MDU Resources (MDU) 10-Q 2 Aug 19 2019 Q2 Quarterly report Financial data

Cover page

Cover page - shares	6 Months Ended
	Jun. 30, 2019	Jul. 26, 2019
Entity Information [Line Items]
Document type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 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		199,058,947
Entity Central Index Key	0000067716
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Amendment Flag	false

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating revenues:
Operating revenues:	$ 1,303,573	$ 1,064,597	$ 2,394,764	$ 2,040,890
Operating expenses:
Operation and maintenance:	1,021,031	822,084	1,723,945	1,422,940
Purchased natural gas sold	54,866	56,228	238,695	238,196
Depreciation, depletion and amortization	63,019	53,553	122,916	106,282
Taxes, other than income	47,953	40,757	101,982	89,610
Electric fuel and purchased power	19,393	17,983	45,696	40,494
Total operating expenses	1,206,262	990,605	2,233,234	1,897,522
Operating income	97,311	73,992	161,530	143,368
Other income	1,615	1,599	9,208	2,181
Interest expense	25,429	20,800	48,836	41,246
Income before income taxes	73,497	54,791	121,902	104,303
Income taxes	10,352	10,716	17,668	18,267
Income from continuing operations	63,145	44,075	104,234	86,036
Income (loss) from discontinued operations, net of tax (Note 10)	(1,320)	(273)	(1,483)	203
Net income	$ 61,825	$ 43,802	$ 102,751	$ 86,239
Earnings per share - basic:
Income from continuing operations	$ 0.32	$ 0.22	$ 0.53	$ 0.44
Discontinued operations, net of tax	(0.01)	0	(0.01)	0
Earnings per share - basic	0.31	0.22	0.52	0.44
Earnings per share - diluted:
Income from continuing operations	0.32	0.22	0.53	0.44
Discontinued operations, net of tax	(0.01)	0	(0.01)	0
Earnings per share - diluted	$ 0.31	$ 0.22	$ 0.52	$ 0.44
Weighted average common shares outstanding - basic	198,270	195,524	197,341	195,415
Weighted average common shares outstanding - diluted	198,287	196,169	197,356	196,077
Regulated operation
Operating revenues:
Operating revenues:	$ 236,247	$ 226,684	$ 675,864	$ 651,143
Operating expenses:
Operation and maintenance:	88,415	83,928	176,186	170,042
Income from continuing operations	7,597	7,521	66,606	58,686
Nonregulated operation
Operating revenues:
Operating revenues:	1,067,326	837,913	1,718,900	1,389,747
Operating expenses:
Operation and maintenance:	932,616	738,156	1,547,759	1,252,898
Income from continuing operations	$ 55,548	$ 36,554	$ 37,628	$ 27,350

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net income	$ 61,825	$ 43,802	$ 102,751	$ 86,239
Other comprehensive income:
Reclassification adjustment for loss on derivative instruments included in net income, net of tax of $36 and $53 for the three months ended and $(213) and $109 for the six months ended in 2019 and 2018, respectively	111	95	508	187
Postretirement liability adjustment:
Amortization of postretirement liability losses included in net periodic benefit cost, net of tax of $89 and $145 for the three months ended and $189 and $300 for the six months ended in 2019 and 2018, respectively	276	449	586	867
Foreign currency translation adjustment:
Foreign currency translation adjustment recognized during the period, net of tax of $0 and $(13) for the three months ended and $0 and $(14) for the six months ended in 2019 and 2018, respectively	0	(59)	0	(61)
Reclassification adjustment for foreign currency translation adjustment included in net income, net of tax of $0 and $75 for the three months ended and $0 and $75 for the six months ended in 2019 and 2018, respectively	0	249	0	249
Foreign currency translation adjustment	0	190	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 $21 and $(12) for the three months ended and $31 and $(39) for the six months ended in 2019 and 2018, respectively	79	(43)	118	(148)
Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax of $3 and $10 for the three months ended and $10 and $17 for the six months ended in 2019 and 2018, respectively	12	34	40	64
Net unrealized gain (loss) on available-for-sale investments	91	(9)	158	(84)
Other comprehensive income	478	725	1,252	1,158
Comprehensive income attributable to common stockholders	$ 62,303	$ 44,527	$ 104,003	$ 87,397

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income - Parenthetical - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification adjustment for loss on derivative instruments included in net income, tax	$ 36	$ 53	$ (213)	$ 109
Amortization of postretirement liability losses included in net periodic benefit cost, tax	89	145	189	300
Foreign currency translation adjustments recognized during the period, tax	0	(13)	0	(14)
Reclassification of foreign currency translation adjustment	0	75	0	75
Net unrealized gain (loss) on available-for-sale investments arising during the period, tax	21	(12)	31	(39)
Reclassification adjustment for loss on available-for-sale investments included in net income, tax	$ 3	$ 10	$ 10	$ 17

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Current assets:
Cash and cash equivalents	$ 71,966	$ 53,948	$ 41,659
Receivables, net	890,579	722,945	743,687
Inventories	325,944	287,309	278,239
Prepayments and other current assets	155,893	119,500	52,035
Current assets held for sale	428	430	572
Total current assets	1,444,810	1,184,132	1,116,192
Investments	145,746	138,620	140,053
Property, plant and equipment	7,625,654	7,397,321	6,975,919
Less accumulated depreciation, depletion and amortization	2,903,274	2,818,644	2,758,163
Net property, plant and equipment	4,722,380	4,578,677	4,217,756
Deferred charges and other assets:
Goodwill	679,395	664,922	642,374
Other intangible assets, net	11,323	10,815	4,190
Operating lease right-of-use assets (Note 11)	118,795	0	0
Other	466,957	408,857	409,407
Noncurrent assets held for sale	2,087	2,087	3,998
Total deferred charges and other assets	1,278,557	1,086,681	1,059,969
Total assets	7,591,493	6,988,110	6,533,970
Current liabilities:
Short-term borrowings	89,983	0	0
Long-term debt due within one year	51,822	251,854	109,199
Accounts payable	356,059	358,505	330,926
Taxes payable	46,731	41,929	47,803
Dividends payable	40,225	39,695	38,714
Accrued compensation	71,508	69,007	53,933
Current operating lease liabilities (Note 11)	31,615	0	0
Other accrued liabilities	218,442	221,059	208,696
Current liabilities held for sale	6,217	4,001	11,713
Total current liabilities	912,602	986,050	800,984
Long-term debt	2,327,984	1,856,841	1,743,711
Deferred credits and other liabilities:
Deferred income taxes	457,588	430,085	362,896
Noncurrent operating lease liabilities (Note 11)	87,172	0	0
Other	1,145,846	1,148,359	1,175,301
Total deferred credits and other liabilities	1,690,606	1,578,444	1,538,197
Commitments and contingencies
Stockholders' equity:
Authorized - 500,000,000 shares, $1.00 par value Shares issued - 199,539,110 at June 30, 2019, 196,557,245 at June 30, 2018 and 196,564,907 at December 31, 2018	199,539	196,565	196,557
Other paid-in capital	1,315,511	1,248,576	1,245,858
Retained earnings	1,185,967	1,163,602	1,056,424
Accumulated other comprehensive loss	(37,090)	(38,342)	(44,135)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)	(3,626)
Total stockholders' equity	2,660,301	2,566,775	2,451,078
Total liabilities and stockholders' equity	$ 7,591,493	$ 6,988,110	$ 6,533,970

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Stockholders' equity:
Common stock, shares issued	199,539,110	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	86,239
Other comprehensive income	1,158
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	$ (2,330)
Balance (in shares) at Jun. 30, 2018	196,557,245	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)
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	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)
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	102,751
Other comprehensive income	1,252
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	$ (3,015)
Balance (in shares) at Jun. 30, 2019	199,539,110	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)
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	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)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Net income	$ 102,751	$ 86,239
Operating activities:
Income (loss) from discontinued operations, net of tax	(1,483)	203
Income from continuing operations	104,234	86,036
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation, depletion and amortization	122,916	106,282
Deferred income taxes	22,753	4,186
Changes in current assets and liabilities, net of acquisitions:
Receivables	(171,304)	(13,853)
Inventories	(36,302)	(47,396)
Other current assets	(32,088)	29,072
Accounts payable	1,398	15,748
Other current liabilities	15,585	7,849
Other noncurrent changes	(50,822)	(11,566)
Net cash provided by (used in) continuing operations	(23,630)	176,358
Net cash provided by discontinued operations	735	224
Net cash provided by (used in) operating activities	(22,895)	176,582
Investing activities:
Capital expenditures	(281,674)	(210,612)
Acquisitions, net of cash acquired	(30,868)	(20,009)
Net proceeds from sale or disposition of property and other	8,197	9,286
Investments	(713)	(916)
Net cash used in investing activities	(305,058)	(222,251)
Financing activities:
Issuance of short-term borrowings	119,977	0
Repayment of short-term borrowings	(30,000)	0
Issuance of long-term debt	368,975	240,746
Repayment of long-term debt	(99,961)	(103,521)
Proceeds from issuance of common stock	69,565	0
Dividends paid	(79,570)	(77,145)
Repurchase of common stock	0	(5,020)
Tax withholding on stock-based compensation	(3,015)	(2,330)
Net cash provided by financing activities	345,971	52,730
Effect of Exchange Rate on Cash and Cash Equivalents	0	(1)
Increase in cash and cash equivalents	18,018	7,060
Cash and cash equivalents -- beginning of year	53,948	34,599
Cash and cash equivalents -- end of period	$ 71,966	$ 41,659

Basis of presentation

Basis of presentation	6 Months Ended
	Jun. 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 June 30, 2019 , up to the date of issuance of these consolidated interim financial statements.

Seasonality of operations

Seasonality of operations	6 Months Ended
	Jun. 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	6 Months Ended
	Jun. 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 $47.2 million , $36.6 million and $30.0 million at June 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 June 30, 2019 and 2018 , and December 31, 2018 , was $8.2 million , $7.8 million and $8.9 million , respectively.

Inventories and natural gas in

Inventories and natural gas in storage	6 Months Ended
	Jun. 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: June 30, 2019 June 30, 2018 December 31, 2018 (In thousands) Aggregates held for resale $ 147,030 $ 131,784 $ 139,681 Asphalt oil 80,418 64,560 54,741 Materials and supplies 28,746 24,688 23,611 Merchandise for resale 27,167 17,502 22,552 Natural gas in storage (current) 15,841 13,774 22,117 Other 26,742 25,931 24,607 Total $ 325,944 $ 278,239 $ 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 June 30, 2019 and 2018 , and December 31, 2018 , respectively.

Earnings per common share

Earnings per common share	6 Months Ended
	Jun. 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 Six Months Ended June 30, June 30, 2019 2018 2019 2018 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 198,270 195,524 197,341 195,415 Effect of dilutive performance share awards and restricted stock units 17 645 15 662 Weighted average common shares outstanding - diluted 198,287 196,169 197,356 196,077 Shares excluded from the calculation of diluted earnings per share — — 93 — Dividends declared per common share $ .2025 $ .1975 $ .4050 $ .3950

New accounting standards

New accounting standards	6 Months Ended
	Jun. 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, and 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 does not expect the guidance to have a material impact on its results of operations, financial position, cash flows and 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 is evaluating the guidance and does not expect it to have a material impact on its results of operations, financial position, cash flows and disclosures. 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)	6 Months Ended
	Jun. 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: Six Months Ended June 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 ) Six Months Ended June 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 ) The following amounts were reclassified out of accumulated other comprehensive loss into net income. The amounts presented in parenthesis indicate a decrease to net income on the Consolidated Statements of Income. The reclassifications were as follows: Three Months Ended Six Months Ended Location on Consolidated Statements of Income June 30, June 30, 2019 2018 2019 2018 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ (147 ) $ (148 ) $ (295 ) $ (296 ) Interest expense 36 53 (213 ) 109 Income taxes (111 ) (95 ) (508 ) (187 ) Amortization of postretirement liability losses included in net periodic benefit cost (credit) (365 ) (594 ) (775 ) (1,167 ) Other income 89 145 189 300 Income taxes (276 ) (449 ) (586 ) (867 ) Reclassification adjustment for loss on foreign currency translation adjustment included in net income — (324 ) — (324 ) Other income — 75 — 75 Income taxes — (249 ) — (249 ) Reclassification adjustment on available-for-sale investments included in net income (15 ) (44 ) (50 ) (81 ) Other income 3 10 10 17 Income taxes (12 ) (34 ) (40 ) (64 ) Total reclassifications $ (399 ) $ (827 ) $ (1,134 ) $ (1,367 )

Revenue from contracts with cus

Revenue from contracts with customers	6 Months Ended
	Jun. 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 one year 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 June 30, 2019 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 26,437 $ 71,010 $ — $ — $ — $ — $ 97,447 Commercial utility sales 33,231 41,250 — — — — 74,481 Industrial utility sales 9,344 5,577 — — — — 14,921 Other utility sales 1,879 — — — — — 1,879 Natural gas transportation — 10,706 24,804 — — — 35,510 Natural gas gathering — — 2,396 — — — 2,396 Natural gas storage — — 2,623 — — — 2,623 Contracting services — — — 297,124 — — 297,124 Construction materials — — — 444,768 — — 444,768 Intrasegment eliminations* — — — (145,925 ) — — (145,925 ) Inside specialty contracting — — — — 319,276 — 319,276 Outside specialty contracting — — — — 133,288 — 133,288 Other 8,417 2,923 6,293 — 9 2,903 20,545 Intersegment eliminations — — (7,513 ) (168 ) (721 ) (2,879 ) (11,281 ) Revenues from contracts with customers 79,308 131,466 28,603 595,799 451,852 24 1,287,052 Revenues out of scope 1,703 2,401 77 — 12,340 — 16,521 Total external operating revenues $ 81,011 $ 133,867 $ 28,680 $ 595,799 $ 464,192 $ 24 $ 1,303,573 * 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 June 30, 2018 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 26,752 $ 68,688 $ — $ — $ — $ — $ 95,440 Commercial utility sales 32,676 40,820 — — — — 73,496 Industrial utility sales 8,226 5,227 — — — — 13,453 Other utility sales 1,874 — — — — — 1,874 Natural gas transportation — 10,084 21,287 — — — 31,371 Natural gas gathering — — 2,310 — — — 2,310 Natural gas storage — — 2,634 — — — 2,634 Contracting services — — — 247,558 — — 247,558 Construction materials — — — 387,632 — — 387,632 Intrasegment eliminations* — — — (125,567 ) — — (125,567 ) Inside specialty contracting — — — — 216,371 — 216,371 Outside specialty contracting — — — — 95,261 — 95,261 Other 8,425 3,614 4,326 — 103 2,757 19,225 Intersegment eliminations — — (6,539 ) (235 ) (540 ) (2,667 ) (9,981 ) Revenues from contracts with customers 77,953 128,433 24,018 509,388 311,195 90 1,051,077 Revenues out of scope 546 1,107 42 — 11,825 — 13,520 Total external operating revenues $ 78,499 $ 129,540 $ 24,060 $ 509,388 $ 323,020 $ 90 $ 1,064,597 * 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. Six Months Ended June 30, 2019 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 62,993 $ 271,619 $ — $ — $ — $ — $ 334,612 Commercial utility sales 68,902 163,043 — — — — 231,945 Industrial utility sales 18,228 14,188 — — — — 32,416 Other utility sales 3,678 — — — — — 3,678 Natural gas transportation — 22,276 49,862 — — — 72,138 Natural gas gathering — — 4,517 — — — 4,517 Natural gas storage — — 5,269 — — — 5,269 Contracting services — — — 380,164 — — 380,164 Construction materials — — — 624,077 — — 624,077 Intrasegment eliminations* — — — (181,066 ) — — (181,066 ) Inside specialty contracting — — — — 618,805 — 618,805 Outside specialty contracting — — — — 240,686 — 240,686 Other 17,538 6,836 8,989 — 26 10,747 44,136 Intersegment eliminations — — (31,468 ) (264 ) (849 ) (10,704 ) (43,285 ) Revenues from contracts with customers 171,339 477,962 37,169 822,911 858,668 43 2,368,092 Revenues out of scope 2,239 (1,948 ) 124 — 26,257 — 26,672 Total external operating revenues $ 173,578 $ 476,014 $ 37,293 $ 822,911 $ 884,925 $ 43 $ 2,394,764 * 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. Six Months Ended June 30, 2018 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 61,935 $ 261,574 $ — $ — $ — $ — $ 323,509 Commercial utility sales 67,377 157,711 — — — — 225,088 Industrial utility sales 16,996 13,036 — — — — 30,032 Other utility sales 3,710 — — — — — 3,710 Natural gas transportation — 21,263 43,105 — — — 64,368 Natural gas gathering — — 4,580 — — — 4,580 Natural gas storage — — 5,768 — — — 5,768 Contracting services — — — 321,622 — — 321,622 Construction materials — — — 561,223 — — 561,223 Intrasegment eliminations* — — — (159,837 ) — — (159,837 ) Inside specialty contracting — — — — 450,192 — 450,192 Outside specialty contracting — — — — 182,442 — 182,442 Other 16,678 7,613 7,652 — 17 5,452 37,412 Intersegment eliminations — — (28,298 ) (336 ) (550 ) (5,306 ) (34,490 ) Revenues from contracts with customers 166,696 461,197 32,807 722,672 632,101 146 2,015,619 Revenues out of scope (792 ) 1,007 86 — 24,970 — 25,271 Total external operating revenues $ 165,904 $ 462,204 $ 32,893 $ 722,672 $ 657,071 $ 146 $ 2,040,890 * 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: June 30, 2019 December 31, 2018 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 153,641 $ 104,239 $ 49,402 Receivables, net Contract liabilities - current (90,031 ) (93,901 ) 3,870 Accounts payable Contract liabilities - noncurrent (25 ) (135 ) 110 Deferred credits and other liabilities - other Net contract assets $ 63,585 $ 10,203 $ 53,382 The Company recognized $22.6 million and $79.0 million in revenue for the three and six months ended June 30, 2019 , respectively, which was previously included in contract liabilities at December 31, 2018 . The Company recognized $16.9 million and $68.9 million in revenue for the three and six months ended June 30, 2018 , respectively, which was previously included in contract liabilities at December 31, 2017 . The Company recognized a net increase in revenues of $20.6 million and $32.5 million for the three and six months ended June 30, 2019 , respectively, from performance obligations satisfied in prior periods. The Company recognized a net increase in revenues of $2.6 million and $5.3 million for the three and six months ended June 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 June 30, 2019 , the Company's remaining performance obligations were $2.3 billion . The Company expects to recognize the following revenue amounts in future periods related to these remaining performance obligations: $1.8 billion within the next 12 months; $269.4 million within the next 13 to 24 months; and $248.6 million thereafter.

Business Combinations

Business Combinations	6 Months Ended
	Jun. 30, 2019
Business Acquisition [Line Items]
Business Combinations	Business combinations In March 2019, the Company acquired Viesko Redi-Mix, Inc., a provider of ready-mixed concrete in Oregon. The gross aggregate consideration for this acquisition was $32.1 million , subject to certain adjustments, which includes $1.2 million of debt assumed. The acquisition is 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 all business combinations that occurred during 2018 have been settled and the purchase price allocations are considered final; except for Sweetman Construction Company, which was acquired in October 2018. No material adjustments were made to the provisional accounting for the business combinations. 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 construction materials and contracting segment and 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. However, any subsequent measurement period adjustments are not expected to have a material impact on the Company's results of operations.

Discontinued operations

Discontinued operations	6 Months Ended
	Jun. 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. In connection with the sale of Dakota Prairie Refining, Centennial guaranteed certain debt obligations of Dakota Prairie Refining and Tesoro agreed to indemnify Centennial for any losses and litigation expenses arising from the guarantee. On October 17, 2018, Centennial was released of any further liabilities or obligations under this guarantee. 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: June 30, 2019 June 30, 2018 December 31, 2018 (In thousands) Assets Current assets: Receivables, net $ 428 $ 572 $ 430 Income taxes receivable (a) — 1,689 — Total current assets held for sale 428 2,261 430 Noncurrent assets: Net property, plant and equipment — 1,236 — Deferred income taxes 1,926 2,637 1,926 Other 161 162 161 Total noncurrent assets held for sale 2,087 4,035 2,087 Total assets held for sale $ 2,515 $ 6,296 $ 2,517 Liabilities Current liabilities: Accounts payable $ 82 $ — $ 80 Taxes payable 3,114 10,656 1,451 Other accrued liabilities 3,021 2,746 2,470 Total current liabilities held for sale 6,217 13,402 4,001 Noncurrent liabilities: Deferred income taxes (b) — 37 — Total noncurrent liabilities held for sale — 37 — Total liabilities held for sale $ 6,217 $ 13,439 $ 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 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 Six Months Ended June 30, June 30, 2019 2018 2019 2018 (In thousands) Operating revenues $ 37 $ 75 $ 67 $ 140 Operating expenses 1,778 435 2,023 609 Operating loss (1,741 ) (360 ) (1,956 ) (469 ) Other income — — — 12 Interest expense — — — 575 Loss from discontinued operations before income taxes (1,741 ) (360 ) (1,956 ) (1,032 ) Income taxes (421 ) (87 ) (473 ) (1,235 ) Income (loss) from discontinued operations $ (1,320 ) $ (273 ) $ (1,483 ) $ 203

Leases

Leases	6 Months Ended
	Jun. 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 Six Months Ended June 30, June 30, 2019 2019 (In thousands) Lease costs: Operating lease cost $ 10,387 $ 21,908 Variable lease cost 400 799 Short-term lease cost 40,474 57,712 Total lease costs $ 51,261 $ 80,419 June 30, 2019 (Dollars in thousands) Weighted average remaining lease term 3.02 years Weighted average discount rate 4.46 % Cash paid for amounts included in the measurement of lease liabilities $ 21,798 The reconciliation of the future undiscounted cash flows to the operating lease liabilities presented on the Company's Consolidated Balance Sheet is as follows: June 30, 2019 (In thousands) Remainder of 2019 $ 19,276 2020 30,065 2021 22,850 2022 14,816 2023 8,941 Thereafter 51,335 Total 147,283 Less discount 28,496 Total operating lease liabilities $ 118,787 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 $12.5 million and $26.5 million for the three and six months ended June 30, 2019 , respectively. The majority of the Company's operating leases are short-term leases of less than 12 months. At June 30, 2019 , the Company had $10.6 million of lease receivables with a majority due within 12 months.

Goodwill and other intangible a

Goodwill and other intangible assets	6 Months Ended
	Jun. 30, 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: Six Months Ended June 30, 2019 Balance at January 1, 2019 Goodwill Acquired the Year Balance at June 30, 2019 (In thousands) Natural gas distribution $ 345,736 $ — $ 345,736 Construction materials and contracting 209,421 14,473 223,894 Construction services 109,765 — 109,765 Total $ 664,922 $ 14,473 $ 679,395 Six Months Ended June 30, 2018 Balance at January 1, 2018 Goodwill Acquired the Year Balance at June 30, 2018 (In thousands) Natural gas distribution $ 345,736 $ — $ 345,736 Construction materials and contracting 176,290 10,583 186,873 Construction services 109,765 — 109,765 Total $ 631,791 $ 10,583 $ 642,374 Year Ended December 31, 2018 Balance at January 1, 2018 Goodwill Acquired the Year 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 one and four business combinations, respectively, and the results of the acquired businesses have been included in the Company's construction materials and contracting segment. These business combinations increased the construction materials and contracting segment's goodwill balance at June 30, 2019 and 2018, and December 31, 2018, as noted in the previous tables. As a result of the business combinations, other intangible assets increased $1.6 million at June 30, 2019, compared to December 31, 2018. For more information related to business combinations, see Note 9 . Other amortizable intangible assets were as follows: June 30, 2019 June 30, 2018 December 31, 2018 (In thousands) Customer relationships $ 14,601 $ 15,587 $ 22,720 Less accumulated amortization 5,629 13,191 13,535 8,972 2,396 9,185 Noncompete agreements 3,179 2,546 2,605 Less accumulated amortization 1,798 1,877 1,956 1,381 669 649 Other 6,578 6,458 6,458 Less accumulated amortization 5,608 5,333 5,477 970 1,125 981 Total $ 11,323 $ 4,190 $ 10,815 Amortization expense for amortizable intangible assets for the three and six months ended June 30, 2019 , was $500,000 and $1.1 million , respectively. Amortization expense for amortizable intangible assets for the three and six months ended June 30, 2018 , was $300,000 and $700,000 , respectively. Estimated amortization expense for identifiable intangible assets as of June 30, 2019 , was: Remainder of 2019 2020 2021 2022 2023 Thereafter (In thousands) Amortization expense $ 938 $ 1,644 $ 1,254 $ 1,231 $ 1,249 $ 5,007

Regulatory assets and liabiliti

Regulatory assets and liabilities	6 Months Ended
	Jun. 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 * June 30, 2019 December 31, 2018 (In thousands) Regulatory assets: Pension and postretirement benefits (a) (e) $ 165,861 $ 165,898 Natural gas costs recoverable through rate adjustments (a) (b) Up to 3 years 94,543 42,652 Asset retirement obligations (a) Over plant lives 64,215 60,097 Cost recovery mechanisms (a) (b) Up to 4 years 18,488 17,948 Manufactured gas plant site remediation (a) - 15,619 17,068 Taxes recoverable from customers (a) Over plant lives 11,755 11,946 Plants to be retired (a) - 16,933 — Conservation programs (b) Up to 1 year 7,627 7,494 Long-term debt refinancing costs (a) Up to 19 years 4,592 4,898 Costs related to identifying generation development (a) Up to 8 years 2,280 2,508 Other (a) (b) Up to 20 years 5,761 9,608 Total regulatory assets $ 407,674 $ 340,117 Regulatory liabilities: Taxes refundable to customers (c) (d) $ 264,025 $ 277,833 Plant removal and decommissioning costs (c) (d) 175,003 173,143 Natural gas costs refundable through rate adjustments (d) 25,737 29,995 Pension and postretirement benefits (c) 12,967 15,264 Other (c) (d) 27,955 25,197 Total regulatory liabilities $ 505,687 $ 521,432 Net regulatory position $ (98,013 ) $ (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 June 30, 2019 and December 31, 2018 , approximately $290.5 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	6 Months Ended
	Jun. 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 $83.1 million , $78.3 million and $73.8 million , at June 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 $2.9 million and $9.3 million for the three and six months ended June 30, 2019 , respectively. The net unrealized gains on these investments were $1.4 million and $900,000 for the three and six months ended June 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: June 30, 2019 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,771 $ 94 $ 35 $ 10,830 U.S. Treasury securities 180 — — 180 Total $ 10,951 $ 94 $ 35 $ 11,010 June 30, 2018 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,015 $ 6 $ 236 $ 9,785 U.S. Treasury securities 242 — 2 240 Total $ 10,257 $ 6 $ 238 $ 10,025 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 six months ended June 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 June 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 June 30, 2019 (In thousands) Assets: Money market funds $ — $ 10,816 $ — $ 10,816 Insurance contract* — 83,134 — 83,134 Available-for-sale securities: Mortgage-backed securities — 10,830 — 10,830 U.S. Treasury securities — 180 — 180 Total assets measured at fair value $ — $ 104,960 $ — $ 104,960 * The insurance contract invests approximately 51 percent in fixed-income investments, 22 percent in common stock of large-cap companies, 12 percent in common stock of mid-cap companies, 10 percent in common stock of small-cap companies, 4 percent in target date investments and 1 percent in cash equivalents. Fair Value Measurements at June 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 June 30, 2018 (In thousands) Assets: Money market funds $ — $ 9,904 $ — $ 9,904 Insurance contract* — 78,312 — 78,312 Available-for-sale securities: Mortgage-backed securities — 9,785 — 9,785 U.S. Treasury securities — 240 — 240 Total assets measured at fair value $ — $ 98,241 $ — $ 98,241 * The insurance contract invests approximately 48 percent in fixed-income investments, 23 percent in common stock of large-cap companies, 13 percent in common stock of mid-cap companies, 11 percent in common stock of small-cap companies, 3 percent in target date investments and 2 percent in cash equivalents. Fair Value Measurements at December 31, 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 based on discounted future cash flows using current market interest rates. The estimated fair value of the Company's Level 2 long-term debt was as follows: Carrying Amount Fair Value (In thousands) Long-term debt at June 30, 2019 $ 2,379,806 $ 2,521,325 Long-term debt at June 30, 2018 $ 1,852,910 $ 1,949,564 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	6 Months Ended
	Jun. 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 June 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 six months ended June 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. Long-term debt The following describes certain transactions during the three and six months ended June 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 June 30, 2019 June 30, 2019 December 31, 2018 (In thousands) Senior notes due on dates ranging from July 1, 2019 to January 15, 2055 4.52 % $ 1,656,000 $ 1,381,000 Commercial paper supported by revolving credit agreements 2.77 % 433,350 338,100 Term loan agreements due on dates ranging from October 17, 2019 to September 3, 2032 2.75 % 209,800 209,800 Credit agreements due on June 7, 2024 5.50 % 11,075 110,100 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 January 2, 2022 to November 30, 2038 5.01 % 26,105 25,229 Less unamortized debt issuance costs 6,164 5,207 Less discount 360 327 Total long-term debt 2,379,806 2,108,695 Less current maturities 51,822 251,854 Net long-term debt $ 2,327,984 $ 1,856,841 Schedule of Debt Maturities Long-term debt maturities, which excludes unamortized debt issuance costs and discount, as of June 30, 2019 , were as follows: Remainder of 2019 2020 2021 2022 2023 Thereafter (In thousands) Long-term debt maturities $ 51,761 $ 15,926 $ 386,430 $ 147,434 $ 125,188 $ 1,659,591

Cash flow information

Cash flow information	6 Months Ended
	Jun. 30, 2019
Supplemental Cash Flow Information [Abstract]
Cash flow information	Cash flow information Cash expenditures for interest and income taxes were as follows: Six Months Ended June 30, 2019 2018 (In thousands) Interest, net* $ 45,702 $ 39,467 Income taxes paid, net** $ 4,124 $ 4,034 * AFUDC - borrowed was $1.2 million and $1.0 million for the six months ended June 30, 2019 and 2018 , respectively. ** Income taxes paid, net of discontinued operations, were $2.0 million and $3.1 million for the six months ended June 30, 2019 and 2018 , respectively. Noncash investing and financing transactions were as follows: June 30, 2019 June 30, 2018 December 31, 2018 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 24,990 $ — $ — Property, plant and equipment additions in accounts payable $ 27,312 $ 30,985 $ 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	6 Months Ended
	Jun. 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 Six Months Ended June 30, June 30, 2019 2018 2019 2018 (In thousands) External operating revenues: Regulated operations: Electric $ 81,011 $ 78,499 $ 173,578 $ 165,904 Natural gas distribution 133,867 129,540 476,014 462,204 Pipeline and midstream 21,369 18,645 26,272 23,035 236,247 226,684 675,864 651,143 Nonregulated operations: Pipeline and midstream 7,311 5,415 11,021 9,858 Construction materials and contracting 595,799 509,388 822,911 722,672 Construction services 464,192 323,020 884,925 657,071 Other 24 90 43 146 1,067,326 837,913 1,718,900 1,389,747 Total external operating revenues $ 1,303,573 $ 1,064,597 $ 2,394,764 $ 2,040,890 Three Months Ended Six Months Ended June 30, June 30, 2019 2018 2019 2018 (In thousands) Intersegment operating revenues: Regulated operations: Electric $ — $ — $ — $ — Natural gas distribution — — — — Pipeline and midstream 7,426 6,446 31,349 28,182 7,426 6,446 31,349 28,182 Nonregulated operations: Pipeline and midstream 87 93 119 116 Construction materials and contracting 168 235 264 336 Construction services 721 540 849 550 Other 2,879 2,667 10,704 5,306 3,855 3,535 11,936 6,308 Intersegment eliminations (11,281 ) (9,981 ) (43,285 ) (34,490 ) Total intersegment operating revenues $ — $ — $ — $ — Operating income (loss): Electric $ 9,791 $ 13,027 $ 27,779 $ 31,182 Natural gas distribution (2,621 ) (4,371 ) 47,696 44,169 Pipeline and midstream 10,698 8,482 20,602 16,650 Construction materials and contracting 46,178 37,301 4,597 10,992 Construction services 31,966 19,356 59,431 39,990 Other 1,299 197 1,425 385 Total operating income $ 97,311 $ 73,992 $ 161,530 $ 143,368 Net income (loss): Regulated operations: Electric $ 7,471 $ 9,133 $ 22,976 $ 22,216 Natural gas distribution (6,252 ) (6,852 ) 30,248 25,771 Pipeline and midstream 6,378 5,240 13,382 10,699 7,597 7,521 66,606 58,686 Nonregulated operations: Pipeline and midstream 742 467 579 288 Construction materials and contracting 29,166 24,336 (5,283 ) 815 Construction services 22,845 14,088 42,869 29,179 Other 2,795 (2,337 ) (537 ) (2,932 ) 55,548 36,554 37,628 27,350 Income from continuing operations 63,145 44,075 104,234 86,036 Income (loss) from discontinued operations, net of tax (1,320 ) (273 ) (1,483 ) 203 Net income $ 61,825 $ 43,802 $ 102,751 $ 86,239

Employee benefit plans

Employee benefit plans	6 Months Ended
	Jun. 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 June 30, 2019 2018 2019 2018 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 227 $ 340 Interest cost 3,840 3,488 713 672 Expected return on assets (3,998 ) (5,379 ) (1,182 ) (1,266 ) Amortization of prior service credit — — (228 ) (348 ) Amortization of net actuarial (gain) loss 1,418 1,721 (42 ) 82 Net periodic benefit cost (credit), including amount capitalized 1,260 (170 ) (512 ) (520 ) Less amount capitalized — — 27 43 Net periodic benefit cost (credit) $ 1,260 $ (170 ) $ (539 ) $ (563 ) Pension Benefits Other Postretirement Benefits Six Months Ended June 30, 2019 2018 2019 2018 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 571 $ 747 Interest cost 7,613 7,295 1,493 1,450 Expected return on assets (9,118 ) (10,377 ) (2,402 ) (2,433 ) Amortization of prior service credit — — (577 ) (697 ) Amortization of net actuarial loss 2,773 3,503 55 320 Net periodic benefit cost (credit), including amount capitalized 1,268 421 (860 ) (613 ) Less amount capitalized — — 58 83 Net periodic benefit cost (credit) $ 1,268 $ 421 $ (918 ) $ (696 ) 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 six months ended June 30, 2019 , was $1.1 million and $2.2 million , respectively. The Company's net periodic benefit cost for these plans for the three and six months ended June 30, 2018 , was $1.1 million and $2.2 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	6 Months Ended
	Jun. 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 , to be issued within 120 days of the implementation of new rates, for the period from January 1, 2018 through April 30, 2019. MTPSC On September 28, 2018, Montana-Dakota filed an application with the MTPSC for an electric rate increase of approximately $11.9 million annually or approximately 18.9 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. The requested increase was partially offset by tax savings related to the TCJA. On March 7, 2019, the MTPSC issued an interim order authorizing an interim increase of $7.9 million or approximately 12.8 percent, subject to refund, to be effective with service rendered on or after April 1, 2019. On April 24, 2019, Montana-Dakota submitted a settlement agreement reflecting a $9.0 million annual increase to be implemented in the first 12 months following the date of approval and an additional $300,000 annual increase to be implemented beginning 12 months after the date of approval. On June 18, 2019, the MTPSC voted to approve the settlement as filed. NDPSC On January 23, 2019, the NDPSC approved a $168,000 reduction in annual revenues for Great Plains to reflect TCJA impacts effective February 1, 2019, along with the refund plan that provided for approximately $200,000 in refunds that were credited to customers' bills on April 12, 2019. On July 19, 2019, Montana-Dakota filed an update with the NDPSC to recover approximately $1.5 million annually for the revenue requirements on certain electric transmission projects through its transmission cost adjustment rate. This matter is pending before the NDPSC. OPUC On December 29, 2017, Cascade filed a request with the OPUC to use deferral accounting for the 2018 net benefits associated with the implementation of the TCJA. The deferral request was renewed on December 28, 2018. This matter is pending before the OPUC. On May 31, 2018, Cascade filed a general rate case with the OPUC requesting an overall increase to Cascade's natural gas rates of approximately $2.3 million or 3.5 percent on an annual basis, which incorporated the impact of the TCJA. On January 22, 2019, Cascade filed a stipulation with the OPUC for an annual increase in revenues of $1.7 million with a $500,000 reduction for excess deferred income taxes, for a net increase of $1.2 million . On March 14, 2019, the OPUC approved the settlement with rates effective April 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 28, 2019, the WUTC approved an increase to Cascade's natural gas rates through an out-of-period purchased gas adjustment surcharge. The increase of approximately $48.0 million reflected unrecovered purchased gas costs from October 2018 through the end of January 2019 as a result of the rupture of the Enbridge pipeline in Canada on October 9, 2018, causing increased natural gas costs. The WUTC approved this amount, including interest, to be collected over three years beginning April 1, 2019. 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. This matter is pending before the WUTC. The WUTC has 11 months to process the request and issue an order. 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. This matter is pending before the WUTC. 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 July 16, 2019, the WYPSC ruled in a hearing for Montana-Dakota to provide for a one-time refund of approximately $190,000 to be credited to customers' bills by November 1, 2019, for the TCJA impacts from January 1, 2018 through June 30, 2019. This matter is pending before the WYPSC. 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. This matter is pending before the FERC.

Contingencies

Contingencies	6 Months Ended
	Jun. 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. The Company has accrued liabilities of $32.1 million , $31.1 million and $30.4 million , which have not been discounted, including liabilities held for sale, for contingencies, including litigation, production taxes, royalty claims and environmental matters at June 30, 2019 and 2018 , and December 31, 2018 , respectively. 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 There are three claims against Cascade for cleanup of environmental contamination at manufactured gas plant sites operated by Cascade's predecessors, and one against Montana-Dakota at a site operated by Montana-Dakota or its predecessors. Any accruals related to these claims are reflected in regulatory assets. For more information, see Note 13 . The first claim against Cascade is for contamination at a site in Eugene, Oregon, which was received in 1995. The Oregon DEQ released an ROD in January 2015 that selected a remediation alternative for the site as recommended in an earlier staff report. In the second quarter of 2019, site field work for the design was completed which resulted in reducing the total estimated cost for the selected remediation, including long-term maintenance, to approximately $2.4 million of which $400,000 has been incurred. Cascade and other PRPs are finalizing a proposed consent judgment with the Oregon DEQ by which the PRPs agree to perform the recommended remediation and long-term maintenance for the site. Cascade and other PRPs will share in the cleanup and maintenance costs with Cascade to pay 50 percent of such costs. Cascade has an accrual balance of $1.0 million for remediation and maintenance of this site. In January 2013, the OPUC approved Cascade's application to defer environmental remediation costs at the Eugene site for a period of 12 months starting November 30, 2012. Cascade received orders reauthorizing the deferred accounting. The second claim against Cascade is 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 $3.6 million has been incurred. Cascade has accrued $4.0 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. The third claim against Cascade is 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. 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 have tentatively 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. 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 June 30, 2019 , the fixed maximum amounts guaranteed under these agreements aggregated $274.2 million . The amounts of scheduled expiration of the maximum amounts guaranteed under these agreements aggregate to $85.5 million in 2019 ; $181.4 million in 2020 ; $700,000 in 2021 ; $500,000 in 2022 ; $500,000 in 2023 ; $1.6 million thereafter; and $4.0 million , which has no scheduled maturity date. There were no amounts outstanding under the above guarantees at June 30, 2019 . In the event of default under these guarantee obligations, the subsidiary issuing the guarantee for that particular obligation would be required to make payments under its guarantee. Certain subsidiaries have outstanding letters of credit to third parties related to insurance policies and other agreements, some of which are guaranteed by other subsidiaries of the Company. At June 30, 2019 , the fixed maximum amounts guaranteed under these letters of credit aggregated $32.8 million . The amounts of scheduled expiration of the maximum amounts guaranteed under these letters of credit aggregate to $29.4 million in 2019 and $3.4 million in 2020 . There were no amounts outstanding under the above letters of credit at June 30, 2019 . In the event of default under these letter of credit obligations, the subsidiary guaranteeing the letter of credit would be obligated for reimbursement of payments made under the letter of credit. In addition, Centennial, Knife River and MDU Construction Services have issued guarantees to third parties related to the routine purchase of maintenance items, materials and lease obligations for which no fixed maximum amounts have been specified. These guarantees have no scheduled maturity date. In the event a subsidiary of the Company defaults under these obligations, Centennial, Knife River or MDU Construction Services would be required to make payments under these guarantees. Any amounts outstanding by subsidiaries of the Company were reflected on the Consolidated Balance Sheet at June 30, 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 June 30, 2019 , approximately $1.1 billion of surety bonds were outstanding, which were not reflected on the Consolidated Balance Sheet. Variable interest entities The Company evaluates its arrangements and contracts with other entities to determine if they are VIEs and if so, if the Company is the primary beneficiary. Fuel Contract Coyote Station entered into a coal supply agreement with Coyote Creek that provides for the purchase of coal necessary to supply the coal requirements of the Coyote Station for the period May 2016 through December 2040. Coal purchased under the coal supply agreement is reflected in inventories on the 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 June 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 $37.3 million .

Basis of presentation (Policies

Basis of presentation (Policies)	6 Months Ended
	Jun. 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)	6 Months Ended
	Jun. 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)	6 Months Ended
	Jun. 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)	6 Months Ended
	Jun. 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)	6 Months Ended
	Jun. 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, and 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 does not expect the guidance to have a material impact on its results of operations, financial position, cash flows and 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 is evaluating the guidance and does not expect it to have a material impact on its results of operations, financial position, cash flows and disclosures. 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)	6 Months Ended
	Jun. 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)	6 Months Ended
	Jun. 30, 2019
Business Combinations [Abstract]
Business Combinations Policy [Policy Text Block]	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 construction materials and contracting segment and 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. However, 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)	6 Months Ended
	Jun. 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)	6 Months Ended
	Jun. 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)	6 Months Ended
	Jun. 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)	6 Months Ended
	Jun. 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)	6 Months Ended
	Jun. 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)	6 Months Ended
	Jun. 30, 2019
Inventory Disclosure [Abstract]
Inventories	Inventories on the Consolidated Balance Sheets were as follows: June 30, 2019 June 30, 2018 December 31, 2018 (In thousands) Aggregates held for resale $ 147,030 $ 131,784 $ 139,681 Asphalt oil 80,418 64,560 54,741 Materials and supplies 28,746 24,688 23,611 Merchandise for resale 27,167 17,502 22,552 Natural gas in storage (current) 15,841 13,774 22,117 Other 26,742 25,931 24,607 Total $ 325,944 $ 278,239 $ 287,309

Earnings per common share (Tabl

Earnings per common share (Tables)	6 Months Ended
	Jun. 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 Six Months Ended June 30, June 30, 2019 2018 2019 2018 (In thousands, except per share amounts) Weighted average common shares outstanding - basic 198,270 195,524 197,341 195,415 Effect of dilutive performance share awards and restricted stock units 17 645 15 662 Weighted average common shares outstanding - diluted 198,287 196,169 197,356 196,077 Shares excluded from the calculation of diluted earnings per share — — 93 — Dividends declared per common share $ .2025 $ .1975 $ .4050 $ .3950

Accumulated other comprehensi_2

Accumulated other comprehensive income (loss) (Tables)	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Accumulated comprehensive loss	The after-tax changes in the components of accumulated other comprehensive income (loss) were as follows: Six Months Ended June 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 ) Six Months Ended June 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 )
Reclassification out of accumulated other comprehensive loss	The following amounts were reclassified out of accumulated other comprehensive loss into net income. The amounts presented in parenthesis indicate a decrease to net income on the Consolidated Statements of Income. The reclassifications were as follows: Three Months Ended Six Months Ended Location on Consolidated Statements of Income June 30, June 30, 2019 2018 2019 2018 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income $ (147 ) $ (148 ) $ (295 ) $ (296 ) Interest expense 36 53 (213 ) 109 Income taxes (111 ) (95 ) (508 ) (187 ) Amortization of postretirement liability losses included in net periodic benefit cost (credit) (365 ) (594 ) (775 ) (1,167 ) Other income 89 145 189 300 Income taxes (276 ) (449 ) (586 ) (867 ) Reclassification adjustment for loss on foreign currency translation adjustment included in net income — (324 ) — (324 ) Other income — 75 — 75 Income taxes — (249 ) — (249 ) Reclassification adjustment on available-for-sale investments included in net income (15 ) (44 ) (50 ) (81 ) Other income 3 10 10 17 Income taxes (12 ) (34 ) (40 ) (64 ) Total reclassifications $ (399 ) $ (827 ) $ (1,134 ) $ (1,367 )

Revenue from contracts with c_3

Revenue from contracts with customers (Tables)	6 Months Ended
	Jun. 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 June 30, 2019 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 26,437 $ 71,010 $ — $ — $ — $ — $ 97,447 Commercial utility sales 33,231 41,250 — — — — 74,481 Industrial utility sales 9,344 5,577 — — — — 14,921 Other utility sales 1,879 — — — — — 1,879 Natural gas transportation — 10,706 24,804 — — — 35,510 Natural gas gathering — — 2,396 — — — 2,396 Natural gas storage — — 2,623 — — — 2,623 Contracting services — — — 297,124 — — 297,124 Construction materials — — — 444,768 — — 444,768 Intrasegment eliminations* — — — (145,925 ) — — (145,925 ) Inside specialty contracting — — — — 319,276 — 319,276 Outside specialty contracting — — — — 133,288 — 133,288 Other 8,417 2,923 6,293 — 9 2,903 20,545 Intersegment eliminations — — (7,513 ) (168 ) (721 ) (2,879 ) (11,281 ) Revenues from contracts with customers 79,308 131,466 28,603 595,799 451,852 24 1,287,052 Revenues out of scope 1,703 2,401 77 — 12,340 — 16,521 Total external operating revenues $ 81,011 $ 133,867 $ 28,680 $ 595,799 $ 464,192 $ 24 $ 1,303,573 * 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 June 30, 2018 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 26,752 $ 68,688 $ — $ — $ — $ — $ 95,440 Commercial utility sales 32,676 40,820 — — — — 73,496 Industrial utility sales 8,226 5,227 — — — — 13,453 Other utility sales 1,874 — — — — — 1,874 Natural gas transportation — 10,084 21,287 — — — 31,371 Natural gas gathering — — 2,310 — — — 2,310 Natural gas storage — — 2,634 — — — 2,634 Contracting services — — — 247,558 — — 247,558 Construction materials — — — 387,632 — — 387,632 Intrasegment eliminations* — — — (125,567 ) — — (125,567 ) Inside specialty contracting — — — — 216,371 — 216,371 Outside specialty contracting — — — — 95,261 — 95,261 Other 8,425 3,614 4,326 — 103 2,757 19,225 Intersegment eliminations — — (6,539 ) (235 ) (540 ) (2,667 ) (9,981 ) Revenues from contracts with customers 77,953 128,433 24,018 509,388 311,195 90 1,051,077 Revenues out of scope 546 1,107 42 — 11,825 — 13,520 Total external operating revenues $ 78,499 $ 129,540 $ 24,060 $ 509,388 $ 323,020 $ 90 $ 1,064,597 * 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. Six Months Ended June 30, 2019 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 62,993 $ 271,619 $ — $ — $ — $ — $ 334,612 Commercial utility sales 68,902 163,043 — — — — 231,945 Industrial utility sales 18,228 14,188 — — — — 32,416 Other utility sales 3,678 — — — — — 3,678 Natural gas transportation — 22,276 49,862 — — — 72,138 Natural gas gathering — — 4,517 — — — 4,517 Natural gas storage — — 5,269 — — — 5,269 Contracting services — — — 380,164 — — 380,164 Construction materials — — — 624,077 — — 624,077 Intrasegment eliminations* — — — (181,066 ) — — (181,066 ) Inside specialty contracting — — — — 618,805 — 618,805 Outside specialty contracting — — — — 240,686 — 240,686 Other 17,538 6,836 8,989 — 26 10,747 44,136 Intersegment eliminations — — (31,468 ) (264 ) (849 ) (10,704 ) (43,285 ) Revenues from contracts with customers 171,339 477,962 37,169 822,911 858,668 43 2,368,092 Revenues out of scope 2,239 (1,948 ) 124 — 26,257 — 26,672 Total external operating revenues $ 173,578 $ 476,014 $ 37,293 $ 822,911 $ 884,925 $ 43 $ 2,394,764 * 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. Six Months Ended June 30, 2018 Electric Natural gas distribution Pipeline and midstream Construction materials and contracting Construction services Other Total (In thousands) Residential utility sales $ 61,935 $ 261,574 $ — $ — $ — $ — $ 323,509 Commercial utility sales 67,377 157,711 — — — — 225,088 Industrial utility sales 16,996 13,036 — — — — 30,032 Other utility sales 3,710 — — — — — 3,710 Natural gas transportation — 21,263 43,105 — — — 64,368 Natural gas gathering — — 4,580 — — — 4,580 Natural gas storage — — 5,768 — — — 5,768 Contracting services — — — 321,622 — — 321,622 Construction materials — — — 561,223 — — 561,223 Intrasegment eliminations* — — — (159,837 ) — — (159,837 ) Inside specialty contracting — — — — 450,192 — 450,192 Outside specialty contracting — — — — 182,442 — 182,442 Other 16,678 7,613 7,652 — 17 5,452 37,412 Intersegment eliminations — — (28,298 ) (336 ) (550 ) (5,306 ) (34,490 ) Revenues from contracts with customers 166,696 461,197 32,807 722,672 632,101 146 2,015,619 Revenues out of scope (792 ) 1,007 86 — 24,970 — 25,271 Total external operating revenues $ 165,904 $ 462,204 $ 32,893 $ 722,672 $ 657,071 $ 146 $ 2,040,890 * 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: June 30, 2019 December 31, 2018 Change Location on Consolidated Balance Sheets (In thousands) Contract assets $ 153,641 $ 104,239 $ 49,402 Receivables, net Contract liabilities - current (90,031 ) (93,901 ) 3,870 Accounts payable Contract liabilities - noncurrent (25 ) (135 ) 110 Deferred credits and other liabilities - other Net contract assets $ 63,585 $ 10,203 $ 53,382

Discontinued operations (Tables

Discontinued operations (Tables)	6 Months Ended
	Jun. 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: June 30, 2019 June 30, 2018 December 31, 2018 (In thousands) Assets Current assets: Receivables, net $ 428 $ 572 $ 430 Income taxes receivable (a) — 1,689 — Total current assets held for sale 428 2,261 430 Noncurrent assets: Net property, plant and equipment — 1,236 — Deferred income taxes 1,926 2,637 1,926 Other 161 162 161 Total noncurrent assets held for sale 2,087 4,035 2,087 Total assets held for sale $ 2,515 $ 6,296 $ 2,517 Liabilities Current liabilities: Accounts payable $ 82 $ — $ 80 Taxes payable 3,114 10,656 1,451 Other accrued liabilities 3,021 2,746 2,470 Total current liabilities held for sale 6,217 13,402 4,001 Noncurrent liabilities: Deferred income taxes (b) — 37 — Total noncurrent liabilities held for sale — 37 — Total liabilities held for sale $ 6,217 $ 13,439 $ 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 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 Six Months Ended June 30, June 30, 2019 2018 2019 2018 (In thousands) Operating revenues $ 37 $ 75 $ 67 $ 140 Operating expenses 1,778 435 2,023 609 Operating loss (1,741 ) (360 ) (1,956 ) (469 ) Other income — — — 12 Interest expense — — — 575 Loss from discontinued operations before income taxes (1,741 ) (360 ) (1,956 ) (1,032 ) Income taxes (421 ) (87 ) (473 ) (1,235 ) Income (loss) from discontinued operations $ (1,320 ) $ (273 ) $ (1,483 ) $ 203

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Lease, Cost [Table Text Block]	The following tables provide information on the Company's operating leases: Three Months Ended Six Months Ended June 30, June 30, 2019 2019 (In thousands) Lease costs: Operating lease cost $ 10,387 $ 21,908 Variable lease cost 400 799 Short-term lease cost 40,474 57,712 Total lease costs $ 51,261 $ 80,419 June 30, 2019 (Dollars in thousands) Weighted average remaining lease term 3.02 years Weighted average discount rate 4.46 % Cash paid for amounts included in the measurement of lease liabilities $ 21,798
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 is as follows: June 30, 2019 (In thousands) Remainder of 2019 $ 19,276 2020 30,065 2021 22,850 2022 14,816 2023 8,941 Thereafter 51,335 Total 147,283 Less discount 28,496 Total operating lease liabilities $ 118,787 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)	6 Months Ended
	Jun. 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: Six Months Ended June 30, 2019 Balance at January 1, 2019 Goodwill Acquired the Year Balance at June 30, 2019 (In thousands) Natural gas distribution $ 345,736 $ — $ 345,736 Construction materials and contracting 209,421 14,473 223,894 Construction services 109,765 — 109,765 Total $ 664,922 $ 14,473 $ 679,395 Six Months Ended June 30, 2018 Balance at January 1, 2018 Goodwill Acquired the Year Balance at June 30, 2018 (In thousands) Natural gas distribution $ 345,736 $ — $ 345,736 Construction materials and contracting 176,290 10,583 186,873 Construction services 109,765 — 109,765 Total $ 631,791 $ 10,583 $ 642,374 Year Ended December 31, 2018 Balance at January 1, 2018 Goodwill Acquired the Year 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: June 30, 2019 June 30, 2018 December 31, 2018 (In thousands) Customer relationships $ 14,601 $ 15,587 $ 22,720 Less accumulated amortization 5,629 13,191 13,535 8,972 2,396 9,185 Noncompete agreements 3,179 2,546 2,605 Less accumulated amortization 1,798 1,877 1,956 1,381 669 649 Other 6,578 6,458 6,458 Less accumulated amortization 5,608 5,333 5,477 970 1,125 981 Total $ 11,323 $ 4,190 $ 10,815
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	Estimated amortization expense for identifiable intangible assets as of June 30, 2019 , was: Remainder of 2019 2020 2021 2022 2023 Thereafter (In thousands) Amortization expense $ 938 $ 1,644 $ 1,254 $ 1,231 $ 1,249 $ 5,007

Regulatory assets and liabili_2

Regulatory assets and liabilities (Tables)	6 Months Ended
	Jun. 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 * June 30, 2019 December 31, 2018 (In thousands) Regulatory assets: Pension and postretirement benefits (a) (e) $ 165,861 $ 165,898 Natural gas costs recoverable through rate adjustments (a) (b) Up to 3 years 94,543 42,652 Asset retirement obligations (a) Over plant lives 64,215 60,097 Cost recovery mechanisms (a) (b) Up to 4 years 18,488 17,948 Manufactured gas plant site remediation (a) - 15,619 17,068 Taxes recoverable from customers (a) Over plant lives 11,755 11,946 Plants to be retired (a) - 16,933 — Conservation programs (b) Up to 1 year 7,627 7,494 Long-term debt refinancing costs (a) Up to 19 years 4,592 4,898 Costs related to identifying generation development (a) Up to 8 years 2,280 2,508 Other (a) (b) Up to 20 years 5,761 9,608 Total regulatory assets $ 407,674 $ 340,117 Regulatory liabilities: Taxes refundable to customers (c) (d) $ 264,025 $ 277,833 Plant removal and decommissioning costs (c) (d) 175,003 173,143 Natural gas costs refundable through rate adjustments (d) 25,737 29,995 Pension and postretirement benefits (c) 12,967 15,264 Other (c) (d) 27,955 25,197 Total regulatory liabilities $ 505,687 $ 521,432 Net regulatory position $ (98,013 ) $ (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 * June 30, 2019 December 31, 2018 (In thousands) Regulatory assets: Pension and postretirement benefits (a) (e) $ 165,861 $ 165,898 Natural gas costs recoverable through rate adjustments (a) (b) Up to 3 years 94,543 42,652 Asset retirement obligations (a) Over plant lives 64,215 60,097 Cost recovery mechanisms (a) (b) Up to 4 years 18,488 17,948 Manufactured gas plant site remediation (a) - 15,619 17,068 Taxes recoverable from customers (a) Over plant lives 11,755 11,946 Plants to be retired (a) - 16,933 — Conservation programs (b) Up to 1 year 7,627 7,494 Long-term debt refinancing costs (a) Up to 19 years 4,592 4,898 Costs related to identifying generation development (a) Up to 8 years 2,280 2,508 Other (a) (b) Up to 20 years 5,761 9,608 Total regulatory assets $ 407,674 $ 340,117 Regulatory liabilities: Taxes refundable to customers (c) (d) $ 264,025 $ 277,833 Plant removal and decommissioning costs (c) (d) 175,003 173,143 Natural gas costs refundable through rate adjustments (d) 25,737 29,995 Pension and postretirement benefits (c) 12,967 15,264 Other (c) (d) 27,955 25,197 Total regulatory liabilities $ 505,687 $ 521,432 Net regulatory position $ (98,013 ) $ (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)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Available-for-sale securities	Details of available-for-sale securities were as follows: June 30, 2019 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,771 $ 94 $ 35 $ 10,830 U.S. Treasury securities 180 — — 180 Total $ 10,951 $ 94 $ 35 $ 11,010 June 30, 2018 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,015 $ 6 $ 236 $ 9,785 U.S. Treasury securities 242 — 2 240 Total $ 10,257 $ 6 $ 238 $ 10,025 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 June 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 June 30, 2019 (In thousands) Assets: Money market funds $ — $ 10,816 $ — $ 10,816 Insurance contract* — 83,134 — 83,134 Available-for-sale securities: Mortgage-backed securities — 10,830 — 10,830 U.S. Treasury securities — 180 — 180 Total assets measured at fair value $ — $ 104,960 $ — $ 104,960 * The insurance contract invests approximately 51 percent in fixed-income investments, 22 percent in common stock of large-cap companies, 12 percent in common stock of mid-cap companies, 10 percent in common stock of small-cap companies, 4 percent in target date investments and 1 percent in cash equivalents. Fair Value Measurements at June 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 June 30, 2018 (In thousands) Assets: Money market funds $ — $ 9,904 $ — $ 9,904 Insurance contract* — 78,312 — 78,312 Available-for-sale securities: Mortgage-backed securities — 9,785 — 9,785 U.S. Treasury securities — 240 — 240 Total assets measured at fair value $ — $ 98,241 $ — $ 98,241 * The insurance contract invests approximately 48 percent in fixed-income investments, 23 percent in common stock of large-cap companies, 13 percent in common stock of mid-cap companies, 11 percent in common stock of small-cap companies, 3 percent in target date investments and 2 percent in cash equivalents. Fair Value Measurements at December 31, 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 Level 2 long-term debt was as follows: Carrying Amount Fair Value (In thousands) Long-term debt at June 30, 2019 $ 2,379,806 $ 2,521,325 Long-term debt at June 30, 2018 $ 1,852,910 $ 1,949,564 Long-term debt at December 31, 2018 $ 2,108,695 $ 2,183,819

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2019
Debt Disclosure [Abstract]
Long-term debt outstanding	Long-term debt outstanding was as follows: Weighted Average Interest Rate at June 30, 2019 June 30, 2019 December 31, 2018 (In thousands) Senior notes due on dates ranging from July 1, 2019 to January 15, 2055 4.52 % $ 1,656,000 $ 1,381,000 Commercial paper supported by revolving credit agreements 2.77 % 433,350 338,100 Term loan agreements due on dates ranging from October 17, 2019 to September 3, 2032 2.75 % 209,800 209,800 Credit agreements due on June 7, 2024 5.50 % 11,075 110,100 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 January 2, 2022 to November 30, 2038 5.01 % 26,105 25,229 Less unamortized debt issuance costs 6,164 5,207 Less discount 360 327 Total long-term debt 2,379,806 2,108,695 Less current maturities 51,822 251,854 Net long-term debt $ 2,327,984 $ 1,856,841
Schedule of debt maturities	Long-term debt maturities, which excludes unamortized debt issuance costs and discount, as of June 30, 2019 , were as follows: Remainder of 2019 2020 2021 2022 2023 Thereafter (In thousands) Long-term debt maturities $ 51,761 $ 15,926 $ 386,430 $ 147,434 $ 125,188 $ 1,659,591

Cash flow information (Tables)

Cash flow information (Tables)	6 Months Ended
	Jun. 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: Six Months Ended June 30, 2019 2018 (In thousands) Interest, net* $ 45,702 $ 39,467 Income taxes paid, net** $ 4,124 $ 4,034 * AFUDC - borrowed was $1.2 million and $1.0 million for the six months ended June 30, 2019 and 2018 , respectively. ** Income taxes paid, net of discontinued operations, were $2.0 million and $3.1 million for the six months ended June 30, 2019 and 2018 , respectively. Noncash investing and financing transactions were as follows: June 30, 2019 June 30, 2018 December 31, 2018 (In thousands) Right-of-use assets obtained in exchange for new operating lease liabilities $ 24,990 $ — $ — Property, plant and equipment additions in accounts payable $ 27,312 $ 30,985 $ 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)	6 Months Ended
	Jun. 30, 2019
Segment Reporting [Abstract]
Information on the Company's businesses	Information on the Company's segments was as follows: Three Months Ended Six Months Ended June 30, June 30, 2019 2018 2019 2018 (In thousands) External operating revenues: Regulated operations: Electric $ 81,011 $ 78,499 $ 173,578 $ 165,904 Natural gas distribution 133,867 129,540 476,014 462,204 Pipeline and midstream 21,369 18,645 26,272 23,035 236,247 226,684 675,864 651,143 Nonregulated operations: Pipeline and midstream 7,311 5,415 11,021 9,858 Construction materials and contracting 595,799 509,388 822,911 722,672 Construction services 464,192 323,020 884,925 657,071 Other 24 90 43 146 1,067,326 837,913 1,718,900 1,389,747 Total external operating revenues $ 1,303,573 $ 1,064,597 $ 2,394,764 $ 2,040,890 Three Months Ended Six Months Ended June 30, June 30, 2019 2018 2019 2018 (In thousands) Intersegment operating revenues: Regulated operations: Electric $ — $ — $ — $ — Natural gas distribution — — — — Pipeline and midstream 7,426 6,446 31,349 28,182 7,426 6,446 31,349 28,182 Nonregulated operations: Pipeline and midstream 87 93 119 116 Construction materials and contracting 168 235 264 336 Construction services 721 540 849 550 Other 2,879 2,667 10,704 5,306 3,855 3,535 11,936 6,308 Intersegment eliminations (11,281 ) (9,981 ) (43,285 ) (34,490 ) Total intersegment operating revenues $ — $ — $ — $ — Operating income (loss): Electric $ 9,791 $ 13,027 $ 27,779 $ 31,182 Natural gas distribution (2,621 ) (4,371 ) 47,696 44,169 Pipeline and midstream 10,698 8,482 20,602 16,650 Construction materials and contracting 46,178 37,301 4,597 10,992 Construction services 31,966 19,356 59,431 39,990 Other 1,299 197 1,425 385 Total operating income $ 97,311 $ 73,992 $ 161,530 $ 143,368 Net income (loss): Regulated operations: Electric $ 7,471 $ 9,133 $ 22,976 $ 22,216 Natural gas distribution (6,252 ) (6,852 ) 30,248 25,771 Pipeline and midstream 6,378 5,240 13,382 10,699 7,597 7,521 66,606 58,686 Nonregulated operations: Pipeline and midstream 742 467 579 288 Construction materials and contracting 29,166 24,336 (5,283 ) 815 Construction services 22,845 14,088 42,869 29,179 Other 2,795 (2,337 ) (537 ) (2,932 ) 55,548 36,554 37,628 27,350 Income from continuing operations 63,145 44,075 104,234 86,036 Income (loss) from discontinued operations, net of tax (1,320 ) (273 ) (1,483 ) 203 Net income $ 61,825 $ 43,802 $ 102,751 $ 86,239

Employee benefit plans (Tables)

Employee benefit plans (Tables)	6 Months Ended
	Jun. 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 June 30, 2019 2018 2019 2018 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 227 $ 340 Interest cost 3,840 3,488 713 672 Expected return on assets (3,998 ) (5,379 ) (1,182 ) (1,266 ) Amortization of prior service credit — — (228 ) (348 ) Amortization of net actuarial (gain) loss 1,418 1,721 (42 ) 82 Net periodic benefit cost (credit), including amount capitalized 1,260 (170 ) (512 ) (520 ) Less amount capitalized — — 27 43 Net periodic benefit cost (credit) $ 1,260 $ (170 ) $ (539 ) $ (563 ) Pension Benefits Other Postretirement Benefits Six Months Ended June 30, 2019 2018 2019 2018 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 571 $ 747 Interest cost 7,613 7,295 1,493 1,450 Expected return on assets (9,118 ) (10,377 ) (2,402 ) (2,433 ) Amortization of prior service credit — — (577 ) (697 ) Amortization of net actuarial loss 2,773 3,503 55 320 Net periodic benefit cost (credit), including amount capitalized 1,268 421 (860 ) (613 ) Less amount capitalized — — 58 83 Net periodic benefit cost (credit) $ 1,268 $ 421 $ (918 ) $ (696 )

Accounts receivable and allow_3

Accounts receivable and allowance for doubtful accounts (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Receivables [Abstract]
Receivables past due 90 days or more	$ 47.2	$ 30	$ 36.6
Allowance for doubtful accounts receivable	$ 8.2	$ 8.9	$ 7.8

Inventories and natural gas i_4

Inventories and natural gas in storage (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Inventory Disclosure [Abstract]
Aggregates held for resale	$ 147,030	$ 139,681	$ 131,784
Asphalt oil	80,418	54,741	64,560
Materials and supplies	28,746	23,611	24,688
Merchandise for resale	27,167	22,552	17,502
Natural gas in storage (current)	15,841	22,117	13,774
Other	26,742	24,607	25,931
Total	325,944	287,309	278,239
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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	198,270	195,524	197,341	195,415
Effect of dilutive performance share awards and restricted stock units	17	645	15	662
Weighted average common shares outstanding - diluted	198,287	196,169	197,356	196,077
Shares excluded from the calculation of diluted earnings per share	0	0	93	0
Dividends declared per common share	$ 0.2025	$ 0.1975	$ 0.4050	$ 0.3950

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				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	$ 2,605,692	$ 2,566,775	$ 2,426,111	$ 2,429,043	$ 2,566,775	$ 2,429,043
Other comprehensive income	478	774	725	433	1,252	1,158
Balance	2,660,301	2,605,692	2,451,078	2,426,111	2,660,301	2,451,078
Net unrealized gain (loss) on derivative instruments qualifying as hedges
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(1,764)	(2,161)	(2,231)	(1,934)	(2,161)	(1,934)
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive loss	111	397	95	92
Other comprehensive income	111	397	95	92
Balance	(1,653)	(1,764)	(2,136)	(2,231)	(1,653)	(2,136)
Postretirement liability adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(35,759)	(36,069)	(42,265)	(35,163)	(36,069)	(35,163)
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive loss	276	310	449	418
Other comprehensive income	276	310	449	418
Balance	(35,483)	(35,759)	(41,816)	(42,265)	(35,483)	(41,816)
Foreign currency translation adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Balance			(190)	(155)		(155)
Other comprehensive income before reclassifications			(59)	(2)
Amounts reclassified from accumulated other comprehensive loss			249	0
Other comprehensive income			190	(2)
Balance			0	(190)		0
Net unrealized gain (loss) on available-for-sale investments
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(45)	(112)	(174)	(82)	(112)	(82)
Other comprehensive income before reclassifications	79	39	(43)	(105)
Amounts reclassified from accumulated other comprehensive loss	12	28	34	30
Other comprehensive income	91	67	(9)	(75)
Balance	46	(45)	(183)	(174)	46	(183)
Total accumulated other comprehensive loss
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(37,568)	(38,342)	(44,860)	(37,334)	(38,342)	(37,334)
Other comprehensive income before reclassifications	79	39	(102)	(107)
Amounts reclassified from accumulated other comprehensive loss	399	735	827	540
Other comprehensive income	478	774	725	433
Balance	$ (37,090)	$ (37,568)	$ (44,135)	(44,860)	$ (37,090)	$ (44,135)
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				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Interest expense	$ (25,429)		$ (20,800)		$ (48,836)	$ (41,246)
Income taxes	(10,352)		(10,716)		(17,668)	(18,267)
Other income	1,615		1,599		9,208	2,181
Net Income	61,825	$ 40,926	43,802	$ 42,437	102,751	86,239
Reclassification out of accumulated other comprehensive income
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Net Income	(399)		(827)		(1,134)	(1,367)
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	(147)		(148)		(295)	(296)
Income taxes	36		53		(213)	109
Net Income	(111)		(95)		(508)	(187)
Amortization of postretirement liability losses included in net periodic benefit cost (credit) | Reclassification out of accumulated other comprehensive income
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Income taxes	89		145		189	300
Other income	(365)		(594)		(775)	(1,167)
Net Income	(276)		(449)		(586)	(867)
Reclassification adjustment for loss on 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		75		0	75
Other income	0		(324)		0	(324)
Net Income	0		(249)		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	3		10		10	17
Other income	(15)		(44)		(50)	(81)
Net Income	$ (12)		$ (34)		$ (40)	$ (64)

Disaggregation of revenue (Deta

Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 1,303,573	$ 1,064,597	$ 2,394,764	$ 2,040,890
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(11,281)	(9,981)	(43,285)	(34,490)
Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(145,925)	(125,567)	(181,066)	(159,837)
Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues	35,510	31,371	72,138	64,368
Natural gas gathering
Disaggregation of Revenue [Line Items]
Revenues	2,396	2,310	4,517	4,580
Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues	2,623	2,634	5,269	5,768
Contracting services
Disaggregation of Revenue [Line Items]
Revenues	297,124	247,558	380,164	321,622
Construction materials
Disaggregation of Revenue [Line Items]
Revenues	444,768	387,632	624,077	561,223
Inside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	319,276	216,371	618,805	450,192
Outside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	133,288	95,261	240,686	182,442
Other
Disaggregation of Revenue [Line Items]
Revenues	20,545	19,225	44,136	37,412
Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	1,287,052	1,051,077	2,368,092	2,015,619
Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	16,521	13,520	26,672	25,271
Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	97,447	95,440	334,612	323,509
Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	74,481	73,496	231,945	225,088
Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	14,921	13,453	32,416	30,032
Other utility sales
Disaggregation of Revenue [Line Items]
Revenues	1,879	1,874	3,678	3,710
Electric
Disaggregation of Revenue [Line Items]
Revenues	81,011	78,499	173,578	165,904
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	8,417	8,425	17,538	16,678
Electric | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	79,308	77,953	171,339	166,696
Electric | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	1,703	546	2,239	(792)
Electric | Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	26,437	26,752	62,993	61,935
Electric | Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	33,231	32,676	68,902	67,377
Electric | Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	9,344	8,226	18,228	16,996
Electric | Other utility sales
Disaggregation of Revenue [Line Items]
Revenues	1,879	1,874	3,678	3,710
Natural gas distribution
Disaggregation of Revenue [Line Items]
Revenues	133,867	129,540	476,014	462,204
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	10,706	10,084	22,276	21,263
Natural gas distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	2,923	3,614	6,836	7,613
Natural gas distribution | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	131,466	128,433	477,962	461,197
Natural gas distribution | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	2,401	1,107	(1,948)	1,007
Natural gas distribution | Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	71,010	68,688	271,619	261,574
Natural gas distribution | Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	41,250	40,820	163,043	157,711
Natural gas distribution | Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	5,577	5,227	14,188	13,036
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	28,680	24,060	37,293	32,893
Pipeline and midstream | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(7,513)	(6,539)	(31,468)	(28,298)
Pipeline and midstream | Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues	24,804	21,287	49,862	43,105
Pipeline and midstream | Natural gas gathering
Disaggregation of Revenue [Line Items]
Revenues	2,396	2,310	4,517	4,580
Pipeline and midstream | Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues	2,623	2,634	5,269	5,768
Pipeline and midstream | Other
Disaggregation of Revenue [Line Items]
Revenues	6,293	4,326	8,989	7,652
Pipeline and midstream | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	28,603	24,018	37,169	32,807
Pipeline and midstream | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	77	42	124	86
Construction materials and contracting
Disaggregation of Revenue [Line Items]
Revenues	595,799	509,388	822,911	722,672
Construction materials and contracting | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(168)	(235)	(264)	(336)
Construction materials and contracting | Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(145,925)	(125,567)	(181,066)	(159,837)
Construction materials and contracting | Contracting services
Disaggregation of Revenue [Line Items]
Revenues	297,124	247,558	380,164	321,622
Construction materials and contracting | Construction materials
Disaggregation of Revenue [Line Items]
Revenues	444,768	387,632	624,077	561,223
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	595,799	509,388	822,911	722,672
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	464,192	323,020	884,925	657,071
Construction services | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(721)	(540)	(849)	(550)
Construction services | Inside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	319,276	216,371	618,805	450,192
Construction services | Outside specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	133,288	95,261	240,686	182,442
Construction services | Other
Disaggregation of Revenue [Line Items]
Revenues	9	103	26	17
Construction services | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	451,852	311,195	858,668	632,101
Construction services | Revenues out of scope
Disaggregation of Revenue [Line Items]
Revenues	12,340	11,825	26,257	24,970
Other
Disaggregation of Revenue [Line Items]
Revenues	24	90	43	146
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues	(2,879)	(2,667)	(10,704)	(5,306)
Other | Other
Disaggregation of Revenue [Line Items]
Revenues	2,903	2,757	10,747	5,452
Other | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	24	90	43	146
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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract assets	$ 153,641		$ 153,641		$ 104,239
Change in contract assets			49,402
Contract liabilities - current	(90,031)		(90,031)		(93,901)
Change in contract liabilities - current			3,870
Contract liabilities - noncurrent	(25)		(25)		(135)
Change in contract liabilities - noncurrent			110
Net contract assets	63,585		63,585		$ 10,203
Change in net contract assets			53,382
Amounts included in contract liability at the beginning of the period	22,600	$ 16,900	79,000	$ 68,900
Amounts from performance obligations satisfied in prior periods	$ 20,600	$ 2,600	$ 32,500	$ 5,300

Revenue from contracts with c_4

Revenue from contracts with customers Remaining performance obligations (Details 3) $ in Millions	Jun. 30, 2019USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 1,800
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	269.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	248.6
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	$ 2,300

Business Combinations (Details)

Business Combinations (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Business Combinations [Abstract]
Payments to Acquire Businesses, Gross	$ 32.1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	$ 1.2

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	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Current assets:
Total current assets held for sale	$ 428	$ 430	$ 572
Noncurrent assets:
Total noncurrent assets held for sale	2,087	2,087	3,998
Current liabilities:
Total current liabilities held for sale	6,217	4,001	11,713
Discontinued operations, held-for-sale or disposed of by sale
Current assets:
Receivables, net	428	430	572
Income taxes receivable (a)	0	0	1,689
Total current assets held for sale	428	430	2,261
Noncurrent assets:
Net property, plant and equipment	0	0	1,236
Deferred income taxes	1,926	1,926	2,637
Other	161	161	162
Total noncurrent assets held for sale	2,087	2,087	4,035
Total assets held for sale	2,515	2,517	6,296
Current liabilities:
Accounts payable	82	80	0
Taxes payable	3,114	1,451	10,656
Other accrued liabilities	3,021	2,470	2,746
Total current liabilities held for sale	6,217	4,001	13,402
Noncurrent liabilities:
Deferred income taxes (b)	0	0	37
Total noncurrent liabilities held for sale	0	0	37
Total liabilities held for sale	$ 6,217	$ 4,001	$ 13,439

Reconciliation of income and ex

Reconciliation of income and expenses (Details 3) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations	$ (1,320)	$ (273)	$ (1,483)	$ 203
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	37	75	67	140
Operating expenses	1,778	435	2,023	609
Operating loss	(1,741)	(360)	(1,956)	(469)
Other income	0	0	0	12
Interest expense	0	0	0	575
Loss from discontinued operations before income taxes	(1,741)	(360)	(1,956)	(1,032)
Income taxes	(421)	(87)	(473)	(1,235)
Income (loss) from discontinued operations	$ (1,320)	$ (273)	$ (1,483)	$ 203

Lease costs (Details)

Lease costs (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2019USD ($)
Leases [Abstract]
Operating lease cost	$ 10,387	$ 21,908
Variable lease cost	400	799
Short-term lease cost	40,474	57,712
Total lease costs	$ 51,261	$ 80,419
Weighted average remaining lease term	3 years 7 days	3 years 7 days
Weighted average discount rate	4.46%	4.46%
Cash paid for amounts included in the measurement of lease liabilities		$ 21,798

Operating lease liabilities und

Operating lease liabilities undiscounted cash flows maturity schedule (Details 2) $ in Thousands	Jun. 30, 2019USD ($)
Leases [Abstract]
Remainder of 2019	$ 19,276
2020	30,065
2021	22,850
2022	14,816
2023	8,941
Thereafter	51,335
Total	147,283
Less discount	28,496
Total operating lease liabilities	$ 118,787

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	6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2019USD ($)
Leases [Abstract]
Operating Lease, Lease Income	$ 12.5	$ 26.5
Lessor, Operating Lease, Payments to be Received, Next Twelve Months	$ 10.6	$ 10.6

Goodwill rollforward (Details)

Goodwill rollforward (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Goodwill [Roll Forward]
Balance at beginning of period	$ 664,922	$ 631,791	$ 631,791
Goodwill acquired during the year	14,473	10,583	33,131
Balance at end of period	679,395	642,374	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
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	10,583	33,131
Balance at end of period	223,894	186,873	209,421
Construction services
Goodwill [Roll Forward]
Balance at beginning of period	109,765	109,765	109,765
Goodwill acquired during the year	0	0	0
Balance at end of period	$ 109,765	$ 109,765	$ 109,765

Other intangible assets (Detail

Other intangible assets (Details 2) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 11,323,000	$ 4,190,000	$ 11,323,000	$ 4,190,000	$ 10,815,000
Amortization of intangible assets	500,000	300,000	1,100,000	700,000
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	14,601,000	15,587,000	14,601,000	15,587,000	22,720,000
Intangible assets, less accumulated amortization	5,629,000	13,191,000	5,629,000	13,191,000	13,535,000
Intangible assets, net (excluding goodwill)	8,972,000	2,396,000	8,972,000	2,396,000	9,185,000
Noncompete agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	3,179,000	2,546,000	3,179,000	2,546,000	2,605,000
Intangible assets, less accumulated amortization	1,798,000	1,877,000	1,798,000	1,877,000	1,956,000
Intangible assets, net (excluding goodwill)	1,381,000	669,000	1,381,000	669,000	649,000
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	6,578,000	6,458,000	6,578,000	6,458,000	6,458,000
Intangible assets, less accumulated amortization	5,608,000	5,333,000	5,608,000	5,333,000	5,477,000
Intangible assets, net (excluding goodwill)	$ 970,000	$ 1,125,000	970,000	$ 1,125,000	$ 981,000
Construction materials and contracting [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired			$ 1,600,000

Goodwill and other intangible_3

Goodwill and other intangible assets Future amortization expense (Details 3) $ in Thousands	Jun. 30, 2019USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2019	$ 938
2020	1,644
2021	1,254
2022	1,231
2023	1,249
Thereafter	$ 5,007

Regulatory assets and liabili_3

Regulatory assets and liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Regulatory Assets and Liabilities
Regulatory Assets	$ 407,674	$ 340,117
Regulatory Liabilities	505,687	521,432
Net Regulatory Position	(98,013)	(181,315)
Regulatory assets not earning a rate of return	290,500	313,500
Taxes recoverable from/refundable to customers
Regulatory Assets and Liabilities
Regulatory Liabilities	264,025	277,833
Plant removal
Regulatory Assets and Liabilities
Regulatory Liabilities	175,003	173,143
Natural gas costs refundable through rate adjustments
Regulatory Assets and Liabilities
Regulatory Liabilities	25,737	29,995
Pension and postretirement benefits
Regulatory Assets and Liabilities
Regulatory Liabilities	12,967	15,264
Other Regulatory Assets/Liabilities
Regulatory Assets and Liabilities
Regulatory Liabilities	$ 27,955	25,197
Pension and postretirement benefits
Regulatory Assets and Liabilities
Estimated Recovery Period	(e)
Regulatory Assets	$ 165,861	165,898
Natural gas costs recoverable through rate adjustments
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 3 years
Regulatory Assets	$ 94,543	42,652
Asset Retirement Obligation Costs
Regulatory Assets and Liabilities
Estimated Recovery Period	Over plant lives
Regulatory Assets	$ 64,215	60,097
Cost recovery mechanisms
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 4 years
Regulatory Assets	$ 18,488	17,948
Manufactured gas plant site remediation
Regulatory Assets and Liabilities
Estimated Recovery Period	-
Regulatory Assets	$ 15,619	17,068
Taxes recoverable from/refundable to customers
Regulatory Assets and Liabilities
Estimated Recovery Period	Over plant lives
Regulatory Assets	$ 11,755	11,946
Plant removal
Regulatory Assets and Liabilities
Estimated Recovery Period	-
Regulatory Assets	$ 16,933	0
Conservation programs
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 1 year
Regulatory Assets	$ 7,627	7,494
Long-term debt refinancing costs
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 19 years
Regulatory Assets	$ 4,592	4,898
Costs related to identifying generation development
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 8 years
Regulatory Assets	$ 2,280	2,508
Other Regulatory Assets/Liabilities
Regulatory Assets and Liabilities
Estimated Recovery Period	Up to 20 years
Regulatory Assets	$ 5,761	$ 9,608

Fair value measurements Insuran

Fair value measurements Insurance contracts (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Investments used to satisfy nonqualified benefit plans obligations	$ 83,100,000	$ 78,300,000	$ 83,100,000	$ 78,300,000	$ 73,800,000
Net unrealized gain (loss) on investments used to satisfy obligations under nonqualified benefit plans	$ 2,900,000	$ 1,400,000	$ 9,300,000	$ 900,000

Available-for-sale securities (

Available-for-sale securities (Details 2) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Available-for-sale securities [Abstract]
Cost	$ 10,951	$ 10,652	$ 10,257
Gross Unrealized Gains	94	21	6
Gross Unrealized Losses	35	162	238
Fair Value	11,010	10,511	10,025
Mortgage-backed securities
Available-for-sale securities [Abstract]
Cost	10,771	10,473	10,015
Gross Unrealized Gains	94	21	6
Gross Unrealized Losses	35	162	236
Fair Value	10,830	10,332	9,785
U.S. Treasury securities
Available-for-sale securities [Abstract]
Cost	180	179	242
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	2
Fair Value	$ 180	$ 179	$ 240

Fair value measurements (Detail

Fair value measurements (Details 3) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Concentration risks, percentage [Abstract]
Percentage in fixed-income and other investments	51.00%	53.00%	48.00%
Percentage investment in common stock of large-cap companies	22.00%	21.00%	23.00%
Percentage investment in common stock of mid-cap companies	12.00%	11.00%	13.00%
Percentage investment in common stock of small-cap companies	10.00%	10.00%	11.00%
Percentage investment in target date investments	4.00%	3.00%	3.00%
Percentage investment in cash and cash equivalents	1.00%	2.00%	2.00%
Fair value, measurements, recurring
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 104,960	$ 95,148	$ 98,241
Fair value, measurements, recurring | Money market funds
Fair value measurements [Line Items]
Assets, fair value disclosure	10,816	10,799	9,904
Fair value, measurements, recurring | Insurance contract
Fair value measurements [Line Items]
Assets, fair value disclosure	83,134	73,838	78,312
Fair value, measurements, recurring | Mortgage-backed securities
Fair value measurements [Line Items]
Assets, fair value disclosure	10,830	10,332	9,785
Fair value, measurements, recurring | U.S. Treasury securities
Fair value measurements [Line Items]
Assets, fair value disclosure	180	179	240
Fair value, measurements, recurring | Fair value, inputs, level 2
Fair value measurements [Line Items]
Assets, fair value disclosure	104,960	95,148	98,241
Fair value, measurements, recurring | Fair value, inputs, level 2 | Money market funds
Fair value measurements [Line Items]
Assets, fair value disclosure	10,816	10,799	9,904
Fair value, measurements, recurring | Fair value, inputs, level 2 | Insurance contract
Fair value measurements [Line Items]
Assets, fair value disclosure	83,134	73,838	78,312
Fair value, measurements, recurring | Fair value, inputs, level 2 | Mortgage-backed securities
Fair value measurements [Line Items]
Assets, fair value disclosure	10,830	10,332	9,785
Fair value, measurements, recurring | Fair value, inputs, level 2 | U.S. Treasury securities
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 180	$ 179	$ 240

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	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Fair value, balance sheet grouping [Line Items]
Long-term debt	$ 2,379,806	$ 2,108,695
Carrying Amount
Fair value, balance sheet grouping [Line Items]
Long-term debt	2,379,806	2,108,695	$ 1,852,910
Fair Value
Fair value, balance sheet grouping [Line Items]
Long-term debt, fair value	$ 2,521,325	$ 2,183,819	$ 1,949,564

Short-term debt (Details)

Short-term debt (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Apr. 12, 2019	Mar. 22, 2019	Dec. 31, 2018	Jun. 30, 2018
Short-term Debt [Line Items]
Short-term borrowings	$ 89,983			$ 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

Long-term debt Issued (Details

Long-term debt Issued (Details 2) - USD ($) $ in Thousands	Jun. 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	$ 2,379,806				$ 2,108,695
Senior Notes
Long-term debt issued [Line Items]
Long-term debt	$ 1,656,000				1,381,000
Weighted Average Interest Rate	4.52%
Credit Agreements
Long-term debt issued [Line Items]
Long-term debt	$ 11,075				$ 110,100
Weighted Average Interest Rate	5.50%
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	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Long-term debt outstanding [Line Items]
Long-term debt	$ 2,379,806	$ 2,108,695
Long-term debt due within one year	51,822	251,854	$ 109,199
Long-term debt	$ 2,327,984	1,856,841	$ 1,743,711
Senior Notes
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	4.52%
Long-term debt	$ 1,656,000	1,381,000
Commercial Paper
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	2.77%
Long-term debt	$ 433,350	338,100
Term Loan Agreements
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	2.75%
Long-term debt	$ 209,800	209,800
Credit Agreements
Long-term debt outstanding [Line Items]
Weighted Average Interest Rate	5.50%
Long-term debt	$ 11,075	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	$ 26,105	25,229
Long-term Debt
Long-term debt outstanding [Line Items]
Unamortized Debt Issuance Costs	6,164	5,207
Discount	$ 360	$ 327

Schedule of debt maturities (De

Schedule of debt maturities (Details 4) $ in Thousands	Jun. 30, 2019USD ($)
Long-term debt maturities [Line Items]
Remainder of 2019	$ 51,761
2020	15,926
2021	386,430
2022	147,434
2023	125,188
Thereafter	$ 1,659,591

Cash flow information (Details)

Cash flow information (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Interest, net	$ 45,702	$ 39,467
Income taxes paid, net	4,124	4,034
AFUDC borrowed	1,200	1,000
Right-of-use assets obtained in exchange for new operating lease liabilities	24,990	0	$ 0
Property, plant and equipment additions in accounts payable	27,312	30,985	42,355
Debt assumed in connection with a business combination	1,163	0	0
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	$ 3,100

Business segment data (Details)

Business segment data (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 1,303,573		$ 1,064,597		$ 2,394,764	$ 2,040,890
Operating Income (Loss)	97,311		73,992		161,530	143,368
Income from continuing operations	63,145		44,075		104,234	86,036
Income (loss) from discontinued operations, net of tax	(1,320)		(273)		(1,483)	203
Net income	61,825	$ 40,926	43,802	$ 42,437	102,751	86,239
Electric
Segment Reporting Information [Line Items]
Revenues	81,011		78,499		173,578	165,904
Operating Income (Loss)	9,791		13,027		27,779	31,182
Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	133,867		129,540		476,014	462,204
Operating Income (Loss)	(2,621)		(4,371)		47,696	44,169
Pipeline and midstream
Segment Reporting Information [Line Items]
Revenues	28,680		24,060		37,293	32,893
Operating Income (Loss)	10,698		8,482		20,602	16,650
Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	595,799		509,388		822,911	722,672
Operating Income (Loss)	46,178		37,301		4,597	10,992
Construction services
Segment Reporting Information [Line Items]
Revenues	464,192		323,020		884,925	657,071
Operating Income (Loss)	31,966		19,356		59,431	39,990
Other
Segment Reporting Information [Line Items]
Revenues	24		90		43	146
Operating Income (Loss)	1,299		197		1,425	385
Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(11,281)		(9,981)		(43,285)	(34,490)
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	(7,513)		(6,539)		(31,468)	(28,298)
Intersegment eliminations | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	(168)		(235)		(264)	(336)
Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	(721)		(540)		(849)	(550)
Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	(2,879)		(2,667)		(10,704)	(5,306)
Total intersegment operating revenues
Segment Reporting Information [Line Items]
Revenues	0		0		0	0
Regulated operation
Segment Reporting Information [Line Items]
Revenues	236,247		226,684		675,864	651,143
Income from continuing operations	7,597		7,521		66,606	58,686
Regulated operation | Electric
Segment Reporting Information [Line Items]
Revenues	81,011		78,499		173,578	165,904
Income from continuing operations	7,471		9,133		22,976	22,216
Regulated operation | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	133,867		129,540		476,014	462,204
Income from continuing operations	(6,252)		(6,852)		30,248	25,771
Regulated operation | Pipeline and midstream
Segment Reporting Information [Line Items]
Revenues	21,369		18,645		26,272	23,035
Income from continuing operations	6,378		5,240		13,382	10,699
Regulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	7,426		6,446		31,349	28,182
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	7,426		6,446		31,349	28,182
Nonregulated operation
Segment Reporting Information [Line Items]
Revenues	1,067,326		837,913		1,718,900	1,389,747
Income from continuing operations	55,548		36,554		37,628	27,350
Nonregulated operation | Pipeline and midstream
Segment Reporting Information [Line Items]
Revenues	7,311		5,415		11,021	9,858
Income from continuing operations	742		467		579	288
Nonregulated operation | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	595,799		509,388		822,911	722,672
Income from continuing operations	29,166		24,336		(5,283)	815
Nonregulated operation | Construction services
Segment Reporting Information [Line Items]
Revenues	464,192		323,020		884,925	657,071
Income from continuing operations	22,845		14,088		42,869	29,179
Nonregulated operation | Other
Segment Reporting Information [Line Items]
Revenues	24		90		43	146
Income from continuing operations	2,795		(2,337)		(537)	(2,932)
Nonregulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	3,855		3,535		11,936	6,308
Nonregulated operation | Intersegment eliminations | Pipeline and midstream
Segment Reporting Information [Line Items]
Revenues	87		93		119	116
Nonregulated operation | Intersegment eliminations | Construction materials and contracting
Segment Reporting Information [Line Items]
Revenues	168		235		264	336
Nonregulated operation | Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	721		540		849	550
Nonregulated operation | Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	$ 2,879		$ 2,667		$ 10,704	$ 5,306

Employee benefit plans (Details

Employee benefit plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	3,840	3,488	7,613	7,295
Expected return on assets	(3,998)	(5,379)	(9,118)	(10,377)
Amortization of prior service credit	0	0	0	0
Amortization of net actuarial (gain) loss	1,418	1,721	2,773	3,503
Net periodic benefit cost (credit), including amount capitalized	1,260	(170)	1,268	421
Less amount capitalized	0	0	0	0
Net periodic benefit cost (credit)	1,260	(170)	1,268	421
Qualified plan | Overfunded Plan [Member] | Other postretirement benefits
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	227	340	571	747
Interest cost	713	672	1,493	1,450
Expected return on assets	(1,182)	(1,266)	(2,402)	(2,433)
Amortization of prior service credit	(228)	(348)	(577)	(697)
Amortization of net actuarial (gain) loss	(42)	82	55	320
Net periodic benefit cost (credit), including amount capitalized	(512)	(520)	(860)	(613)
Less amount capitalized	27	43	58	83
Net periodic benefit cost (credit)	(539)	(563)	(918)	(696)
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	$ 2,200	$ 2,200

MNPUC (Details)

MNPUC (Details) - Tax Cuts and Jobs Act [Member] - Natural gas rate proceeding [Member] - MNPUC [Member]	Apr. 18, 2019USD ($)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ (400,000)
Public Utilities, Approved One-Time Increase (Decrease) to Customers, Amount	$ (600,000)

MTPSC (Details 2)

MTPSC (Details 2) - MTPSC - USD ($)	Apr. 24, 2019	Mar. 07, 2019	Sep. 28, 2018
Electric rate proceeding
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 9,000,000		$ 11,900,000
Public utilities, requested rate increase (decrease), percentage			18.90%
Public utilities, interim rate increase (decrease), amount		$ 7,900,000
Public utilities, interim rate increase (decrease), percentage		12.80%
Future Electric Rate Proceeding [Member]
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 300,000

NDPSC (Details 3)

NDPSC (Details 3) - NDPSC - USD ($)	Jul. 19, 2019	Jan. 23, 2019
Subsequent Event [Member] | Electric rate proceeding
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 1,500,000
Tax Cuts and Jobs Act [Member] | Natural gas rate proceeding [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ (168,000)
Public Utilities, Approved One-Time Increase (Decrease) to Customers, Amount		$ (200,000)

OPUC (Details 4)

OPUC (Details 4) - Tax Cuts and Jobs Act [Member] - Natural gas rate proceeding [Member] - OPUC - USD ($)	Mar. 14, 2019	May 31, 2018
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount		$ 2,300,000
Public utilities, requested rate increase (decrease), percentage		3.50%
Public Utilities, Approved Rate Increase (Decrease) in Revenues Only, Amount	$ 1,700,000
Public Utilities, Approved Rate Increase (Decrease) in Taxes Only, Amount	(500,000)
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 1,200,000

WUTC (Details 5)

WUTC (Details 5) - Natural gas rate proceeding [Member] - WUTC - USD ($) $ in Millions	May 31, 2019	Mar. 29, 2019	Mar. 28, 2019
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount			$ 48
Public utilities, requested rate increase (decrease), amount	$ 1.6	$ 12.7
Public utilities, requested rate increase (decrease), percentage	0.70%	5.50%

WYPSC (Details 6)

WYPSC (Details 6) - WYPSC - USD ($)	Jul. 16, 2019	May 23, 2019	Apr. 08, 2019
Natural gas rate proceeding [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%
Tax Cuts and Jobs Act [Member] | Electric rate proceeding
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%)
Public Utilities, Approved One-Time Increase (Decrease) to Customers, Amount			$ (1,600,000)
Subsequent Event [Member] | Tax Cuts and Jobs Act [Member] | Natural gas rate proceeding [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Proposed One-Time Increase (Decrease) to Customers, Amount	$ (190,000)

FERC (Details 7)

FERC (Details 7) $ in Millions	May 30, 2019USD ($)
Tax Cuts and Jobs Act [Member] | Natural gas rate proceeding [Member] | FERC [Member]
Public Utilities, General Disclosures [Line Items]
Public utilities, interim rate increase (decrease), amount	$ 4.5

Litigation (Details)

Litigation (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Loss Contingencies [Line Items]
Potential liabilities related to litigation and environmental matters	$ 32.1	$ 30.4	$ 31.1

Environmental matters (Details

Environmental matters (Details 2) - USD ($)	6 Months Ended
	Jun. 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
Eugene, OR manufactured gas plant site
Site Contingency [Line Items]
Total estimated costs for site remediation	2,400,000
Incurred costs for site remediation	$ 400,000
Estimated proportional share of cleanup liability	50.00%
Environmental matters accrual for site remediation	$ 1,000,000
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	3,600,000
Environmental matters accrual of investigative costs	4,000,000
Bellingham, WA manufactured gas plant site
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, preferred alternative estimate	9,300,000
Missoula, MT manufactured gas plant site
Site Contingency [Line Items]
Total estimated costs for site remediation	560,000
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)	Jun. 30, 2019USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 274,200,000
Fixed maximum amounts guaranteed by year 2019	85,500,000
Fixed maximum amounts guaranteed by year 2020	181,400,000
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	4,000,000
Amount outstanding under guarantees that is reflected on balance sheet	0
Letters of credit	32,800,000
Letters of credit set to expire - 2019	29,400,000
Letters of credit set to expire - 2020	3,400,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	$ 1,100,000,000

Variable interest entities (Det

Variable interest entities (Details 4) $ in Millions	Jun. 30, 2019USD ($)
Fuel contract
Variable Interest Entities [Line Items]
Variable interest entity, reporting entity involvement, maximum loss exposure, amount	$ 37.3