centennial Capital, which, through its subsidiary InterSource Insurance Company, insures various types of risks as a captive insurer for certain of the Company's subsidiaries. The function of the captive insurer is to fund the self-insured layers of the insured Company's general liability, automobile liability, pollution liability and other coverages. Centennial Capital also owns certain real and personal property. In addition, the Other category includes certain assets, liabilities and tax adjustments of the holding company primarily associated with corporate functions and certain general and administrative costs (reflected in operation and maintenance expense) and interest expense which were previously allocated to the refining business and Fidelity that 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 Dakota Prairie Refining and Fidelity other than certain general and administrative costs and interest expense as described above. For more information on discontinued operations, see Note 10 . The information below follows the same accounting policies as described in Note 1 of the Company's Notes to Consolidated Financial Statements in the 2018 Annual Report. Information on the Company's segments was as follows: Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 (In thousands) External operating revenues: Regulated operations: Electric $ 89,845 $ 86,080 $ 263,423 $ 251,984 Natural gas distribution 93,642 92,248 569,656 554,452 Pipeline and midstream 25,957 22,289 52,230 45,325 209,444 200,617 885,309 851,761 Nonregulated operations: Pipeline and midstream 6,576 6,782 17,597 16,640 Construction materials and contracting 869,376 743,763 1,692,287 1,466,435 Construction services 478,381 329,578 1,363,305 986,649 Other 22 47 65 193 1,354,355 1,080,170 3,073,254 2,469,917 Total external operating revenues $ 1,563,799 $ 1,280,787 $ 3,958,563 $ 3,321,678 Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 (In thousands) Intersegment operating revenues: Regulated operations: Electric $ — $ — $ — $ — Natural gas distribution — — — — Pipeline and midstream 3,750 3,070 35,098 31,252 3,750 3,070 35,098 31,252 Nonregulated operations: Pipeline and midstream 81 117 200 233 Construction materials and contracting 124 165 388 501 Construction services 1,226 782 2,076 1,332 Other 2,862 3,037 13,566 8,343 4,293 4,101 16,230 10,409 Intersegment eliminations (8,043 ) (7,171 ) (51,328 ) (41,661 ) Total intersegment operating revenues $ — $ — $ — $ — Operating income (loss): Electric $ 21,930 $ 21,140 $ 49,708 $ 52,321 Natural gas distribution (15,565 ) (11,665 ) 32,132 32,503 Pipeline and midstream 11,416 9,036 32,017 25,687 Construction materials and contracting 143,024 109,598 147,622 120,591 Construction services 29,950 11,863 89,381 51,853 Other (1,285 ) 32 140 417 Total operating income $ 189,470 $ 140,004 $ 351,000 $ 283,372 Net income (loss): Regulated operations: Electric $ 16,291 $ 15,284 $ 39,267 $ 37,500 Natural gas distribution (15,625 ) (11,887 ) 14,623 13,884 Pipeline and midstream 6,933 10,109 20,316 20,809 7,599 13,506 74,206 72,193 Nonregulated operations: Pipeline and midstream 801 848 1,380 1,136 Construction materials and contracting 102,611 78,876 97,328 79,691 Construction services 21,113 9,278 63,982 38,457 Other 4,004 4,861 3,466 1,928 128,529 93,863 166,156 121,212 Income from continuing operations 136,128 107,369 240,362 193,405 Income (loss) from discontinued operations, net of tax 1,509 (118 ) 26 85 Net income $ 137,637 $ 107,251 $ 240,388 $ 193,490

Employee benefit plans

Employee benefit plans	9 Months Ended
	Sep. 30, 2019
Retirement Benefits [Abstract]
Pension and other postretirement benefit plans	Employee benefit plans Pension and other postretirement plans The Company has noncontributory qualified defined benefit pension plans and other postretirement benefit plans for certain eligible employees. Components of net periodic benefit cost (credit) for the Company's pension and other postretirement benefit plans were as follows: Pension Benefits Other Postretirement Benefits Three Months Ended September 30, 2019 2018 2019 2018 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 286 $ 374 Interest cost 3,806 3,648 746 725 Expected return on assets (4,559 ) (5,188 ) (1,201 ) (1,217 ) Amortization of prior service credit — — (289 ) (349 ) Amortization of net actuarial loss 1,387 1,751 27 160 Net periodic benefit cost (credit), including amount capitalized 634 211 (431 ) (307 ) Less amount capitalized — — 26 46 Net periodic benefit cost (credit) $ 634 $ 211 $ (457 ) $ (353 ) Pension Benefits Other Postretirement Benefits Nine Months Ended September 30, 2019 2018 2019 2018 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 857 $ 1,121 Interest cost 11,419 10,943 2,239 2,175 Expected return on assets (13,677 ) (15,565 ) (3,603 ) (3,650 ) Amortization of prior service credit — — (866 ) (1,046 ) Amortization of net actuarial loss 4,160 5,254 82 480 Net periodic benefit cost (credit), including amount capitalized 1,902 632 (1,291 ) (920 ) Less amount capitalized — — 84 128 Net periodic benefit cost (credit) $ 1,902 $ 632 $ (1,375 ) $ (1,048 ) 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, 2019 , was $1.1 million and $3.3 million , respectively. The Company's net periodic benefit cost for these plans for the three and nine months ended September 30, 2018 , was $1.1 million and $3.3 million , respectively. The components of net periodic benefit cost for these plans, which does not contain any service costs, are included in other income on the Consolidated Statements of Income.

Regulatory matters

Regulatory matters	9 Months Ended
	Sep. 30, 2019
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. The Company's most recent cases by jurisdiction are discussed in the following paragraphs. MNPUC On April 18, 2019, the MNPUC approved a decrease in rates for Great Plains of $400,000 on an annual basis to reflect TCJA impacts effective May 1, 2019, as well as a one-time TCJA refund of approximately $600,000 for the period from January 1, 2018 through April 30, 2019. The refunds were credited to customers' bills between August 14, 2019 and September 16, 2019. 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. Great Plains also requested an interim increase of approximately $2.6 million or approximately 11.0 percent, subject to refund. This matter is pending before the MNPUC. MTPSC On July 31, 2019, the MTPSC approved an electric rate increase that was primarily to recover Montana-Dakota's investments in facilities to enhance safety and reliability and the depreciation and taxes associated with such investments, partially offset by the impacts of TCJA. The approved rates included a $9.0 million annual increase implemented on September 1, 2019, and an additional $300,000 annual increase to be implemented beginning 12 months after the date of approval. NDPSC On October 22, 2019, the NDPSC approved an increase in rates to recover approximately $1.5 million annually for the revenue requirements on certain of Montana-Dakota's electric transmission projects through its transmission cost adjustment rate. The rates were effective October 28, 2019. On August 28, 2019, Montana-Dakota filed an application with the NDPSC for an advanced determination of prudence and a certificate of public convenience and necessity to construct, own and operate Heskett Unit 4, an 88-MW simple-cycle natural gas-fired combustion turbine peaking unit at Heskett Station near Mandan, North Dakota. This matter is pending before the NDPSC. On September 16, 2019, Montana-Dakota submitted an application with the NDPSC requesting the use of deferred accounting for the treatment of costs related to the retirement of Lewis & Clark Station in Sidney, Montana, and units 1 and 2 at Heskett Station near Mandan, North Dakota. This matter is pending before the NDPSC. OPUC On December 29, 2017, Cascade filed a request with the OPUC to use deferred accounting for the 2018 net benefits associated with the implementation of the TCJA. On September 12, 2019, the OPUC approved the request, including a settlement to refund to customers $1.4 million related to TJCA impacts for the period from January 2018 through March 2019. These refunds will be reflected in customers' rates over a 12-month period beginning November 1, 2019. On June 14, 2019, Cascade filed a request with the OPUC to implement a new pipeline safety cost recovery mechanism to recover investments to replace Cascade's highest risk infrastructure. If approved, Cascade would file a report annually with the OPUC detailing actual projects undertaken and costs incurred for the year on November 1, seeking recovery for investments from January 1 through December 31 of that same year. This matter is pending before the OPUC. WUTC On March 29, 2019, Cascade filed a general rate case with the WUTC requesting an increase in annual revenue of $12.7 million or approximately 5.5 percent. On September 20, 2019, Cascade filed a joint settlement agreement with the WUTC reflecting a revised annual increase of $6.5 million or approximately 2.8 percent. A hearing on the settlement is scheduled for November 5, 2019. This matter is pending before the WUTC. On May 31, 2019, Cascade filed its annual pipeline cost recovery mechanism requesting an increase in revenue of approximately $1.6 million or approximately 0.7 percent. On October 10, 2019, Cascade filed its final update to the cost recovery mechanism with a revised increase in revenue of approximately $440,000 or approximately 0.2 percent. On October 24, 2019, the WUTC approved the increase with rates effective for services provided on or after November 1, 2019. On September 13, 2019, Cascade filed its annual purchased gas adjustment with the WUTC requesting an annual increase of approximately $12.8 million or approximately 5.7 percent for a period of three years . The requested increase is primarily due to unrecovered purchased gas costs as a result of the rupture of the Enbridge pipeline in Canada on October 9, 2018, causing increased natural gas costs. On October 24, 2019, the WUTC approved the increase with rates effective for services provided on or after November 1, 2019. WYPSC On April 4, 2019, Montana-Dakota submitted compliance rates to the WYPSC reflecting a decrease in annual revenues of approximately $1.1 million or approximately 4.2 percent to reflect TCJA impacts. On April 8, 2019, the WYPSC approved the Company's requested decrease in electric rates and required a refund to customers for the period from January 1, 2018 through the date prior to the implementation of the rates within 90 days of the effective date of the new rates. The new rates were implemented for service rendered on and after May 1, 2019, and the refunds of approximately $1.6 million were credited to customers' bills on July 25, 2019. On March 30, 2018, Montana-Dakota reported its natural gas earnings do not support a decrease in rates and requested the WYPSC allow the impacts of the TCJA be addressed in a natural gas rate case to be submitted by June 1, 2019. On September 12, 2019, the WYPSC approved a one-time refund of approximately $200,000 to be credited to customers' bills by November 1, 2019, for the TCJA impacts from January 1, 2018 through June 30, 2019. On May 23, 2019, Montana-Dakota filed an application with the WYPSC for a natural gas rate increase of approximately $1.1 million annually or approximately 7.0 percent above current rates. The requested increase was to recover increased operating expenses and investments in distribution facilities to improve system safety and reliability. This matter is pending before the WYPSC. FERC In accordance with WBI Energy Transmission’s offer of settlement and stipulation and agreement with the FERC dated June 4, 2014, the Company was to make a filing with new proposed rates to be effective no later than May 1, 2019. On October 31, 2018, the Company filed a rate case with the FERC. Following negotiations between FERC staff, customers and the Company, on May 30, 2019, the FERC granted the Company's request to place interim settlement rates into effect May 1, 2019, subject to refund or surcharge, and pending the FERC's consideration of the filing of a settlement agreement. Based on as filed volumes and settlement rates, the revenue increase is approximately $4.5 million annually. Included in the revenue increase are the impacts from higher depreciation rates agreed to in the settlement, as well as the impacts of the TCJA. On June 28, 2019, the Company filed a final settlement agreement and related documents with the FERC. On September 30, 2019, the FERC approved the final settlement agreement and related documents. On August 29, 2019, Montana-Dakota filed an update to its transmission formula rate under the MISO tariff for the multivalue project for $13.4 million , which is effective January 1, 2020.

Contingencies

Contingencies	9 Months Ended
	Sep. 30, 2019
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, 2019 and 2018 , and December 31, 2018 , the Company accrued liabilities which have not been discounted, including liabilities held for sale, of $30.6 million , $30.4 million and $30.4 million , respectively. 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 Portland Harbor Site In December 2000, Knife River - Northwest was named by the EPA as a PRP in connection with the cleanup of the Willamette River site adjacent to a commercial property site acquired by Knife River - Northwest from Georgia-Pacific West, Inc. The riverbed site is part of the Portland, Oregon, Harbor Superfund Site where the EPA wants responsible parties to share in the costs of cleanup. To date, costs of the overall remedial investigation and feasibility study of the harbor site are being recorded, and initially paid, through an administrative consent order by the LWG. Investigative costs are indicated to be in excess of $100 million . Remediation is expected to take up to 13 years with a present value cost estimate of approximately $1 billion . Corrective action will not be taken until remedial design/remedial action plans are approved by the EPA. Knife River - Northwest was also notified that the Portland Harbor Natural Resource Trustee Council intends to perform an injury assessment to natural resources resulting from the release of hazardous substances at the Harbor Superfund Site. It is not possible to estimate the costs of natural resource damages until an assessment is completed and allocations are undertaken. At this time, Knife River - Northwest does not believe it is a responsible party and has notified Georgia-Pacific West, Inc., that it intends to seek indemnity for liabilities incurred in relation to the above matters pursuant to the terms of their sale agreement. Knife River - Northwest has entered into an agreement tolling the statute of limitations in connection with the LWG's potential claim for contribution to the costs of the remedial investigation and feasibility study. LWG has stated its intent to file suit against Knife River - Northwest and others to recover LWG's investigation costs to the extent Knife River - Northwest cannot demonstrate its non-liability for the contamination or is unwilling to participate in an alternative dispute resolution process that has been established to address the matter. At this time, Knife River - Northwest has agreed to participate in the alternative dispute resolution process. The Company believes it is not probable that it will incur any material environmental remediation costs or damages in relation to the above referenced matter. Manufactured Gas Plant Sites Claims have been made against Cascade for cleanup of environmental contamination at manufactured gas plant sites operated by Cascade's predecessors and a similar claim has been made against Montana-Dakota for a site operated by Montana-Dakota and its predecessors. Any accruals related to these claims are reflected in regulatory assets. For more information, see Note 13 . Demand has been made of Montana-Dakota to participate in investigation and remediation of environmental contamination at a site in Missoula, Montana. The site operated as a former manufactured gas plant from approximately 1907 to 1938 when it was converted to a butane-air plant that operated until 1956. Montana-Dakota or its predecessors owned or controlled the site for a period of the time it operated as a manufactured gas plant and Montana-Dakota operated the butane-air plant from 1940 to 1951, at which time it sold the plant. There are no documented wastes or by-products resulting from the mixing or distribution of butane-air gas. Preliminary assessment of a portion of the site provided a recommended remedial alternative for that portion of approximately $560,000 . However, the recommended remediation would not address any potential contamination to adjacent parcels that may be impacted by contamination from the manufactured gas plant. Montana-Dakota and another party agreed to voluntarily investigate and remediate the site and that Montana-Dakota will pay two-thirds of the costs for further investigation and remediation of the site. Montana-Dakota received notice from a prior insurance carrier that it will participate in payment of defense costs incurred in relation to the claim. Montana-Dakota has accrued $375,000 for the remediation of this site. 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 confirms that contaminants have affected soil and groundwater at the site, as well as sediments in the adjacent Port Washington Narrows. Alternative remediation options have been identified with preliminary cost estimates ranging from $340,000 to $6.4 million . Data developed through the assessment and previous investigations indicates the contamination likely derived from multiple, different sources and multiple current and former owners of properties and businesses in the vicinity of the site may be responsible for the contamination. 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 has 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 $3.8 million has been incurred. Cascade has accrued $3.8 million for the remedial investigation and feasibility study, as well as $6.4 million for remediation of this site; however, the accrual for remediation costs will be reviewed and adjusted, if necessary, after completion of the remedial investigation and 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. A claim was made against Cascade for contamination at a site in Bellingham, Washington. Cascade received notice from a party in May 2008 that Cascade may be a PRP, along with other parties, for contamination from a manufactured gas plant owned by Cascade and its predecessor from about 1946 to 1962. Other PRPs reached an agreed order and work plan with the Washington DOE for completion of a remedial investigation and feasibility study for the site. A feasibility study prepared for one of the PRPs in March 2018 identifies five cleanup action alternatives for the site with estimated costs ranging from $8.0 million to $20.4 million with a selected preferred alternative having an estimated total cost of $9.3 million . The other PRPs will develop a cleanup action plan and, after public review of the cleanup action plan, develop design documents. Cascade believes its proportional share of any liability will be relatively small in comparison to other PRPs. The plant manufactured gas from coal between approximately 1890 and 1946. In 1946, shortly after Cascade's predecessor acquired the plant, it converted the plant to a propane-air gas facility. There are no documented wastes or by-products resulting from the mixing or distribution of propane-air gas. Cascade has recorded an accrual for this site for an amount that is not material. Cascade has received notices from and entered into agreement with certain of its insurance carriers that they will participate in defense of Cascade for certain of the 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, Cascade intends to seek recovery through the OPUC and WUTC of remediation costs in 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 who were the sellers in three purchase and sale agreements for periods ranging up to 10 years from the date of sale. 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, 2019 , the fixed maximum amounts guaranteed under these agreements aggregated $206.5 million . At September 30, 2019 , the amounts of scheduled expiration of the maximum amounts guaranteed under these agreements aggregate to $2.0 million in 2019 ; $192.2 million in 2020 ; $700,000 in 2021 ; $500,000 in 2022 ; $500,000 in 2023 ; $1.6 million thereafter; $9.0 million , which has no scheduled maturity date; and no amounts were outstanding. 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, 2019 , the fixed maximum amounts guaranteed under these letters of credit aggregated $30.0 million . At September 30, 2019 , the amounts of scheduled expiration of the maximum amounts guaranteed under these letters of credit aggregate to $24.4 million in 2019 and $5.6 million in 2020 with no amounts outstanding. 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, 2019 . 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, 2019 , approximately $930.1 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 Company's 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, 2019 , 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 $36.6 million .

Basis of presentation (Policies

Basis of presentation (Policies)	9 Months Ended
	Sep. 30, 2019
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 2018 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.

Accounts receivable and allow_2

Accounts receivable and allowance for doubtful accounts (Policies)	9 Months Ended
	Sep. 30, 2019
Receivables [Abstract]
Accounts receivable and allowance for doubtful accounts	Accounts receivable consists primarily of trade receivables from the sale of goods and services which are recorded at the invoiced amount net of allowance for doubtful accounts, and costs and estimated earnings in excess of billings on uncompleted contracts.The allowance for doubtful accounts is determined through a review of past due balances and other specific account data. 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, 2019
Inventory Disclosure [Abstract]
Inventories and natural gas in storage	Natural gas in storage for the Company's regulated operations is generally carried at lower of cost or net realizable value, or cost using the last-in, first-out method. All other inventories are stated at the lower of cost or net realizable value.

Earnings per common share (Poli

Earnings per common share (Policies)	9 Months Ended
	Sep. 30, 2019
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.

New accounting standards (Polic

New accounting standards (Policies)	9 Months Ended
	Sep. 30, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New accounting standards	Recently adopted accounting standards ASU 2016-02 - Leases In February 2016, the FASB issued guidance regarding leases. The guidance required lessees to recognize a lease liability and a right-of-use asset on the balance sheet for operating and financing leases. The guidance remained largely the same for lessors, although some changes were made to better align lessor accounting with the new lessee accounting and to align with the revenue recognition standard. The guidance also required additional disclosures, both quantitative and qualitative, related to operating and financing leases for the lessee and sales-type, direct financing and operating leases for the lessor. The Company adopted the standard on January 1, 2019. In July 2018, the FASB issued ASU 2018-11 - Leases: Targeted Improvements , an accounting standard update to ASU 2016-02. This ASU provided an entity the option to adopt the guidance using one of two modified retrospective approaches. An entity could adopt the guidance using the modified retrospective transition approach beginning in the earliest year presented in the financial statements. This method of adoption would have required the restatement of prior periods reported and the presentation of lease disclosures under the new guidance for all periods reported. The additional transition method of adoption, introduced by ASU 2018-11, allowed entities the option to apply the guidance on the date of adoption by recognizing a cumulative effect adjustment to retained earnings during the period of adoption and did not require prior comparative periods to be restated. The Company adopted the standard on January 1, 2019, utilizing the additional transition method of adoption applied on the date of adoption and the practical expedient that allowed the Company to not reassess whether an expired or existing contract contained a lease, the classification of leases or initial direct costs. The Company did not identify any cumulative effect adjustments. The Company also adopted a short-term leasing policy as the lessee where leases with a term of 12 months or less are not included on the Consolidated Balance Sheet. As a practical expedient, a lessee may choose not to separate nonlease components from lease components and instead account for lease and nonlease components as a single lease component. The election shall be made by asset class. The Company has elected to adopt the lease/nonlease component practical expedient for all asset classes as the lessee. The Company did not elect the practical expedient to use hindsight when assessing the lease term or impairment of right-of-use assets for the existing leases on the date of adoption. In January 2018, the FASB issued a practical expedient for land easements under the new lease guidance. The practical expedient permits an entity to elect the option to not evaluate land easements under the new guidance if they existed or expired before the adoption of the new lease guidance and were not previously accounted for as leases under the previous lease guidance. Once an entity adopts the new guidance, the entity should apply the new guidance on a prospective basis to all new or modified land easements. The Company has adopted this practical expedient. The Company formed a lease implementation team to review and assess existing contracts to identify and evaluate those containing leases. Additionally, the team implemented new and revised existing software to meet the reporting and disclosure requirements of the standard. The Company also assessed the impact the standard had on its processes and internal controls and identified new and updated existing internal controls and processes to ensure compliance with the new lease standard; such modifications were not deemed to be significant. During the assessment phase, the Company used various surveys, reconciliations and analytic methodologies to ensure the completeness of the lease inventory. The Company determined that most of the current operating leases were subject to the guidance and were recognized as operating lease liabilities and right-of-use assets on the Consolidated Balance Sheet upon adoption. On January 1, 2019, the Company recorded approximately $112 million to right-of-use assets and lease liabilities as a result of the initial adoption of the guidance. In addition, the Company evaluated the impact the new guidance had on lease contracts where the Company is the lessor and determined it did not have a significant impact to the Company's financial statements. ASU 2018-15 - Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract In August 2018, the FASB issued guidance on the accounting for implementation costs of a hosting arrangement that is a service contract. The guidance aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract similar to the costs incurred to develop or obtain internal-use software and such capitalized costs to be expensed over the term of the hosting arrangement. Costs incurred during the preliminary and postimplementation stages should continue to be expensed as activities are performed. The capitalized costs are required to be presented on the balance sheet in the same line the prepayment for the fees associated with the hosting arrangement would be presented. In addition, the expense related to the capitalized implementation costs should be presented in the same line on the income statement as the fees associated with the hosting element of the arrangements. The Company adopted the guidance effective January 1, 2019, on a prospective basis. The adoption of the guidance did not have a material impact on its results of operations, financial position, cash flows or disclosures. Recently issued accounting standards not yet adopted ASU 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 introduces a new impairment model known as the current expected credit loss model that will replace the incurred loss impairment methodology currently included under GAAP. This guidance requires 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 guidance will be effective for the Company on January 1, 2020, and must be applied on a modified retrospective basis with early adoption permitted. The Company continues to evaluate the provisions of the guidance and currently does not expect the guidance to have a material impact on its results of operations, financial position, cash flows or disclosures. ASU 2017-04 - Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued guidance on simplifying the test for goodwill impairment by eliminating Step 2, which required an entity to measure the amount of impairment loss by comparing the implied fair value of reporting unit goodwill with the carrying amount of such goodwill. This guidance requires entities to perform a quantitative impairment test, previously Step 1, to identify both the existence of impairment and the amount of impairment loss by comparing the fair value of a reporting unit to its carrying amount. Entities will continue to have the option of performing a qualitative assessment to determine if the quantitative impairment test is necessary. The guidance also requires additional disclosures if an entity has one or more reporting units with zero or negative carrying amounts of net assets. The guidance will be effective for the Company on January 1, 2020, and must be applied on a prospective basis with early adoption permitted. The Company has evaluated the guidance and does not expect the guidance will have a material impact on its results of operations, financial position, cash flows or disclosures upon adoption. The Company is planning to early adopt the guidance with the preparation of its 2019 goodwill impairment test in the fourth quarter of 2019. 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 modifies, among other things, the disclosures required for Level 3 fair value measurements, including the range and weighted average of significant unobservable inputs. The guidance removes, among other things, the disclosure requirement to disclose transfers between Levels 1 and 2. The guidance will be effective for the Company on January 1, 2020, including interim periods, with early adoption permitted. Level 3 fair value measurement disclosures should be applied prospectively while all other amendments should be applied retrospectively. The Company is evaluating the effects the adoption of the new guidance will have on its disclosures. 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.

Revenue from contracts with c_2

Revenue from contracts with customers (Policies)	9 Months Ended
	Sep. 30, 2019
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, 2019
Business Combinations [Abstract]
Business Combinations Policy [Policy Text Block]	All business combinations were accounted for in accordance with ASC 805 - Business Combinations . The results of the acquired businesses have been included in the Company's Consolidated Financial Statements beginning on the acquisition date. Pro forma financial amounts reflecting the effects of the business combinations are not presented, as these business combinations were not 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, estimated fair value of 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 2019 and 2018 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 one year 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.

Discontinued operations (Polici

Discontinued operations (Policies)	9 Months Ended
	Sep. 30, 2019
Discontinued Operations and Disposal Groups [Abstract]
Discontinued operations	The assets and liabilities of the Company's discontinued operations have been classified as held for sale and the results of operations are shown in income (loss) from discontinued operations, other than certain general and administrative costs and interest expense which do not meet the criteria for income (loss) from discontinued operations. At the time the assets were classified as held for sale, depreciation, depletion and amortization expense was no longer recorded.

Leases (Policies)

Leases (Policies)	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Lessee, Leases [Policy Text Block]	The leases the Company has entered into as part of its ongoing operations are considered operating leases and are recognized on the balance sheet as right-of-use assets, current lease liabilities and, if applicable, noncurrent lease liabilities. Lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The Company determines the lease term based on the non-cancelable and cancelable periods in each contract. The non-cancelable period consists of the term of the contract that is legally enforceable and cannot be canceled by either party without incurring a significant penalty. The cancelable period is determined by various factors that are based on who has the right to cancel a contract. If only the lessor has the right to cancel the contract, the Company will assume the contract will continue. If the lessee is the only party that has the right to cancel the contract, the Company looks to asset, entity and market-based factors. If both the lessor and the lessee have the right to cancel the contract, the Company assumes the contract will not continue.

Fair value disclosures (Policie

Fair value disclosures (Policies)	9 Months Ended
	Sep. 30, 2019
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. The available-for-sale securities 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, 2019
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, 2019
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.

Inventories and natural gas i_3

Inventories and natural gas in storage (Tables)	9 Months Ended
	Sep. 30, 2019
Inventory Disclosure [Abstract]
Inventories	Inventories on the Consolidated Balance Sheets were as follows: September 30, 2019 September 30, 2018 December 31, 2018 (In thousands) Aggregates held for resale $ 143,157 $ 133,477 $ 139,681 Asphalt oil 39,269 40,781 54,741 Materials and supplies 25,696 23,563 23,611 Merchandise for resale 23,902 15,954 22,552 Natural gas in storage (current) 32,164 29,084 22,117 Other 21,869 27,434 24,607 Total $ 286,057 $ 270,293 $ 287,309

Earnings per common share (Tabl

Earnings per common share (Tables)	9 Months Ended
	Sep. 30, 2019
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, 2019 2018 2019 2018 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 199,343 196,018 198,016 195,618 Effect of dilutive performance share awards and restricted stock units 40 247 17 486 Weighted average common shares outstanding - diluted 199,383 196,265 198,033 196,104 Shares excluded from the calculation of diluted earnings per share 155 114 243 — Dividends declared per common share $ .2025 $ .1975 $ .6075 $ .5925

Accumulated other comprehensi_2

Accumulated other comprehensive income (loss) (Tables)	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Accumulated comprehensive loss	The after-tax changes in the components of accumulated other comprehensive income (loss) were as follows: Nine Months Ended September 30, 2019 Net Unrealized Gain (Loss) on Derivative 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 ) Nine Months Ended September 30, 2018 Net Unrealized Gain (Loss) on Derivative Postretirement Foreign Net Unrealized Total (In thousands) At December 31, 2017 $ (1,934 ) $ (35,163 ) $ (155 ) $ (82 ) $ (37,334 ) Other comprehensive loss before reclassifications — — (2 ) (105 ) (107 ) Amounts reclassified from accumulated other comprehensive loss 92 418 — 30 540 Net current-period other comprehensive income (loss) 92 418 (2 ) (75 ) 433 Reclassification adjustment of prior period tax effects related to TCJA included in accumulated other comprehensive loss (389 ) (7,520 ) (33 ) (17 ) (7,959 ) At March 31, 2018 $ (2,231 ) $ (42,265 ) $ (190 ) $ (174 ) $ (44,860 ) Other comprehensive loss before reclassifications — — (59 ) (43 ) (102 ) Amounts reclassified from accumulated other comprehensive loss 95 449 249 34 827 Net current-period other comprehensive income (loss) 95 449 190 (9 ) 725 At June 30, 2018 $ (2,136 ) $ (41,816 ) $ — $ (183 ) $ (44,135 ) Other comprehensive loss before reclassifications — — — (51 ) (51 ) Amounts reclassified from accumulated other comprehensive loss 92 442 — 33 567 Net current-period other comprehensive income (loss) 92 442 — (18 ) 516 At September 30, 2018 $ (2,044 ) $ (41,374 ) $ — $ (201 ) $ (43,619 )
Reclassification out of accumulated other comprehensive loss	The following amounts were reclassified out of accumulated other comprehensive loss into net income. The amounts presented in parenthesis indicate a decrease to net income on the Consolidated Statements of Income. The reclassifications were as follows: Three Months Ended Nine Months Ended Location on Consolidated Statements of Income September 30, September 30, 2019 2018 2019 2018 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ (148 ) $ (147 ) $ (443 ) $ (443 ) Interest expense 36 55 (177 ) 164 Income taxes (112 ) (92 ) (620 ) (279 ) Amortization of postretirement liability losses included in net periodic benefit cost (387 ) (584 ) (1,162 ) (1,751 ) Other income 95 142 284 442 Income taxes (292 ) (442 ) (878 ) (1,309 ) Reclassification adjustment for foreign currency translation adjustment included in net income — — — (324 ) Other income — — — 75 Income taxes — — — (249 ) Reclassification adjustment on available-for-sale investments included in net income 5 (42 ) (46 ) (123 ) Other income (1 ) 9 10 26 Income taxes 4 (33 ) (36 ) (97 ) Total reclassifications $ (400 ) $ (567 ) $ (1,534 ) $ (1,934 )

Revenue from contracts with c_3

Revenue from contracts with customers (Tables)	9 Months Ended
	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of revenue	In the following table, revenue is disaggregated by the type of customer or service provided. The Company believes this level of disaggregation best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The table also includes a reconciliation of the disaggregated revenue by reportable segments. For more information on the Company's business segments, see Note 17 . Three Months Ended September 30, 2019 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services 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 * Intrasegment revenues are presented 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. Three Months Ended September 30, 2018 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 31,424 $ 43,825 $ — $ — $ — $ — $ 75,249 Commercial utility sales 36,259 28,174 — — — — 64,433 Industrial utility sales 8,738 4,421 — — — — 13,159 Other utility sales 2,056 — — — — — 2,056 Natural gas transportation — 10,841 21,400 — — — 32,241 Natural gas gathering — — 2,320 — — — 2,320 Natural gas storage — — 2,795 — — — 2,795 Contracting services — — — 409,006 — — 409,006 Construction materials — — — 538,962 — — 538,962 Intrasegment eliminations* — — — (204,040 ) — — (204,040 ) Inside specialty contracting — — — — 217,474 — 217,474 Outside specialty contracting — — — — 100,988 — 100,988 Other 6,158 3,208 5,701 — 15 3,084 18,166 Intersegment eliminations — — (3,187 ) (165 ) (782 ) (3,037 ) (7,171 ) Revenues from contracts with customers 84,635 90,469 29,029 743,763 317,695 47 1,265,638 Revenues out of scope 1,445 1,779 42 — 11,883 — 15,149 Total external operating revenues $ 86,080 $ 92,248 $ 29,071 $ 743,763 $ 329,578 $ 47 $ 1,280,787 * Intrasegment revenues are presented 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. Nine Months Ended September 30, 2019 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services 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 * Intrasegment revenues are presented 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. Nine Months Ended September 30, 2018 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 93,359 $ 305,399 $ — $ — $ — $ — $ 398,758 Commercial utility sales 103,636 185,885 — — — — 289,521 Industrial utility sales 25,734 17,457 — — — — 43,191 Other utility sales 5,766 — — — — — 5,766 Natural gas transportation — 32,104 64,505 — — — 96,609 Natural gas gathering — — 6,900 — — — 6,900 Natural gas storage — — 8,563 — — — 8,563 Contracting services — — — 730,628 — — 730,628 Construction materials — — — 1,100,185 — — 1,100,185 Intrasegment eliminations* — — — (363,877 ) — — (363,877 ) Inside specialty contracting — — — — 667,664 — 667,664 Outside specialty contracting — — — — 283,432 — 283,432 Other 22,836 10,821 13,353 — 32 8,536 55,578 Intersegment eliminations — — (31,485 ) (501 ) (1,332 ) (8,343 ) (41,661 ) Revenues from contracts with customers 251,331 551,666 61,836 1,466,435 949,796 193 3,281,257 Revenues out of scope 653 2,786 129 — 36,853 — 40,421 Total external operating revenues $ 251,984 $ 554,452 $ 61,965 $ 1,466,435 $ 986,649 $ 193 $ 3,321,678 * Intrasegment revenues are presented 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 changes in contract assets and liabilities were as follows: September 30, 2019 December 31, 2018 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 163,437 $ 104,239 $ 59,198 Receivables, net Contract liabilities - current (120,207 ) (93,901 ) (26,306 ) Accounts payable Contract liabilities - noncurrent (25 ) (135 ) 110 Deferred credits and other liabilities - other Net contract assets $ 43,205 $ 10,203 $ 33,002

Business Combinations Business

Business Combinations Business Combinations (Tables)	9 Months Ended
	Sep. 30, 2019
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition [Table Text Block]	The aggregate total consideration for the 2018 acquisitions and the final amounts allocated to the assets acquired and liabilities assumed were as follows: December 31, 2018 Measurement Period Adjustments September 30, 2019 (In thousands) Assets Current assets: Receivables, net $ 18,984 $ — $ 18,984 Inventories 10,329 (228 ) 10,101 Prepayments and other current assets 515 (14 ) 501 Total current assets 29,828 (242 ) 29,586 Property, plant and equipment 131,766 6,669 138,435 Deferred charges and other assets: Goodwill 33,131 (6,669 ) 26,462 Other Intangible assets, net 8,227 — 8,227 Other 927 — 927 Total deferred charges and other assets 42,285 (6,669 ) 35,616 Total assets acquired $ 203,879 $ (242 ) $ 203,637 Liabilities Current liabilities $ 11,122 $ (242 ) $ 10,880 Deferred credits and other liabilities: Asset retirement obligation 914 — 914 Deferred income taxes 5,565 — 5,565 Total deferred credits and other liabilities 6,479 — 6,479 Total liabilities assumed $ 17,601 $ (242 ) $ 17,359 Total consideration (fair value) $ 186,278 $ — $ 186,278

Discontinued operations (Tables

Discontinued operations (Tables)	9 Months Ended
	Sep. 30, 2019
Discontinued Operations and Disposal Groups [Abstract]
Disposal groups, including discontinued operations	The carrying amounts of the major classes of assets and liabilities classified as held for sale on the Consolidated Balance Sheets were as follows: September 30, 2019 September 30, 2018 December 31, 2018 (In thousands) Assets Current assets: Receivables, net $ 426 $ 571 $ 430 Income taxes receivable (a) — 1,640 — Total current assets held for sale 426 2,211 430 Noncurrent assets: Deferred income taxes 1,926 1,711 1,926 Other 161 161 161 Total noncurrent assets held for sale 2,087 1,872 2,087 Total assets held for sale $ 2,513 $ 4,083 $ 2,517 Liabilities Current liabilities: Accounts payable $ — $ 188 $ 80 Taxes payable 1,300 7,463 1,451 Other accrued liabilities 2,093 1,948 2,470 Total current liabilities held for sale 3,393 9,599 4,001 Noncurrent liabilities: Deferred income taxes (b) — 37 — Total noncurrent liabilities held for sale — 37 — Total liabilities held for sale $ 3,393 $ 9,636 $ 4,001 (a) On the Company's Consolidated Balance Sheets, these amounts were reclassified to taxes payable and are reflected in current liabilities held for sale. (b) On the Company's Consolidated Balance Sheets, these amounts were reclassified to deferred charges and other assets - deferred income taxes and are reflected in noncurrent assets held for sale.
Reconciliation of major classes of income and expense	The reconciliation of the major classes of income and expense constituting pretax income (loss) from discontinued operations to the after-tax income (loss) from discontinued operations on the Consolidated Statements of Income was as follows: Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 (In thousands) Operating revenues $ 230 $ 61 $ 298 $ 201 Operating expenses (1,760 ) 216 264 825 Operating income (loss) 1,990 (155 ) 34 (624 ) Other income — — — 12 Interest expense — — — 575 Income (loss) from discontinued operations before income taxes 1,990 (155 ) 34 (1,187 ) Income taxes 481 (37 ) 8 (1,272 ) Income (loss) from discontinued operations $ 1,509 $ (118 ) $ 26 $ 85

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Lease, Cost [Table Text Block]	The following tables provide information on the Company's operating leases: Three Months Ended Nine Months Ended September 30, September 30, 2019 2019 (In thousands) Lease costs: Operating lease cost $ 10,536 $ 32,444 Variable lease cost 381 1,180 Short-term lease cost 28,270 85,982 Total lease costs $ 39,187 $ 119,606 September 30, 2019 (Dollars in thousands) Weighted average remaining lease term 2.98 years Weighted average discount rate 4.63 % Cash paid for amounts included in the measurement of lease liabilities $ 32,261
Lessee, Operating Lease, Liability, Maturity [Table Text Block]	The reconciliation of the future undiscounted cash flows to the operating lease liabilities presented on the Company's Consolidated Balance Sheet at September 30, 2019 , was as follows: (In thousands) Remainder of 2019 $ 10,619 2020 32,605 2021 23,488 2022 15,838 2023 9,913 Thereafter 54,765 Total 147,228 Less discount 28,478 Total operating lease liabilities $ 118,750 As previously disclosed in the 2018 Annual Report, the undiscounted annual minimum lease payments due under the Company's leases following the previous lease accounting standard as of December 31, 2018, were as follows: 2019 2020 2021 2022 2023 Thereafter (In thousands) Operating leases $ 37,740 $ 26,255 $ 17,868 $ 11,647 $ 7,278 $ 49,098

Goodwill and other intangible_2

Goodwill and other intangible assets (Tables)	9 Months Ended
	Sep. 30, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the carrying amount of goodwill	The changes in the carrying amount of goodwill were as follows: Nine Months Ended September 30, 2019 Balance at January 1, 2019 Goodwill Acquired the Year Measurement Period Adjustments 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 Nine Months Ended September 30, 2018 Balance at January 1, 2018 Goodwill Acquired the Year Measurement Period Adjustments Balance at September 30, 2018 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 176,290 8,412 — 184,702 Construction services 109,765 — — 109,765 Total $ 631,791 $ 8,412 $ — $ 640,203 Year Ended December 31, 2018 Balance at January 1, 2018 Goodwill Acquired the Year Measurement Period Adjustments Balance at December 31, 2018 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Construction materials and contracting 176,290 33,131 — 209,421 Construction services 109,765 — — 109,765 Total $ 631,791 $ 33,131 $ — $ 664,922
Other amortizable intangible assets	Other amortizable intangible assets were as follows: September 30, 2019 September 30, 2018 December 31, 2018 (In thousands) Customer relationships $ 18,011 $ 15,920 $ 22,720 Less accumulated amortization 5,823 13,342 13,535 12,188 2,578 9,185 Noncompete agreements 3,419 2,606 2,605 Less accumulated amortization 1,868 1,911 1,956 1,551 695 649 Other 7,488 6,458 6,458 Less accumulated amortization 5,716 5,413 5,477 1,772 1,045 981 Total $ 15,511 $ 4,318 $ 10,815
Estimated amortization expense	Estimated amortization expense for identifiable intangible assets as of September 30, 2019 , was: Remainder of 2019 2020 2021 2022 2023 Thereafter (In thousands) Amortization expense $ 931 $ 3,077 $ 2,042 $ 1,996 $ 1,957 $ 5,508

Regulatory assets and liabili_2

Regulatory assets and liabilities (Tables)	9 Months Ended
	Sep. 30, 2019
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	The following table summarizes the individual components of unamortized regulatory assets and liabilities: Estimated Recovery Period * September 30, 2019 December 31, 2018 (In thousands) Regulatory assets: Pension and postretirement benefits (a) (e) $ 165,843 $ 165,898 Natural gas costs recoverable through rate adjustments (a) (b) Up to 3 years 93,001 42,652 Asset retirement obligations (a) Over plant lives 64,771 60,097 Cost recovery mechanisms (a) (b) Up to 4 years 20,912 17,948 Manufactured gas plant site remediation (a) - 15,739 17,068 Taxes recoverable from customers (a) Over plant lives 11,600 11,946 Plants to be retired (a) - 26,152 — Conservation programs (b) Up to 1 year 9,467 7,494 Long-term debt refinancing costs (a) Up to 19 years 4,439 4,898 Costs related to identifying generation development (a) Up to 8 years 2,166 2,508 Other (a) (b) Up to 20 years 17,501 9,608 Total regulatory assets $ 431,591 $ 340,117 Regulatory liabilities: Taxes refundable to customers (c) (d) $ 258,012 $ 277,833 Plant removal and decommissioning costs (c) (d) 176,016 173,143 Natural gas costs refundable through rate adjustments (d) 19,194 29,995 Pension and postretirement benefits (c) 12,942 15,264 Other (c) (d) 24,153 25,197 Total regulatory liabilities $ 490,317 $ 521,432 Net regulatory position $ (58,726 ) $ (181,315 ) * Estimated recovery period for regulatory assets currently being recovered in rates charged to customers. (a) Included in deferred charges and other assets - other on the Consolidated Balance Sheets. (b) Included in prepayments and other current assets on the Consolidated Balance Sheets. (c) Included in deferred credits and other liabilities - other on the Consolidated Balance Sheets. (d) Included in other accrued liabilities on the Consolidated Balance Sheets. (e) Recovered as expense is incurred or cash contributions are made.
Regulatory Liabilities	The following table summarizes the individual components of unamortized regulatory assets and liabilities: Estimated Recovery Period * September 30, 2019 December 31, 2018 (In thousands) Regulatory assets: Pension and postretirement benefits (a) (e) $ 165,843 $ 165,898 Natural gas costs recoverable through rate adjustments (a) (b) Up to 3 years 93,001 42,652 Asset retirement obligations (a) Over plant lives 64,771 60,097 Cost recovery mechanisms (a) (b) Up to 4 years 20,912 17,948 Manufactured gas plant site remediation (a) - 15,739 17,068 Taxes recoverable from customers (a) Over plant lives 11,600 11,946 Plants to be retired (a) - 26,152 — Conservation programs (b) Up to 1 year 9,467 7,494 Long-term debt refinancing costs (a) Up to 19 years 4,439 4,898 Costs related to identifying generation development (a) Up to 8 years 2,166 2,508 Other (a) (b) Up to 20 years 17,501 9,608 Total regulatory assets $ 431,591 $ 340,117 Regulatory liabilities: Taxes refundable to customers (c) (d) $ 258,012 $ 277,833 Plant removal and decommissioning costs (c) (d) 176,016 173,143 Natural gas costs refundable through rate adjustments (d) 19,194 29,995 Pension and postretirement benefits (c) 12,942 15,264 Other (c) (d) 24,153 25,197 Total regulatory liabilities $ 490,317 $ 521,432 Net regulatory position $ (58,726 ) $ (181,315 ) * Estimated recovery period for regulatory assets currently being recovered in rates charged to customers. (a) Included in deferred charges and other assets - other on the Consolidated Balance Sheets. (b) Included in prepayments and other current assets on the Consolidated Balance Sheets. (c) Included in deferred credits and other liabilities - other on the Consolidated Balance Sheets. (d) Included in other accrued liabilities on the Consolidated Balance Sheets. (e) Recovered as expense is incurred or cash contributions are made.

Fair value measurements (Tables

Fair value measurements (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Available-for-sale securities	Details of available-for-sale securities were as follows: September 30, 2019 Cost Gross Unrealized Gains Gross Unrealized Losses 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 September 30, 2018 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,550 $ 3 $ 251 $ 10,302 U.S. Treasury securities 179 — — 179 Total $ 10,729 $ 3 $ 251 $ 10,481 December 31, 2018 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,473 $ 21 $ 162 $ 10,332 U.S. Treasury securities 179 — — 179 Total $ 10,652 $ 21 $ 162 $ 10,511
Assets and liabilities measured at fair value on a recurring basis	The Company's assets and liabilities measured at fair value on a recurring basis were as follows: Fair Value Measurements at September 30, 2019, Using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) 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 September 30, 2018, Using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Balance at September 30, 2018 (In thousands) Assets: Money market funds $ — $ 9,948 $ — $ 9,948 Insurance contract* — 80,358 — 80,358 Available-for-sale securities: Mortgage-backed securities — 10,302 — 10,302 U.S. Treasury securities — 179 — 179 Total assets measured at fair value $ — $ 100,787 $ — $ 100,787 * The insurance contract invests approximately 47 percent in fixed-income investments, 24 percent in common stock of large-cap companies, 13 percent in common stock of mid-cap companies, 12 percent in common stock of small-cap companies, 3 percent in target date investments and 1 percent in cash equivalents. Fair Value Measurements at December 31, 2018, Using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Balance at December 31, 2018 (In thousands) Assets: Money market funds $ — $ 10,799 $ — $ 10,799 Insurance contract* — 73,838 — 73,838 Available-for-sale securities: Mortgage-backed securities — 10,332 — 10,332 U.S. Treasury securities — 179 — 179 Total assets measured at fair value $ — $ 95,148 $ — $ 95,148 * 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 of long term debt outstanding	The estimated fair value of the Company's long-term debt was as follows: Carrying Amount Fair Value (In thousands) Long-term debt at September 30, 2019 $ 2,246,756 $ 2,450,209 Long-term debt at September 30, 2018 $ 1,915,470 $ 1,987,360 Long-term debt at December 31, 2018 $ 2,108,695 $ 2,183,819

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Long-term debt outstanding	Long-term debt outstanding was as follows: Weighted Average Interest Rate at September 30, 2019 September 30, 2019 December 31, 2018 (In thousands) Senior notes due on dates ranging from December 15, 2019 to January 15, 2055 4.52 % $ 1,655,000 $ 1,381,000 Commercial paper supported by revolving credit agreements 2.46 % 281,800 338,100 Term loan agreements due on dates ranging from September 3, 2032 to November 18, 2059 2.75 % 209,100 209,800 Credit agreements due on June 7, 2024 4.66 % 31,000 110,100 Medium-term notes due on dates ranging from September 1, 2020 to March 16, 2029 6.68 % 50,000 50,000 Other notes due on dates ranging from July 15, 2021 to November 30, 2038 5.01 % 26,083 25,229 Less unamortized debt issuance costs 6,074 5,207 Less discount 153 327 Total long-term debt 2,246,756 2,108,695 Less current maturities 65,810 251,854 Net long-term debt $ 2,180,946 $ 1,856,841
Schedule of debt maturities	Long-term debt maturities, which excludes unamortized debt issuance costs and discount, as of September 30, 2019 , were as follows: Remainder of 2019 2020 2021 2022 2023 Thereafter (In thousands) Long-term debt maturities $ 50,110 $ 15,902 $ 204,522 $ 147,402 $ 155,502 $ 1,679,545

Cash flow information (Tables)

Cash flow information (Tables)	9 Months Ended
	Sep. 30, 2019
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, 2019 2018 (In thousands) Interest, net* $ 64,596 $ 58,359 Income taxes paid, net** $ 1,816 $ 8,887 * AFUDC - borrowed was $2.0 million and $1.8 million for the nine months ended September 30, 2019 and 2018 , respectively. ** Income taxes paid, including discontinued operations, were $2.0 million and $5.1 million for the nine months ended September 30, 2019 and 2018 , respectively. Noncash investing and financing transactions were as follows: September 30, 2019 September 30, 2018 December 31, 2018 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 46,770 $ — $ — Property, plant and equipment additions in accounts payable $ 34,368 $ 34,594 $ 42,355 Debt assumed in connection with a business combination $ 1,163 $ — $ — Issuance of common stock in connection with a business combination $ — $ 17,993 $ 18,186

Business segment data (Tables)

Business segment data (Tables)	9 Months Ended
	Sep. 30, 2019
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, 2019 2018 2019 2018 (In thousands) External operating revenues: Regulated operations: Electric $ 89,845 $ 86,080 $ 263,423 $ 251,984 Natural gas distribution 93,642 92,248 569,656 554,452 Pipeline and midstream 25,957 22,289 52,230 45,325 209,444 200,617 885,309 851,761 Nonregulated operations: Pipeline and midstream 6,576 6,782 17,597 16,640 Construction materials and contracting 869,376 743,763 1,692,287 1,466,435 Construction services 478,381 329,578 1,363,305 986,649 Other 22 47 65 193 1,354,355 1,080,170 3,073,254 2,469,917 Total external operating revenues $ 1,563,799 $ 1,280,787 $ 3,958,563 $ 3,321,678 Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 (In thousands) Intersegment operating revenues: Regulated operations: Electric $ — $ — $ — $ — Natural gas distribution — — — — Pipeline and midstream 3,750 3,070 35,098 31,252 3,750 3,070 35,098 31,252 Nonregulated operations: Pipeline and midstream 81 117 200 233 Construction materials and contracting 124 165 388 501 Construction services 1,226 782 2,076 1,332 Other 2,862 3,037 13,566 8,343 4,293 4,101 16,230 10,409 Intersegment eliminations (8,043 ) (7,171 ) (51,328 ) (41,661 ) Total intersegment operating revenues $ — $ — $ — $ — Operating income (loss): Electric $ 21,930 $ 21,140 $ 49,708 $ 52,321 Natural gas distribution (15,565 ) (11,665 ) 32,132 32,503 Pipeline and midstream 11,416 9,036 32,017 25,687 Construction materials and contracting 143,024 109,598 147,622 120,591 Construction services 29,950 11,863 89,381 51,853 Other (1,285 ) 32 140 417 Total operating income $ 189,470 $ 140,004 $ 351,000 $ 283,372 Net income (loss): Regulated operations: Electric $ 16,291 $ 15,284 $ 39,267 $ 37,500 Natural gas distribution (15,625 ) (11,887 ) 14,623 13,884 Pipeline and midstream 6,933 10,109 20,316 20,809 7,599 13,506 74,206 72,193 Nonregulated operations: Pipeline and midstream 801 848 1,380 1,136 Construction materials and contracting 102,611 78,876 97,328 79,691 Construction services 21,113 9,278 63,982 38,457 Other 4,004 4,861 3,466 1,928 128,529 93,863 166,156 121,212 Income from continuing operations 136,128 107,369 240,362 193,405 Income (loss) from discontinued operations, net of tax 1,509 (118 ) 26 85 Net income $ 137,637 $ 107,251 $ 240,388 $ 193,490

Employee benefit plans (Tables)

Employee benefit plans (Tables)	9 Months Ended
	Sep. 30, 2019
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 Postretirement Benefits Three Months Ended September 30, 2019 2018 2019 2018 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 286 $ 374 Interest cost 3,806 3,648 746 725 Expected return on assets (4,559 ) (5,188 ) (1,201 ) (1,217 ) Amortization of prior service credit — — (289 ) (349 ) Amortization of net actuarial loss 1,387 1,751 27 160 Net periodic benefit cost (credit), including amount capitalized 634 211 (431 ) (307 ) Less amount capitalized — — 26 46 Net periodic benefit cost (credit) $ 634 $ 211 $ (457 ) $ (353 ) Pension Benefits Other Postretirement Benefits Nine Months Ended September 30, 2019 2018 2019 2018 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 857 $ 1,121 Interest cost 11,419 10,943 2,239 2,175 Expected return on assets (13,677 ) (15,565 ) (3,603 ) (3,650 ) Amortization of prior service credit — — (866 ) (1,046 ) Amortization of net actuarial loss 4,160 5,254 82 480 Net periodic benefit cost (credit), including amount capitalized 1,902 632 (1,291 ) (920 ) Less amount capitalized — — 84 128 Net periodic benefit cost (credit) $ 1,902 $ 632 $ (1,375 ) $ (1,048 )

Accounts receivable and allow_3

Accounts receivable and allowance for doubtful accounts (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Receivables [Abstract]
Receivables past due 90 days or more	$ 56	$ 30	$ 29.2
Allowance for doubtful accounts receivable	$ 8.7	$ 8.9	$ 7.3

Inventories and natural gas i_4

Inventories and natural gas in storage (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Inventory Disclosure [Abstract]
Aggregates held for resale	$ 143,157	$ 139,681	$ 133,477
Asphalt oil	39,269	54,741	40,781
Materials and supplies	25,696	23,611	23,563
Merchandise for resale	23,902	22,552	15,954
Natural gas in storage (current)	32,164	22,117	29,084
Other	21,869	24,607	27,434
Total	286,057	287,309	270,293
Natural gas in storage noncurrent	$ 48,200	$ 48,500	$ 47,800

Earnings per common share (Deta

Earnings per common share (Details) - $ / shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	199,343	196,018	198,016	195,618
Effect of dilutive performance share awards and restricted stock units	40	247	17	486
Weighted average common shares outstanding - diluted	199,383	196,265	198,033	196,104
Shares excluded from the calculation of diluted earnings per share	155	114	243	0
Dividends declared per common share	$ 0.2025	$ 0.1975	$ 0.6075	$ 0.5925

New accounting standards ASU 20

New accounting standards ASU 2016-02 (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 112

Accumulated other comprehensi_3

Accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	$ 2,660,301	$ 2,605,692	$ 2,566,775	$ 2,451,078	$ 2,426,111	$ 2,429,043	$ 2,566,775	$ 2,429,043
Other comprehensive income	412	478	774	516	725	433	1,664	1,674
Balance	2,795,606	2,660,301	2,605,692	2,521,293	2,451,078	2,426,111	2,795,606	2,521,293
Net unrealized gain (loss) on derivative instruments qualifying as hedges
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(1,653)	(1,764)	(2,161)	(2,136)	(2,231)	(1,934)	(2,161)	(1,934)
Other comprehensive income before reclassifications	0	0	0	0	0	0
Amounts reclassified (to) from accumulated other comprehensive loss	112	111	397	92	95	92
Other comprehensive income	112	111	397	92	95	92
Balance	(1,541)	(1,653)	(1,764)	(2,044)	(2,136)	(2,231)	(1,541)	(2,044)
Postretirement liability adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(35,483)	(35,759)	(36,069)	(41,816)	(42,265)	(35,163)	(36,069)	(35,163)
Other comprehensive income before reclassifications	0	0	0	0	0	0
Amounts reclassified (to) from accumulated other comprehensive loss	292	276	310	442	449	418
Other comprehensive income	292	276	310	442	449	418
Balance	(35,191)	(35,483)	(35,759)	(41,374)	(41,816)	(42,265)	(35,191)	(41,374)
Foreign currency translation adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Balance				0	(190)	(155)		(155)
Other comprehensive income before reclassifications				0	(59)	(2)
Amounts reclassified (to) from accumulated other comprehensive loss				0	249	0
Other comprehensive income				0	190	(2)
Balance				0	0	(190)		0
Net unrealized gain (loss) on available-for-sale investments
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	46	(45)	(112)	(183)	(174)	(82)	(112)	(82)
Other comprehensive income before reclassifications	12	79	39	(51)	(43)	(105)
Amounts reclassified (to) from accumulated other comprehensive loss	(4)	12	28	33	34	30
Other comprehensive income	8	91	67	(18)	(9)	(75)
Balance	54	46	(45)	(201)	(183)	(174)	54	(201)
Total accumulated other comprehensive loss
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(37,090)	(37,568)	(38,342)	(44,135)	(44,860)	(37,334)	(38,342)	(37,334)
Other comprehensive income before reclassifications	12	79	39	(51)	(102)	(107)
Amounts reclassified (to) from accumulated other comprehensive loss	400	399	735	567	827	540
Other comprehensive income	412	478	774	516	725	433
Balance	$ (36,678)	$ (37,090)	$ (37,568)	$ (43,619)	$ (44,135)	(44,860)	$ (36,678)	$ (43,619)
Tax Cuts and Jobs Act [Member] | Adjustments for New Accounting Principle, Early Adoption [Member] | Net unrealized gain (loss) on derivative instruments qualifying as hedges
Accumulated other comprehensive income (loss) [Roll Forward]
Reclassification adjustment of prior period tax effects related to TCJA included in accumulated other comprehensive loss						(389)
Tax Cuts and Jobs Act [Member] | Adjustments for New Accounting Principle, Early Adoption [Member] | Postretirement liability adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Reclassification adjustment of prior period tax effects related to TCJA included in accumulated other comprehensive loss						(7,520)
Tax Cuts and Jobs Act [Member] | Adjustments for New Accounting Principle, Early Adoption [Member] | Foreign currency translation adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Reclassification adjustment of prior period tax effects related to TCJA included in accumulated other comprehensive loss						(33)
Tax Cuts and Jobs Act [Member] | Adjustments for New Accounting Principle, Early Adoption [Member] | Net unrealized gain (loss) on available-for-sale investments
Accumulated other comprehensive income (loss) [Roll Forward]
Reclassification adjustment of prior period tax effects related to TCJA included in accumulated other comprehensive loss						(17)
Tax Cuts and Jobs Act [Member] | Adjustments for New Accounting Principle, Early Adoption [Member] | Total accumulated other comprehensive loss
Accumulated other comprehensive income (loss) [Roll Forward]
Reclassification adjustment of prior period tax effects related to TCJA included in accumulated other comprehensive loss						$ (7,959)

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, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Interest expense	$ (25,258)			$ (20,955)			$ (74,094)	$ (62,202)
Income taxes	(31,098)			(14,363)			(48,766)	(32,629)
Other income	3,014			2,683			12,222	4,864
Net Income	137,637	$ 61,825	$ 40,926	107,251	$ 43,802	$ 42,437	240,388	193,490
Reclassification out of accumulated other comprehensive income
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Net Income	(400)			(567)			(1,534)	(1,934)
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)			(147)			(443)	(443)
Income taxes	36			55			(177)	164
Net Income	(112)			(92)			(620)	(279)
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	95			142			284	442
Other income	(387)			(584)			(1,162)	(1,751)
Net Income	(292)			(442)			(878)	(1,309)
Reclassification adjustment for foreign currency translation adjustment included in net income | Reclassification out of accumulated other comprehensive income
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Income taxes	0			0			0	75
Other income	0			0			0	(324)
Net Income	0			0			0	(249)
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	(1)			9			10	26
Other income	5			(42)			(46)	(123)
Net Income	$ 4			$ (33)			$ (36)	$ (97)

Disaggregation of revenue (Deta

Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 1,563,799	$ 1,280,787	$ 3,958,563	$ 3,321,678
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(8,043)	(7,171)	(51,328)	(41,661)
Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(231,078)	(204,040)	(412,144)	(363,877)
Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues	36,639	32,241	108,777	96,609
Natural gas gathering
Disaggregation of Revenue [Line Items]
Revenues	2,510	2,320	7,027	6,900
Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues	3,044	2,795	8,313	8,563
Contracting services
Disaggregation of Revenue [Line Items]
Revenues	461,716	409,006	841,881	730,628
Construction materials
Disaggregation of Revenue [Line Items]
Revenues	638,862	538,962	1,262,938	1,100,185
Inside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	317,202	217,474	936,008	667,664
Outside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	151,285	100,988	391,971	283,432
Other
Disaggregation of Revenue [Line Items]
Revenues	20,551	18,166	64,686	55,578
Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	1,549,301	1,265,638	3,917,392	3,281,257
Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	14,498	15,149	41,171	40,421
Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	75,278	75,249	409,889	398,758
Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	65,818	64,433	297,763	289,521
Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	13,655	13,159	46,071	43,191
Other utility sales
Disaggregation of Revenue [Line Items]
Revenues	1,862	2,056	5,540	5,766
Electric
Disaggregation of Revenue [Line Items]
Revenues	89,845	86,080	263,423	251,984
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	9,380	6,158	26,918	22,836
Electric | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	87,636	84,635	258,974	251,331
Electric | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	2,209	1,445	4,449	653
Electric | Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	30,376	31,424	93,368	93,359
Electric | Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	36,670	36,259	105,572	103,636
Electric | Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	9,348	8,738	27,576	25,734
Electric | Other utility sales
Disaggregation of Revenue [Line Items]
Revenues	1,862	2,056	5,540	5,766
Natural gas distribution
Disaggregation of Revenue [Line Items]
Revenues	93,642	92,248	569,656	554,452
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Natural gas distribution | Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues	11,410	10,841	33,686	32,104
Natural gas distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	2,708	3,208	9,544	10,821
Natural gas distribution | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	92,475	90,469	570,437	551,666
Natural gas distribution | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	1,167	1,779	(781)	2,786
Natural gas distribution | Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	44,902	43,825	316,521	305,399
Natural gas distribution | Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	29,148	28,174	192,191	185,885
Natural gas distribution | Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	4,307	4,421	18,495	17,457
Natural gas distribution | Other utility sales
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Pipeline and midstream
Disaggregation of Revenue [Line Items]
Revenues	32,533	29,071	69,827	61,965
Pipeline and midstream | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(3,831)	(3,187)	(35,298)	(31,485)
Pipeline and midstream | Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues	25,229	21,400	75,091	64,505
Pipeline and midstream | Natural gas gathering
Disaggregation of Revenue [Line Items]
Revenues	2,510	2,320	7,027	6,900
Pipeline and midstream | Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues	3,044	2,795	8,313	8,563
Pipeline and midstream | Other
Disaggregation of Revenue [Line Items]
Revenues	5,534	5,701	14,523	13,353
Pipeline and midstream | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	32,486	29,029	69,656	61,836
Pipeline and midstream | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	47	42	171	129
Construction materials and contracting
Disaggregation of Revenue [Line Items]
Revenues	869,376	743,763	1,692,287	1,466,435
Construction materials and contracting | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(124)	(165)	(388)	(501)
Construction materials and contracting | Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(231,078)	(204,040)	(412,144)	(363,877)
Construction materials and contracting | Contracting services
Disaggregation of Revenue [Line Items]
Revenues	461,716	409,006	841,881	730,628
Construction materials and contracting | Construction materials
Disaggregation of Revenue [Line Items]
Revenues	638,862	538,962	1,262,938	1,100,185
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	869,376	743,763	1,692,287	1,466,435
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	478,381	329,578	1,363,305	986,649
Construction services | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(1,226)	(782)	(2,076)	(1,332)
Construction services | Inside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	317,202	217,474	936,008	667,664
Construction services | Outside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	151,285	100,988	391,971	283,432
Construction services | Other
Disaggregation of Revenue [Line Items]
Revenues	45	15	70	32
Construction services | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	467,306	317,695	1,325,973	949,796
Construction services | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	11,075	11,883	37,332	36,853
Other
Disaggregation of Revenue [Line Items]
Revenues	22	47	65	193
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(2,862)	(3,037)	(13,566)	(8,343)
Other | Other
Disaggregation of Revenue [Line Items]
Revenues	2,884	3,084	13,631	8,536
Other | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	22	47	65	193
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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract assets	$ 163,437		$ 163,437		$ 104,239
Change in contract assets			59,198
Contract liabilities - current	(120,207)		(120,207)		(93,901)
Change in contract liabilities - current			(26,306)
Contract liabilities - noncurrent	(25)		(25)		(135)
Change in contract liabilities - noncurrent			110
Net contract assets	43,205		43,205		$ 10,203
Change in net contract assets			33,002
Amounts included in contract liability at the beginning of the period	7,500	$ 10,300	86,500	$ 79,200
Amounts from performance obligations satisfied in prior periods	$ 21,800	$ (8,700)	$ 40,300	$ (3,700)

Revenue from contracts with c_4

Revenue from contracts with customers Remaining performance obligations (Details 3) $ in Millions	Sep. 30, 2019USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 1,600
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	255
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	249.6
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 2,100

Business Combinations 2019 Busi

Business Combinations 2019 Business Combinations (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Business Combination, Consideration Transferred [Abstract]
Payments to Acquire Businesses, Gross	$ 54.5
Business Combination, Long-Term Debt Assumed	$ 1.2

2018 Business Combinations (Det

2018 Business Combinations (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 681,349	$ 640,203	$ 664,922	$ 631,791
Measurement Period Adjustments [Abstract]
Goodwill	(6,669)	$ 0	0
2018 Acquisitions [Member]
Business Acquisition [Line Items]
Receivables, net	18,984		18,984
Inventories	10,101		10,329
Prepayments and other current assets	501		515
Total current assets	29,586		29,828
Property, plant and equipment	138,435		131,766
Goodwill	26,462		33,131
Other Intangible assets, net	8,227		8,227
Other	927		927
Total deferred charges and other assets	35,616		42,285
Total assets acquired	203,637		203,879
Current liabilities	10,880		11,122
Asset retirement obligation	914		914
Deferred income taxes	5,565		5,565
Total deferred credits and other liabilities	6,479		6,479
Total liabilities assumed	17,359		17,601
Total consideration (fair value)	186,278		$ 186,278
Measurement Period Adjustments [Abstract]
Receivables, net	(228)
Inventories	(14)
Prepayments and other current assets	(242)
Property, plant and equipment	6,669
Goodwill	(6,669)
Total deferred charges and other assets	(6,669)
Total assets acquired	(242)
Current liabilities	(242)
Total liabilities assumed	$ (242)

Discontinued operations Noncont

Discontinued operations Noncontrolling interest (Details)	Jun. 27, 2016	Jun. 24, 2016
WBI Energy | Dakota Prairie Refining, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Previous percentage of ownership	50.00%	50.00%

Major classes of assets and lia

Major classes of assets and liabilities held for sale (Details 2) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Current assets:
Total current assets held for sale	$ 426	$ 430	$ 571
Noncurrent assets:
Total noncurrent assets held for sale	2,087	2,087	1,835
Current liabilities:
Total current liabilities held for sale	3,393	4,001	7,959
Discontinued operations, held-for-sale or disposed of by sale
Current assets:
Receivables, net	426	430	571
Income taxes receivable (a)	0	0	1,640
Total current assets held for sale	426	430	2,211
Noncurrent assets:
Deferred income taxes	1,926	1,926	1,711
Other	161	161	161
Total noncurrent assets held for sale	2,087	2,087	1,872
Total assets held for sale	2,513	2,517	4,083
Current liabilities:
Accounts payable	0	80	188
Taxes payable	1,300	1,451	7,463
Other accrued liabilities	2,093	2,470	1,948
Total current liabilities held for sale	3,393	4,001	9,599
Noncurrent liabilities:
Deferred income taxes (b)	0	0	37
Total noncurrent liabilities held for sale	0	0	37
Total liabilities held for sale	$ 3,393	$ 4,001	$ 9,636

Reconciliation of income and ex

Reconciliation of income and expenses (Details 3) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations	$ 1,509	$ (118)	$ 26	$ 85
Discontinued operations, held-for-sale or disposed of by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues	230	61	298	201
Operating expenses	(1,760)	216	264	825
Operating income (loss)	1,990	(155)	34	(624)
Other income	0	0	0	12
Interest expense	0	0	0	575
Income (loss) from discontinued operations before income taxes	1,990	(155)	34	(1,187)
Income taxes	481	(37)	8	(1,272)
Income (loss) from discontinued operations	$ 1,509	$ (118)	$ 26	$ 85

Lease costs (Details)

Lease costs (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)
Leases [Abstract]
Operating lease cost	$ 10,536	$ 32,444
Variable lease cost	381	1,180
Short-term lease cost	28,270	85,982
Total lease costs	$ 39,187	$ 119,606
Weighted average remaining lease term	2 years 11 months 23 days	2 years 11 months 23 days
Weighted average discount rate	4.63%	4.63%
Cash paid for amounts included in the measurement of lease liabilities		$ 32,261

Operating lease liabilities und

Operating lease liabilities undiscounted cash flows maturity schedule (Details 2) $ in Thousands	Sep. 30, 2019USD ($)
Leases [Abstract]
Remainder of 2019	$ 10,619
2020	32,605
2021	23,488
2022	15,838
2023	9,913
Thereafter	54,765
Total	147,228
Less discount	28,478
Total operating lease liabilities	$ 118,750

Leases Operating lease future m

Leases Operating lease future minimum lease payments (Details 3) $ in Thousands	Dec. 31, 2018USD ($)
Operating leases future minimum lease payments due [Abstract]
2019	$ 37,740
2020	26,255
2021	17,868
2022	11,647
2023	7,278
Thereafter	$ 49,098

Lessor accounting (Details 4)

Lessor accounting (Details 4) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)
Leases [Abstract]
Operating Lease, Lease Income	$ 11.2	$ 37.7
Lessor, Operating Lease, Payments to be Received, Next Twelve Months	$ 10	$ 10

Goodwill rollforward (Details)

Goodwill rollforward (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Goodwill [Roll Forward]
Balance at beginning of period	$ 664,922	$ 631,791	$ 631,791
Goodwill acquired during the year	23,096	8,412	33,131
Measurement period adjustments	(6,669)	0	0
Balance at end of period	681,349	640,203	664,922
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	209,421	176,290	176,290
Goodwill acquired during the year	14,473	8,412	33,131
Measurement period adjustments	(6,669)	0	0
Balance at end of period	217,225	184,702	209,421
Construction services
Goodwill [Roll Forward]
Balance at beginning of period	109,765	109,765	109,765
Goodwill acquired during the year	8,623	0	0
Measurement period adjustments	0	0	0
Balance at end of period	$ 118,388	$ 109,765	$ 109,765

Other intangible assets (Detail

Other intangible assets (Details 2) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 15,511,000	$ 4,318,000	$ 15,511,000	$ 4,318,000	$ 10,815,000
Amortization of intangible assets	500,000	300,000	1,600,000	900,000
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	18,011,000	15,920,000	18,011,000	15,920,000	22,720,000
Intangible assets, less accumulated amortization	5,823,000	13,342,000	5,823,000	13,342,000	13,535,000
Intangible assets, net (excluding goodwill)	12,188,000	2,578,000	12,188,000	2,578,000	9,185,000
Noncompete agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	3,419,000	2,606,000	3,419,000	2,606,000	2,605,000
Intangible assets, less accumulated amortization	1,868,000	1,911,000	1,868,000	1,911,000	1,956,000
Intangible assets, net (excluding goodwill)	1,551,000	695,000	1,551,000	695,000	649,000
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	7,488,000	6,458,000	7,488,000	6,458,000	6,458,000
Intangible assets, less accumulated amortization	5,716,000	5,413,000	5,716,000	5,413,000	5,477,000
Intangible assets, net (excluding goodwill)	$ 1,772,000	$ 1,045,000	1,772,000	$ 1,045,000	$ 981,000
Construction materials and contracting [Member] | Series of Individually Immaterial Business Acquisitions
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired			$ 6,300,000

Goodwill and other intangible_3

Goodwill and other intangible assets Future amortization expense (Details 3) $ in Thousands	Sep. 30, 2019USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2019	$ 931
2020	3,077
2021	2,042
2022	1,996
2023	1,957
Thereafter	$ 5,508

Regulatory assets and liabili_3

Regulatory assets and liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Regulatory Assets and Liabilities
Regulatory Assets	$ 431,591	$ 340,117
Regulatory Liabilities	490,317	521,432
Net Regulatory Position	(58,726)	(181,315)
Regulatory assets not earning a rate of return	278,200	313,500
Taxes recoverable from/refundable to customers
Regulatory Assets and Liabilities
Regulatory Liabilities	258,012	277,833
Plant removal
Regulatory Assets and Liabilities
Regulatory Liabilities	176,016	173,143
Natural gas costs refundable through rate adjustments
Regulatory Assets and Liabilities
Regulatory Liabilities	19,194	29,995
Pension and postretirement benefits
Regulatory Assets and Liabilities
Regulatory Liabilities	12,942	15,264
Other Regulatory Assets/Liabilities
Regulatory Assets and Liabilities
Regulatory Liabilities	$ 24,153	25,197
Pension and postretirement benefits
Regulatory Assets and Liabilities
Estimated Recovery Period	(e)
Regulatory Assets	$ 165,843	165,898
Natural gas costs recoverable through rate adjustments
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 3 years
Regulatory Assets	$ 93,001	42,652
Asset Retirement Obligation Costs
Regulatory Assets and Liabilities
Estimated Recovery Period	Over plant lives
Regulatory Assets	$ 64,771	60,097
Cost recovery mechanisms
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 4 years
Regulatory Assets	$ 20,912	17,948
Manufactured gas plant site remediation
Regulatory Assets and Liabilities
Estimated Recovery Period	-
Regulatory Assets	$ 15,739	17,068
Taxes recoverable from/refundable to customers
Regulatory Assets and Liabilities
Estimated Recovery Period	Over plant lives
Regulatory Assets	$ 11,600	11,946
Plant removal
Regulatory Assets and Liabilities
Estimated Recovery Period	-
Regulatory Assets	$ 26,152	0
Conservation programs
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 1 year
Regulatory Assets	$ 9,467	7,494
Long-term debt refinancing costs
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 19 years
Regulatory Assets	$ 4,439	4,898
Costs related to identifying generation development
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 8 years
Regulatory Assets	$ 2,166	2,508
Other Regulatory Assets/Liabilities
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 20 years
Regulatory Assets	$ 17,501	$ 9,608

Fair value measurements Insuran

Fair value measurements Insurance contracts (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Investments used to satisfy nonqualified benefit plans obligations	$ 84.2	$ 80.4	$ 84.2	$ 80.4	$ 73.8
Net unrealized gain (loss) on investments used to satisfy obligations under nonqualified benefit plans	$ 1.1	$ 2.1	$ 10.4	$ 3

Available-for-sale securities (

Available-for-sale securities (Details 2) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Available-for-sale securities [Abstract]
Cost	$ 10,835	$ 10,652	$ 10,729
Gross Unrealized Gains	86	21	3
Gross Unrealized Losses	17	162	251
Fair Value	10,904	10,511	10,481
Mortgage-backed securities
Available-for-sale securities [Abstract]
Cost	9,577	10,473	10,550
Gross Unrealized Gains	86	21	3
Gross Unrealized Losses	16	162	251
Fair Value	9,647	10,332	10,302
U.S. Treasury securities
Available-for-sale securities [Abstract]
Cost	1,258	179	179
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	1	0	0
Fair Value	$ 1,257	$ 179	$ 179

Fair value measurements (Detail

Fair value measurements (Details 3) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Concentration risks, percentage [Abstract]
Percentage in fixed-income and other investments	53.00%	53.00%	47.00%
Percentage investment in common stock of large-cap companies	21.00%	21.00%	24.00%
Percentage investment in common stock of mid-cap companies	11.00%	11.00%	13.00%
Percentage investment in common stock of small-cap companies	10.00%	10.00%	12.00%
Percentage investment in target date investments	3.00%	3.00%	3.00%
Percentage investment in cash and cash equivalents	2.00%	2.00%	1.00%
Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 102,598	$ 95,148	$ 100,787
Fair value, measurements, recurring | Money market funds
Fair value measurements [Line Items]
Assets, fair value disclosure	7,472	10,799	9,948
Fair value, measurements, recurring | Insurance contract
Fair value measurements [Line Items]
Assets, fair value disclosure	84,222	73,838	80,358
Fair value, measurements, recurring | Mortgage-backed securities
Fair value measurements [Line Items]
Assets, fair value disclosure	9,647	10,332	10,302
Fair value, measurements, recurring | U.S. Treasury securities
Fair value measurements [Line Items]
Assets, fair value disclosure	1,257	179	179
Fair value, measurements, recurring | Fair value, inputs, level 2
Fair value measurements [Line Items]
Assets, fair value disclosure	102,598	95,148	100,787
Fair value, measurements, recurring | Fair value, inputs, level 2 | Money market funds
Fair value measurements [Line Items]
Assets, fair value disclosure	7,472	10,799	9,948
Fair value, measurements, recurring | Fair value, inputs, level 2 | Insurance contract
Fair value measurements [Line Items]
Assets, fair value disclosure	84,222	73,838	80,358
Fair value, measurements, recurring | Fair value, inputs, level 2 | Mortgage-backed securities
Fair value measurements [Line Items]
Assets, fair value disclosure	9,647	10,332	10,302
Fair value, measurements, recurring | Fair value, inputs, level 2 | U.S. Treasury securities
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 1,257	$ 179	$ 179

Fair value measurements Fair va

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

Fair value measurements (Deta_2

Fair value measurements (Details 5) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Fair value, balance sheet grouping [Line Items]
Long-term debt	$ 2,246,756	$ 2,108,695
Carrying Amount
Fair value, balance sheet grouping [Line Items]
Long-term debt	2,246,756	2,108,695	$ 1,915,470
Fair Value
Fair value, balance sheet grouping [Line Items]
Long-term debt, fair value	$ 2,450,209	$ 2,183,819	$ 1,987,360

Short-term debt (Details)

Short-term debt (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Aug. 07, 2019	Apr. 12, 2019	Mar. 22, 2019	Dec. 31, 2018	Sep. 30, 2018
Short-term Debt [Line Items]
Short-term borrowings	$ 139,988				$ 0	$ 0
Cascade Natural Gas [Member] | Term Loan Agreements
Short-term Debt [Line Items]
Short-term borrowings				$ 40,000
Centennial Energy Holdings, Inc. [Member] | Term Loan Agreements
Short-term Debt [Line Items]
Short-term borrowings		$ 50,000	$ 50,000

Long-term debt Issued (Details

Long-term debt Issued (Details 2) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 13, 2019	Jun. 07, 2019	Apr. 04, 2019	Dec. 31, 2018	Apr. 25, 2017
Long-term debt issued [Line Items]
Long-term debt	$ 2,246,756				$ 2,108,695
Senior Notes
Long-term debt issued [Line Items]
Long-term debt	$ 1,655,000				1,381,000
Weighted Average Interest Rate	4.52%
Credit Agreements
Long-term debt issued [Line Items]
Long-term debt	$ 31,000				$ 110,100
Weighted Average Interest Rate	4.66%
Centennial Energy Holdings, Inc. [Member] | Senior Notes
Long-term debt issued [Line Items]
Long-term debt				$ 150,000
Weighted Average Interest Rate				4.60%
Cascade Natural Gas [Member] | Senior Notes
Long-term debt issued [Line Items]
Long-term debt		$ 75,000
Weighted Average Interest Rate		3.93%
Cascade Natural Gas [Member] | Credit Agreements
Long-term debt issued [Line Items]
Long-term debt			$ 100,000			$ 75,000
Intermountain Gas Company [Member] | Senior Notes
Long-term debt issued [Line Items]
Long-term debt		$ 50,000
Weighted Average Interest Rate		3.92%

Long-term debt outstanding (Det

Long-term debt outstanding (Details 3) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Long-term debt outstanding [Line Items]
Long-term debt	$ 2,246,756	$ 2,108,695
Long-term debt due within one year	65,810	251,854	$ 3,915
Long-term debt	$ 2,180,946	1,856,841	$ 1,911,555
Senior Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	4.52%
Long-term debt	$ 1,655,000	1,381,000
Commercial Paper
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	2.46%
Long-term debt	$ 281,800	338,100
Term Loan Agreements
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	2.75%
Long-term debt	$ 209,100	209,800
Credit Agreements
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	4.66%
Long-term debt	$ 31,000	110,100
Medium-term Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	6.68%
Long-term debt	$ 50,000	50,000
Other Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	5.01%
Long-term debt	$ 26,083	25,229
Long-term Debt
Long-term debt outstanding [Line Items]
Unamortized Debt Issuance Costs	6,074	5,207
Discount	$ 153	$ 327

Schedule of debt maturities (De

Schedule of debt maturities (Details 4) $ in Thousands	Sep. 30, 2019USD ($)
Long-term debt maturities [Line Items]
Remainder of 2019	$ 50,110
2020	15,902
2021	204,522
2022	147,402
2023	155,502
Thereafter	$ 1,679,545

Cash flow information (Details)

Cash flow information (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Interest, net	$ 64,596	$ 58,359
Income taxes paid, net	1,816	8,887
AFUDC borrowed	2,000	1,800
Right-of-use assets obtained in exchange for new operating lease liabilities	46,770
Property, plant and equipment additions in accounts payable	34,368	34,594	$ 42,355
Debt assumed in connection with a business combination	1,163
Issuance of common stock in connection with a business combination	0	17,993	$ 18,186
Continuing and discontinued operations
Income taxes paid, net	$ 2,000	$ 5,100

Business segment data (Details)

Business segment data (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 1,563,799			$ 1,280,787			$ 3,958,563	$ 3,321,678
Operating Income (Loss)	189,470			140,004			351,000	283,372
Income from continuing operations	136,128			107,369			240,362	193,405
Income (loss) from discontinued operations, net of tax	1,509			(118)			26	85
Net income	137,637	$ 61,825	$ 40,926	107,251	$ 43,802	$ 42,437	240,388	193,490
Electric
Segment Reporting Information [Line Items]
Revenues	89,845			86,080			263,423	251,984
Operating Income (Loss)	21,930			21,140			49,708	52,321
Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	93,642			92,248			569,656	554,452
Operating Income (Loss)	(15,565)			(11,665)			32,132	32,503
Pipeline and midstream
Segment Reporting Information [Line Items]
Revenues	32,533			29,071			69,827	61,965
Operating Income (Loss)	11,416			9,036			32,017	25,687
Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	869,376			743,763			1,692,287	1,466,435
Operating Income (Loss)	143,024			109,598			147,622	120,591
Construction services
Segment Reporting Information [Line Items]
Revenues	478,381			329,578			1,363,305	986,649
Operating Income (Loss)	29,950			11,863			89,381	51,853
Other
Segment Reporting Information [Line Items]
Revenues	22			47			65	193
Operating Income (Loss)	(1,285)			32			140	417
Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(8,043)			(7,171)			(51,328)	(41,661)
Intersegment eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	0			0			0	0
Intersegment eliminations | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	0			0			0	0
Intersegment eliminations | Pipeline and midstream
Segment Reporting Information [Line Items]
Revenues	(3,831)			(3,187)			(35,298)	(31,485)
Intersegment eliminations | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	(124)			(165)			(388)	(501)
Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	(1,226)			(782)			(2,076)	(1,332)
Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	(2,862)			(3,037)			(13,566)	(8,343)
Total intersegment operating revenues
Segment Reporting Information [Line Items]
Revenues	0			0			0	0
Regulated operation
Segment Reporting Information [Line Items]
Revenues	209,444			200,617			885,309	851,761
Income from continuing operations	7,599			13,506			74,206	72,193
Regulated operation | Electric
Segment Reporting Information [Line Items]
Revenues	89,845			86,080			263,423	251,984
Income from continuing operations	16,291			15,284			39,267	37,500
Regulated operation | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	93,642			92,248			569,656	554,452
Income from continuing operations	(15,625)			(11,887)			14,623	13,884
Regulated operation | Pipeline and midstream
Segment Reporting Information [Line Items]
Revenues	25,957			22,289			52,230	45,325
Income from continuing operations	6,933			10,109			20,316	20,809
Regulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	3,750			3,070			35,098	31,252
Regulated operation | Intersegment eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	0			0			0	0
Regulated operation | Intersegment eliminations | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	0			0			0	0
Regulated operation | Intersegment eliminations | Pipeline and midstream
Segment Reporting Information [Line Items]
Revenues	3,750			3,070			35,098	31,252
Nonregulated operation
Segment Reporting Information [Line Items]
Revenues	1,354,355			1,080,170			3,073,254	2,469,917
Income from continuing operations	128,529			93,863			166,156	121,212
Nonregulated operation | Pipeline and midstream
Segment Reporting Information [Line Items]
Revenues	6,576			6,782			17,597	16,640
Income from continuing operations	801			848			1,380	1,136
Nonregulated operation | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	869,376			743,763			1,692,287	1,466,435
Income from continuing operations	102,611			78,876			97,328	79,691
Nonregulated operation | Construction services
Segment Reporting Information [Line Items]
Revenues	478,381			329,578			1,363,305	986,649
Income from continuing operations	21,113			9,278			63,982	38,457
Nonregulated operation | Other
Segment Reporting Information [Line Items]
Revenues	22			47			65	193
Income from continuing operations	4,004			4,861			3,466	1,928
Nonregulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	4,293			4,101			16,230	10,409
Nonregulated operation | Intersegment eliminations | Pipeline and midstream
Segment Reporting Information [Line Items]
Revenues	81			117			200	233
Nonregulated operation | Intersegment eliminations | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	124			165			388	501
Nonregulated operation | Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	1,226			782			2,076	1,332
Nonregulated operation | Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	$ 2,862			$ 3,037			$ 13,566	$ 8,343

Employee benefit plans (Details

Employee benefit plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Qualified plan | Underfunded plan | Pension benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	3,806	3,648	11,419	10,943
Expected return on assets	(4,559)	(5,188)	(13,677)	(15,565)
Amortization of prior service credit	0	0	0	0
Amortization of net actuarial loss	1,387	1,751	4,160	5,254
Net periodic benefit cost (credit), including amount capitalized	634	211	1,902	632
Less amount capitalized	0	0	0	0
Net periodic benefit cost (credit)	634	211	1,902	632
Qualified plan | Overfunded Plan [Member] | Other postretirement benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	286	374	857	1,121
Interest cost	746	725	2,239	2,175
Expected return on assets	(1,201)	(1,217)	(3,603)	(3,650)
Amortization of prior service credit	(289)	(349)	(866)	(1,046)
Amortization of net actuarial loss	27	160	82	480
Net periodic benefit cost (credit), including amount capitalized	(431)	(307)	(1,291)	(920)
Less amount capitalized	26	46	84	128
Net periodic benefit cost (credit)	(457)	(353)	(1,375)	(1,048)
Nonqualified plan | Unfunded plan | Supplemental employee retirement plans
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Net periodic benefit cost (credit)	$ 1,100	$ 1,100	$ 3,300	$ 3,300

MNPUC (Details)

MNPUC (Details) - MNPUC [Member] - Gas Distribution [Member] - Great Plains Natural Gas Co. [Member] - USD ($)	Sep. 27, 2019	May 01, 2019	Sep. 16, 2019
Pending Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 2,900,000
Public Utilities, Requested Rate Increase (Decrease), Percentage	12.00%
Public Utilities, Interim Rate Increase (Decrease), Amount	$ 2,600,000
Public Utilities, Interim Rate Increase (Decrease), Percentage	11.00%
Tax Cuts and Jobs Act [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ (400,000)
Approved Customer Refunds			$ (600,000)

MTPSC (Details 2)

MTPSC (Details 2) - MTPSC - Electricity [Member] - Montana-Dakota Utilities Co. [Member] - USD ($)	Sep. 01, 2020	Sep. 01, 2019
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 9,000,000
Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 300,000

NDPSC (Details 3)

NDPSC (Details 3) $ in Millions	Oct. 28, 2019USD ($)
NDPSC | Electricity [Member] | Montana-Dakota Utilities Co. [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 1.5

OPUC (Details 4)

OPUC (Details 4) $ in Millions	12 Months Ended
	Oct. 31, 2020USD ($)
OPUC | Gas Distribution [Member] | Cascade Natural Gas [Member] | Tax Cuts and Jobs Act [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Approved Customer Refunds	$ (1.4)

WUTC (Details 5)

WUTC (Details 5) - WUTC - Cascade Natural Gas [Member] - USD ($)	Nov. 01, 2019	Sep. 20, 2019	May 31, 2019	Mar. 29, 2019
Gas Distribution [Member] | Pending Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 12,700,000
Public Utilities, Requested Rate Increase (Decrease), Percentage				5.50%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount		$ 6,500,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage		2.80%
Pipeline Cost Recovery Mechanism [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 1,600,000
Public Utilities, Requested Rate Increase (Decrease), Percentage			0.70%
Pipeline Cost Recovery Mechanism [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 440,000
Public Utilities, Approved Rate Increase (Decrease), Percentage	0.20%
Purchased Gas Adjustment [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 12,800,000
Public Utilities, Approved Rate Increase (Decrease), Percentage	5.70%
Purchased Gas Costs Recovery Period	3 years

WYPSC (Details 6)

WYPSC (Details 6) - WYPSC - Montana-Dakota Utilities Co. [Member] - USD ($)	Nov. 01, 2019	Jul. 25, 2019	May 23, 2019	May 01, 2019
Electricity [Member] | Tax Cuts and Jobs Act [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount				$ (1,100,000)
Public Utilities, Approved Rate Increase (Decrease), Percentage				(4.20%)
Approved Customer Refunds		$ (1,600,000)
Gas Distribution [Member] | Pending Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 1,100,000
Public Utilities, Requested Rate Increase (Decrease), Percentage			7.00%
Gas Distribution [Member] | Tax Cuts and Jobs Act [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Approved Customer Refunds	$ (200,000)

FERC (Details 7)

FERC (Details 7) - USD ($) $ in Millions	Jan. 01, 2020	May 01, 2019
FERC [Member] | Gas Distribution [Member] | WBI Energy Transmission, Inc. [Member] | Tax Cuts and Jobs Act [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 4.5
MISO [Member] | Electricity [Member] | Montana-Dakota Utilities Co. [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Transmission Formula Revenue Requirement	$ 13.4

Litigation (Details)

Litigation (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Loss Contingencies [Line Items]
Potential liabilities related to litigation and environmental matters	$ 30.6	$ 30.4	$ 30.4

Environmental matters (Details

Environmental matters (Details 2) - USD ($)	9 Months Ended
	Sep. 30, 2019	Jan. 06, 2017
Portland Harbor Site
Site Contingency [Line Items]
Environmental matters investigative costs	$ 100,000,000
Environmental matters, estimated costs		$ 1,000,000,000
Missoula, MT manufactured gas plant site
Site Contingency [Line Items]
Total estimated costs for site remediation	560,000
Environmental matters accrual for site remediation	375,000
Bremerton, WA manufactured gas plant site
Site Contingency [Line Items]
Environmental matters accrual for site remediation	6,400,000
Total estimated costs for site remedial investigation and feasibility study	7,600,000
Incurred costs for site remedial investigation and feasibility study	3,800,000
Environmental matters accrual of investigative costs	3,800,000
Bellingham, WA manufactured gas plant site
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, preferred alternative estimate	9,300,000
Minimum | Bremerton, WA manufactured gas plant site
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	340,000
Minimum | Bellingham, WA manufactured gas plant site
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	8,000,000
Maximum | Bremerton, WA manufactured gas plant site
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	6,400,000
Maximum | Bellingham, WA manufactured gas plant site
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	$ 20,400,000

Guarantees (Details 3)

Guarantees (Details 3)	Sep. 30, 2019USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 206,500,000
Fixed maximum amounts guaranteed by year 2019	2,000,000
Fixed maximum amounts guaranteed by year 2020	192,200,000
Fixed maximum amounts guaranteed by year 2021	700,000
Fixed maximum amounts guaranteed by year 2022	500,000
Fixed maximum amounts guaranteed by year 2023	500,000
Fixed maximum amounts guaranteed, thereafter	1,600,000
No scheduled maturity date	9,000,000
Amount outstanding under guarantees that is reflected on balance sheet	0
Letters of credit	30,000,000
Letters of credit set to expire - 2019	24,400,000
Letters of credit set to expire - 2020	5,600,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	$ 930,100,000

Variable interest entities (Det

Variable interest entities (Details 4) $ in Millions	Sep. 30, 2019USD ($)
Fuel contract
Variable Interest Entities [Line Items]
Variable interest entity, reporting entity involvement, maximum loss exposure, amount	$ 36.6