MDU Resources (MDU) 10-Q 4 Aug 17 2017 Q2 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2017	Jul. 28, 2017
Entity Information [Line Items]
Entity registrant name	MDU RESOURCES GROUP INC
Entity central index key	67,716
Current fiscal year end date	--12-31
Entity filer category	Large Accelerated Filer
Document type	10-Q
Document period end date	Jun. 30, 2017
Document fiscal year focus	2,017
Document fiscal period focus	Q2
Amendment flag	false
Entity common stock, shares outstanding		195,304,376

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating revenues:
Electric, natural gas distribution and regulated pipeline and midstream		$ 225,485	$ 206,052	$ 659,100	$ 591,918
Nonregulated pipeline and midstream, construction materials and contracting, construction services and other		842,154	837,896	1,346,465	1,312,245
Total operating revenues		1,067,639	1,043,948	2,005,565	1,904,163
Operating expenses:
Electric fuel and purchased power		16,752	15,914	38,638	37,925
Purchased natural gas sold		57,668	47,439	250,617	208,474
Operation and maintenance:
Electric, natural gas distribution and regulated pipeline and midstream		77,273	77,078	156,013	151,703
Nonregulated pipeline and midstream, construction materials and contracting, construction services and other		743,656	722,742	1,222,132	1,165,243
Depreciation, depletion and amortization		51,658	54,248	102,983	109,132
Taxes, other than income		40,953	37,562	88,391	80,736
Total operating expenses		987,960	954,983	1,858,774	1,753,213
Operating income		79,679	88,965	146,791	150,950
Other income		782	872	1,798	1,921
Interest expense		20,766	22,219	41,068	45,087
Income before income taxes		59,695	67,618	107,521	107,784
Income taxes		15,290	21,320	27,478	29,620
Income from continuing operations		44,405	46,298	80,043	78,164
Loss from discontinued operations, net of tax (Note 8)	[1]	(3,190)	(276,102)	(1,504)	(294,138)
Net income (loss)		41,215	(229,804)	78,539	(215,974)
Loss from discontinued operations attributable to noncontrolling interest (Note 8)		0	(120,651)	0	(131,691)
Loss on redemption of preferred stocks		600	0	600	0
Dividends declared on preferred stocks		0	171	171	343
Earnings (loss) on common stock		$ 40,615	$ (109,324)	$ 77,768	$ (84,626)
Earnings (loss) per common share - basic:
Earnings before discontinued operations		$ 0.22	$ 0.24	$ 0.41	$ 0.40
Discontinued operations attributable to the Company, net of tax		(0.01)	(0.80)	(0.01)	(0.83)
Earnings (loss) per common share - basic		0.21	(0.56)	0.40	(0.43)
Earnings (loss) per common share - diluted:
Earnings before discontinued operations		0.22	0.24	0.40	0.40
Discontinued operations attributable to the Company, net of tax		(0.01)	(0.80)	0	(0.83)
Earnings (loss) per common share - diluted		0.21	(0.56)	0.40	(0.43)
Dividends declared per common share		$ 0.1925	$ 0.1875	$ 0.3850	$ 0.3750
Weighted average common shares outstanding - basic		195,304	195,304	195,304	195,294
Weighted average common shares outstanding - diluted		195,973	195,699	195,993	195,678
[1]	Includes eliminations for the presentation of income tax adjustments between continuing and discontinued operations.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net income (loss)	$ 41,215	$ (229,804)	$ 78,539	$ (215,974)
Net unrealized gain on derivative instruments qualifying as hedges:
Reclassification adjustment for loss on derivative instruments included in net income (loss), net of tax of $56 and $56 for the three months ended and $112 and $114 for the six months ended in 2017 and 2016, respectively	92	91	183	183
Postretirement liability adjustment:
Amortization of postretirement liability (gains) losses included in net periodic benefit cost (credit), net of tax of $190 and $150 for the three months ended and $406 and $(819) for the six months ended in 2017 and 2016, respectively	312	248	669	(1,347)
Reclassification of postretirement liability adjustment from regulatory asset, net of tax of $0 and $0 for the three months ended and $(725) and $0 in 2017 and 2016, respectively	0	0	(917)	0
Postretirement liability adjustment	312	248	(248)	(1,347)
Foreign currency translation adjustment:
Foreign currency translation adjustment recognized during the period, net of tax of $(9) and $19 for the three months ended and $(3) and $33 for the six months ended in 2017 and 2016, respectively	(15)	31	(6)	56
Net unrealized gain on available-for-sale investments:
Net unrealized loss on available-for-sale investments arising during the period, net of tax of $(13) and $(16) for the three months ended and $(28) and $(10) for the six months ended in 2017 and 2016, respectively	(24)	(30)	(51)	(19)
Reclassification adjustment for loss on available-for-sale investments included in net income (loss), net of tax of $17 and $19 for the three months ended and $36 and $37 for the six months ended in 2017 and 2016, respectively	31	36	66	69
Net unrealized gain on available-for-sale investments	7	6	15	50
Other comprehensive income (loss)	396	376	(56)	(1,058)
Comprehensive income (loss)	41,611	(229,428)	78,483	(217,032)
Loss from discontinued operations attributable to noncontrolling interest	0	(120,651)	0	(131,691)
Comprehensive income (loss) attributable to common stockholders	$ 41,611	$ (108,777)	$ 78,483	$ (85,341)

Consolidated Statements of Com4

Consolidated Statements of Comprehensive Income - Parenthetical - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification adjustment for (gain) loss on derivative instruments included in net income (loss), tax	$ 56	$ 56	$ 112	$ 114
Amortization of postretirement liability (gains) losses included in net periodic benefit cost, tax	190	150	406	(819)
Reclassification of postretirement liability adjustment from regulatory asset, tax	0	0	(725)	0
Foreign currency translation adjustments recognized during the period, tax	(9)	19	(3)	33
Net unrealized gain (loss) on available-for-sale investments arising during the period, tax	(13)	(16)	(28)	(10)
Reclassification adjustment for loss (gain) on available-for-sale investments included in net income (loss), tax	$ 17	$ 19	$ 36	$ 37

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Current assets:
Cash and cash equivalents	$ 40,048	$ 46,107	$ 85,117
Receivables, net	661,771	630,243	637,166
Inventories	249,870	238,273	265,849
Prepayments and other current assets	63,953	48,461	50,309
Current assets held for sale	328	14,391	37,625
Total current assets	1,015,970	977,475	1,076,066
Investments	131,726	125,866	124,531
Property, plant and equipment	6,591,382	6,510,229	6,526,563
Less accumulated depreciation, depletion and amortization	2,638,098	2,578,902	2,551,941
Net property, plant and equipment	3,953,284	3,931,327	3,974,622
Deferred charges and other assets:
Goodwill	631,791	631,791	641,527	[1]
Other intangible assets, net	4,785	5,925	7,160
Other	416,759	415,419	360,520
Noncurrent assets held for sale	76,183	196,664	167,100
Total deferred charges and other assets	1,129,518	1,249,799	1,176,307
Total assets	6,230,498	6,284,467	6,351,526
Current liabilities:
Long-term debt due within one year	83,499	43,598	58,598
Accounts payable	279,211	279,962	275,791
Taxes payable	55,037	48,164	45,749
Dividends payable	37,596	37,767	36,791
Accrued compensation	52,951	65,867	56,390
Other accrued liabilities	181,030	184,377	196,701
Current liabilities held for sale	4,481	9,924	28,237
Total current liabilities	693,805	669,659	698,257
Long-term debt	1,677,977	1,746,561	1,928,709
Deferred credits and other liabilities:
Deferred income taxes	668,239	668,226	666,601
Other	887,525	883,777	820,349
Total deferred credits and other liabilities	1,555,764	1,552,003	1,486,950
Commitments and contingencies
Stockholders' equity:
Preferred stocks	0	15,000	15,000
Common stockholders' equity:
Authorized - 500,000,000 shares, $1.00 par value Shares issued - 195,843,297 at June 30, 2017 and 2016 and December 31, 2016	195,843	195,843	195,843
Other paid-in capital	1,231,892	1,232,478	1,230,342
Retained earnings	914,632	912,282	838,257
Accumulated other comprehensive loss	(35,789)	(35,733)	(38,206)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)	(3,626)
Total common stockholders' equity	2,302,952	2,301,244	2,222,610
Total stockholders' equity	2,302,952	2,316,244	2,237,610
Total liabilities and stockholders' equity	$ 6,230,498	$ 6,284,467	$ 6,351,526
[1]	Balance is presented net of accumulated impairment of $12.3 million at the pipeline and midstream segment, which occurred in prior periods.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Stockholders' equity:
Common stock, shares authorized	500,000,000	500,000,000	500,000,000
Common stock, par value	$ 1	$ 1	$ 1
Common stock, shares issued	195,843,297	195,843,297	195,843,297
Treasury shares	538,921	538,921	538,921

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016
Operating activities:
Net income (loss)		$ 78,539	$ (215,974)
Loss from discontinued operations, net of tax	[1]	(1,504)	(294,138)
Income from continuing operations		80,043	78,164
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization		102,983	109,132
Deferred income taxes		(5,293)	3,608
Changes in current assets and liabilities, net of acquisitions:
Receivables		(43,478)	(44,909)
Inventories		(13,573)	(23,189)
Other current assets		(15,799)	(20,555)
Accounts payable		11,611	7,339
Other current liabilities		(6,387)	33,214
Other noncurrent changes		(4,460)	(14,626)
Net cash provided by continuing operations		105,647	128,178
Net cash provided by (used in) discontinued operations		33,846	(25,529)
Net cash provided by operating activities		139,493	102,649
Investing activities:
Capital expenditures		(143,764)	(220,098)
Net proceeds from sale or disposition of property and other		119,361	14,778
Investments		(358)	(262)
Net cash used in continuing operations		(24,761)	(205,582)
Net cash provided by discontinued operations		2,234	28,040
Net cash used in investing activities		(22,527)	(177,542)
Financing activities:
Issuance of long-term debt		63,827	387,625
Repayment of long-term debt		(93,275)	(196,771)
Dividends paid		(75,535)	(73,575)
Redemption of preferred stock		(15,600)	0
Repurchase of common stock		(1,684)	0
Tax withholding on stock-based compensation		(757)	(323)
Net cash provided by (used in) continuing operations		(123,024)	116,956
Net cash used in discontinued operations		0	(40,852)
Net cash provided by (used in) financing activities		(123,024)	76,104
Effect of exchange rate changes on cash and cash equivalents		(1)	3
Increase (decrease) in cash and cash equivalents		(6,059)	1,214
Cash and cash equivalents -- beginning of year		46,107	83,903
Cash and cash equivalents -- end of period		$ 40,048	$ 85,117
[1]	Includes eliminations for the presentation of income tax adjustments between continuing and discontinued operations.

Basis of presentation

Basis of presentation	6 Months Ended
	Jun. 30, 2017
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 2016 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. Management has also evaluated the impact of events occurring after June 30, 2017 , up to the date of issuance of these consolidated interim financial statements. 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 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. The Company's consolidated financial statements and accompanying notes for current and prior periods have been restated. 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 8 .

Seasonality of operations

Seasonality of operations	6 Months Ended
	Jun. 30, 2017
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, 2017
Receivables [Abstract]
Accounts receivable and allowance for doubtful accounts	Accounts receivable and allowance for doubtful accounts Accounts receivable consist 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 $32.7 million , $31.7 million and $29.2 million at June 30, 2017 and 2016 , and December 31, 2016 , 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, 2017 and 2016 , and December 31, 2016 , was $9.2 million , $11.0 million and $10.5 million , respectively.

Inventories and natural gas in

Inventories and natural gas in storage	6 Months Ended
	Jun. 30, 2017
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 is included in inventories. Inventories consisted of: June 30, 2017 June 30, 2016 December 31, 2016 (In thousands) Aggregates held for resale $ 123,316 $ 130,544 $ 115,471 Asphalt oil 46,852 42,591 29,103 Materials and supplies 22,657 20,765 18,372 Merchandise for resale 16,164 18,439 16,437 Natural gas in storage (current) 14,126 19,689 25,761 Other 26,755 33,821 33,129 Total $ 249,870 $ 265,849 $ 238,273 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 $ 49.5 million , $ 49.1 million and $ 49.5 million at June 30, 2017 and 2016 , and December 31, 2016 , respectively.

Earnings (loss) per common shar

Earnings (loss) per common share	6 Months Ended
	Jun. 30, 2017
Earnings Per Share [Abstract]
Earnings (loss) per common share	Earnings (loss) per common share Basic earnings (loss) per common share were computed by dividing earnings (loss) on common stock by the weighted average number of shares of common stock outstanding during the applicable period. Diluted earnings (loss) per common share were computed by dividing earnings (loss) on common stock by the total of the weighted average number of shares of common stock outstanding during the applicable period, plus the effect of outstanding performance share awards. Common stock outstanding includes issued shares less shares held in treasury. Net income (loss) was the same for both the basic and diluted earnings (loss)per share calculations. A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings (loss) per share calculations was as follows: Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 (In thousands) Weighted average common shares outstanding - basic 195,304 195,304 195,304 195,294 Effect of dilutive performance share awards 669 395 689 384 Weighted average common shares outstanding - diluted 195,973 195,699 195,993 195,678 Shares excluded from the calculation of diluted earnings per share — — — —

New accounting standards

New accounting standards	6 Months Ended
	Jun. 30, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New accounting standards	New accounting standards Recently adopted accounting standards Balance Sheet Classification of Deferred Taxes In November 2015, the FASB issued guidance regarding the classification of deferred taxes on the balance sheet. The guidance requires all deferred tax assets and liabilities to be classified as noncurrent. These amendments align GAAP with IFRS. The Company adopted the guidance in the fourth quarter of 2016 and applied the retrospective method of adoption. The guidance required a reclassification of current deferred income taxes to noncurrent deferred income taxes on the Consolidated Balance Sheets, but did not impact the Company's results of operations or cash flows. As a result of the retrospective application of this change in accounting principle, the Company reclassified deferred income taxes of $33.9 million from current assets - deferred income taxes to deferred credits and other liabilities - deferred income taxes on its Consolidated Balance Sheet at June 30, 2016. Simplifying the Measurement of Inventory In July 2015, the FASB issued guidance regarding inventory that is measured using the first-in, first-out or average cost method. The guidance does not apply to inventory measured using the last-in, first-out or the retail inventory method. The guidance requires inventory within its scope to be measured at the lower of cost or net realizable value, which is the estimated selling price in the normal course of business less reasonably predictable costs of completion, disposal and transportation. These amendments more closely align GAAP with IFRS. The Company adopted the guidance on January 1, 2017, on a prospective basis. The guidance did not have a material effect on the Company's results of operations, financial position, cash flows or disclosures. Improvements to Employee Share-Based Payment Accounting In March 2016, the FASB issued guidance regarding simplification of several aspects of the accounting for share-based payment transactions. The guidance affects the income tax consequences, classification of awards as either equity or liabilities, classification on the statement of cash flows and calculation of dilutive shares. The Company adopted the guidance on January 1, 2017. All amendments in the guidance that apply to the Company were adopted on a prospective basis resulting in no adjustments being made to retained earnings. The adoption of the guidance impacted the Consolidated Statement of Income and the Consolidated Balance Sheet in the first quarter of 2017 due to the taxes related to the stock-based compensation award that vested in February 2017 being recognized as income tax expense as compared to a reduction to additional paid-in capital under the previous guidance. Adoption of the guidance also increased the number of shares included in the diluted earnings per share calculation due to the exclusion of tax benefits in the incremental shares calculation. The change in the weighted average common shares outstanding - diluted did not result in a material effect on the earnings per common share - diluted. Recently issued accounting standards not yet adopted Revenue from Contracts with Customers In May 2014, the FASB issued guidance on accounting for revenue from contracts with customers. The guidance provides for a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry specific guidance. In August 2015, the FASB issued guidance deferring the effective date of the revenue guidance and allowing entities to early adopt. With this decision, the guidance will be effective for the Company on January 1, 2018. Entities will have the option of using either a full retrospective or modified retrospective approach to adopting the guidance. The Company plans to adopt the guidance on January 1, 2018, and to use the modified retrospective approach. Under the modified approach, an entity would recognize the cumulative effect of initially applying the guidance with an adjustment to the opening balance of retained earnings in the period of adoption. In addition, the guidance will require expanded disclosures, both quantitative and qualitative, related to the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. The Company does not anticipate a significant change in the timing of revenue recognition and continues to evaluate all revenue streams to determine what effect the guidance will have on its results of operations, financial position, cash flows and disclosures. Recognition and Measurement of Financial Assets and Financial Liabilities In January 2016, the FASB issued guidance regarding the classification and measurement of financial instruments. The guidance revises the way an entity classifies and measures investments in equity securities, the presentation of certain fair value changes for financial liabilities measured at fair value and amends certain disclosure requirements related to the fair value of financial instruments. This guidance will be effective for the Company on January 1, 2018, with early adoption of certain amendments permitted. The guidance should be applied using a modified retrospective approach with the exception of equity securities without readily determinable fair values which will be applied prospectively. The Company is evaluating the effects the adoption of the new guidance will have on its results of operations, financial position, cash flows and disclosures. Classification of Certain Cash Receipts and Cash Payments In August 2016, the FASB issued guidance to clarify the classification of certain cash receipts and payments in the statement of cash flows. The guidance is intended to standardize the presentation and classification of certain transactions, including cash payments for debt prepayment or extinguishment, proceeds from insurance claim settlements and distributions from equity method investments. In addition, the guidance clarifies how to classify transactions that have characteristics of more than one class of cash flows. This guidance will be effective for the Company on January 1, 2018, with early adoption permitted. An entity that elects early adoption must adopt all the amendments in the same period and apply any adjustments as of the beginning of the fiscal year. Entities must apply the guidance retrospectively unless it is impracticable to do so, in which case they may apply it prospectively as of the earliest date practicable. The Company is evaluating the effects the adoption of the new guidance will have on its cash flows and disclosures. Clarifying the Definition of a Business In January 2017, the FASB issued guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions or disposals of assets or businesses. The guidance provides a screen to determine when an integrated set of assets and activities is not a business. The guidance will also affect other aspects of accounting, such as determining reporting units for goodwill testing and whether an entity has acquired or sold a business. The guidance will be effective for the Company on January 1, 2018, and should be applied on a prospective basis with early adoption permitted for transactions that occur before the issuance or effective date of the amendments and only when the transactions have not been reported in the financial statements or made available for issuance. The Company expects to adopt this guidance as required and does not expect the guidance to have a material effect on its results of operations, financial position, cash flows and disclosures. Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost In March 2017, the FASB issued guidance to improve the presentation of net periodic pension cost and net periodic postretirement benefit cost. The guidance requires the service cost component to be presented in the income statement in the same line item or items as other compensation costs arising from services performed during the period. Other components of net benefit cost shall be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. The guidance also only allows the service cost component to be capitalized. The guidance will be effective for the Company on January 1, 2018, including interim periods, with early adoption permitted as of the beginning of an annual period for which the financial statements have not been issued. The guidance shall be applied on a retrospective basis for the financial statement presentation and on a prospective basis for the capitalization of the service cost component. The Company is evaluating the effects the adoption of the new guidance will have on its results of operations, financial position, cash flows and disclosures. Leases In February 2016, the FASB issued guidance regarding leases. The guidance requires lessees to recognize a lease liability and a right-of-use asset on the balance sheet for operating and financing leases with terms of more than 12 months. The guidance remains 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 requires additional disclosures, both quantitative and qualitative, related to operating and finance leases for the lessee and sales-type, direct financing and operating leases for the lessor. This guidance will be effective for the Company on January 1, 2019, and should be applied using a modified retrospective approach with early adoption permitted. There continues to be industry-specific implementation issues that are unresolved and the final resolution of these issues could significantly impact the number of contracts that would be considered a lease for the Company under the new guidance. Due to the uncertainty of these issues, the Company cannot estimate the potential impact the adoption of the new guidance will have on its results of operations, financial position, cash flows and disclosures. The Company is planning to adopt the standard on January 1, 2019, utilizing the practical expedient that allows the Company to not reassess whether an expired or existing contract contains a lease, the classification of leases or initial direct costs. 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 should be applied on a prospective basis with early adoption permitted. The Company is evaluating the effects the adoption of the new guidance will have on its results of operations, financial position, cash flows and disclosures.

Comprehensive income (loss)

Comprehensive income (loss)	6 Months Ended
	Jun. 30, 2017
Equity [Abstract]
Comprehensive income (loss)	Comprehensive income (loss) The after-tax changes in the components of accumulated other comprehensive loss were as follows: Three Months Ended June 30, 2017 Net Unrealized Gain (Loss) on Derivative Instruments Qualifying as Hedges Postretirement Liability Adjustment Foreign Currency Translation Adjustment Net Unrealized Gain (Loss) on Available-for-sale Investments Total Accumulated Other Comprehensive Loss (In thousands) Balance at beginning of period $ (2,209 ) $ (33,781 ) $ (140 ) $ (55 ) $ (36,185 ) Other comprehensive loss before reclassifications — — (15 ) (24 ) (39 ) Amounts reclassified from accumulated other comprehensive loss 92 312 — 31 435 Net current-period other comprehensive income (loss) 92 312 (15 ) 7 396 Balance at end of period $ (2,117 ) $ (33,469 ) $ (155 ) $ (48 ) $ (35,789 ) Three Months Ended June 30, 2016 Net Unrealized Gain (Loss) on Derivative Instruments Qualifying as Hedges Postretirement Liability Adjustment Foreign Currency Translation Adjustment Net Unrealized Gain (Loss) on Available-for-sale Investments Total Accumulated Other Comprehensive Loss (In thousands) Balance at beginning of period $ (2,575 ) $ (35,852 ) $ (175 ) $ 20 $ (38,582 ) Other comprehensive income (loss) before reclassifications — — 31 (30 ) 1 Amounts reclassified from accumulated other comprehensive loss 91 248 — 36 375 Net current-period other comprehensive income 91 248 31 6 376 Balance at end of period $ (2,484 ) $ (35,604 ) $ (144 ) $ 26 $ (38,206 ) Six Months Ended June 30, 2017 Net Unrealized Gain (Loss) on Derivative Instruments Qualifying as Hedges Postretirement Liability Adjustment Foreign Currency Translation Adjustment Net Unrealized Gain (Loss) on Available-for-sale Investments Total Accumulated Other Comprehensive Loss (In thousands) Balance at beginning of period $ (2,300 ) $ (33,221 ) $ (149 ) $ (63 ) $ (35,733 ) Other comprehensive loss before reclassifications — — (6 ) (51 ) (57 ) Amounts reclassified from accumulated other comprehensive loss 183 669 — 66 918 Amounts reclassified to accumulated other comprehensive loss from a regulatory asset — (917 ) — — (917 ) Net current-period other comprehensive income (loss) 183 (248 ) (6 ) 15 (56 ) Balance at end of period $ (2,117 ) $ (33,469 ) $ (155 ) $ (48 ) $ (35,789 ) Six Months Ended June 30, 2016 Net Unrealized Gain (Loss) on Derivative Instruments Qualifying as Hedges Postretirement Liability Adjustment Foreign Currency Translation Adjustment Net Unrealized Gain (Loss) on Available-for-sale Investments Total Accumulated Other Comprehensive Loss (In thousands) Balance at beginning of period $ (2,667 ) $ (34,257 ) $ (200 ) $ (24 ) $ (37,148 ) Other comprehensive income (loss) before reclassifications — — 56 (19 ) 37 Amounts reclassified from accumulated other comprehensive loss 183 (1,347 ) — 69 (1,095 ) Net current-period other comprehensive income (loss) 183 (1,347 ) 56 50 (1,058 ) Balance at end of period $ (2,484 ) $ (35,604 ) $ (144 ) $ 26 $ (38,206 ) Reclassifications out of accumulated other comprehensive loss were as follows: Three Months Ended Six Months Ended Location on Consolidated Statements of Income June 30, June 30, 2017 2016 2017 2016 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income (loss) $ (148 ) $ (147 ) $ (295 ) $ (297 ) Interest expense 56 56 112 114 Income taxes (92 ) (91 ) (183 ) (183 ) Amortization of postretirement liability gains (losses) included in net periodic benefit cost (credit) (502 ) (398 ) (1,075 ) 2,166 (a) 190 150 406 (819 ) Income taxes (312 ) (248 ) (669 ) 1,347 Reclassification adjustment for loss on available-for-sale investments included in net income (loss) (48 ) (55 ) (102 ) (106 ) Other income 17 19 36 37 Income taxes (31 ) (36 ) (66 ) (69 ) Total reclassifications $ (435 ) $ (375 ) $ (918 ) $ 1,095 (a) Included in net periodic benefit cost (credit). For more information, see Note 14 .

Assets held for sale and discon

Assets held for sale and discontinued operations	6 Months Ended
	Jun. 30, 2017
Discontinued Operations and Disposal Groups [Abstract]
Assets held for sale and discontinued operations	Assets held for sale and discontinued operations Assets held for sale The assets and liabilities of Pronghorn were classified as held for sale in the fourth quarter of 2016. Pronghorn's results of operations for 2016 were included in the pipeline and midstream segment. Pronghorn On November 21, 2016, WBI Energy Midstream announced it had entered into a purchase and sale agreement to sell its 50 percent non-operating ownership interest in Pronghorn to Tesoro Logistics. The transaction closed on January 1, 2017, which generated approximately $100 million of proceeds for the Company. The sale of Pronghorn further reduces the Company's risk exposure to commodity prices. The carrying amounts of the major classes of assets and liabilities that were classified as held for sale associated with Pronghorn on the Company's Consolidated Balance Sheets were as follows: December 31, 2016 (In thousands) Assets Current assets: Prepayments and other current assets $ 68 Total current assets held for sale 68 Noncurrent assets: Net property, plant and equipment 93,424 Goodwill 9,737 Less allowance for impairment of assets held for sale 2,311 Total noncurrent assets held for sale 100,850 Total assets held for sale $ 100,918 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 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. The Company's consolidated financial statements and accompanying notes for current and prior periods have been restated. 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 of 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 reduces the Company’s risk by decreasing exposure to commodity prices. In connection with the sale, WBI Energy had cash in an escrow account for RINs obligations, which was included in current assets held for sale on the Consolidated Balance Sheet at June 30, 2016 . The Company retained certain liabilities of Dakota Prairie Refining which were reflected in current liabilities held for sale on the Consolidated Balance Sheets. Centennial continues to guarantee certain debt obligations of Dakota Prairie Refining; however, Tesoro has agreed to indemnify Centennial for any losses and litigation expenses arising from the guarantee. For more information related to the guarantee, see Note 16 . The carrying amounts of the major classes of assets and liabilities that are classified as held for sale related to the operations of and activity associated with Dakota Prairie Refining on the Company's Consolidated Balance Sheets were as follows: June 30, 2017 June 30, 2016 December 31, 2016 (In thousands) Assets Current assets: Receivables, net $ — $ 433 $ — Income taxes receivable 5,552 (a) 12,550 13,987 Prepayments and other current assets — 11,083 — Total current assets held for sale 5,552 24,066 13,987 Noncurrent assets: Deferred income taxes — 57,644 — Total noncurrent assets held for sale — 57,644 — Total assets held for sale $ 5,552 $ 81,710 $ 13,987 Liabilities Current liabilities: Accounts payable $ — $ 7,170 $ 7,425 Other accrued liabilities — 8,303 — Total current liabilities held for sale — 15,473 7,425 Noncurrent liabilities: Deferred income taxes (b) 55 — 14 Total noncurrent liabilities held for sale 55 — 14 Total liabilities held for sale $ 55 $ 15,473 $ 7,439 (a) On the Company's Consolidated Balance Sheets, this amount was reclassified to income taxes payable and is reflected in current liabilities held for sale. (b) On the Company's Consolidated Balance Sheets, these amounts were reclassified to noncurrent deferred income tax assets and are reflected in noncurrent assets held for sale. In the first quarter of 2017, the Company recorded a reversal of a previously accrued liability of $7.0 million ( $4.3 million after tax) due to the resolution of a legal matter. At June 30, 2017 , Dakota Prairie Refining had not incurred any material exit and disposal costs, and does not expect to incur any material exit and disposal costs. The Company performed a fair value assessment of the assets and liabilities classified as held for sale. In the second quarter of 2016, the fair value assessment was determined using the market approach based on the sale transaction to Tesoro. The fair value assessment indicated an impairment based on the carrying value exceeding the fair value, which resulted in the Company recording an impairment of $251.9 million ( $156.7 million after tax) in the quarter ended June 30, 2016. The impairment was included in operating expenses from discontinued operations. The fair value of Dakota Prairie Refining’s assets has been categorized as Level 3 in the fair value hierarchy. 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 all of Fidelity's oil and natural gas assets. The completion of these sales occurred between October 2015 and April 2016. 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. The carrying amounts of the major classes of assets and liabilities that are classified as held for sale related to the operations of Fidelity on the Company's Consolidated Balance Sheets were as follows: June 30, 2017 June 30, 2016 December 31, 2016 (In thousands) Assets Current assets: Receivables, net $ 328 $ 8,207 $ 355 Income taxes receivable — 5,348 — Prepayments and other current assets — 4 — Total current assets held for sale 328 13,559 355 Noncurrent assets: Net property, plant and equipment 2,064 5,507 5,507 Deferred income taxes 74,013 104,726 91,098 Other 161 161 161 Less allowance for impairment of assets held for sale — 938 938 Total noncurrent assets held for sale 76,238 109,456 95,828 Total assets held for sale $ 76,566 $ 123,015 $ 96,183 Liabilities Current liabilities: Accounts payable $ 138 $ 456 $ 141 Taxes payable 7,171 — 19 (a) Accrued compensation — 1,459 — Other accrued liabilities 2,724 10,849 2,358 Total current liabilities held for sale 10,033 12,764 2,518 Total liabilities held for sale $ 10,033 $ 12,764 $ 2,518 (a) On the Company's Consolidated Balance Sheets, this amount was reclassified to prepayments and other current assets and is reflected in current assets held for sale. The Company reclassified current income tax assets of $47.5 million and current income tax liabilities of $4.1 million to noncurrent assets - deferred income taxes at June 30, 2016, pursuant to the retrospective application of the adoption of the ASU related to the balance sheet classification of deferred taxes. For more information on this ASU, see Note 6 . The Company performed a fair value assessment of the assets and liabilities classified as held for sale. In the second quarter of 2016, the fair value assessment was determined using the income and market approaches. The income approach was determined by using the present value of future estimated cash flows. The market approach was based on market transactions of similar properties. The estimated carrying value exceeded the fair value and the Company recorded an impairment of $900,000 ( $600,000 after tax) in the second quarter of 2016. In the first quarter of 2016, the fair value assessment was determined using the market approach largely based on a purchase and sale agreement. The estimated fair value exceeded the carrying value and the Company recorded an impairment reversal of $1.4 million ( $900,000 after tax) in the first quarter of 2016. The impairment and impairment reversal were included in operating expenses from discontinued operations. The estimated fair value of Fidelity's assets have been categorized as Level 3 in the fair value hierarchy. The Company incurred transaction costs of approximately $300,000 in the first quarter of 2016. In addition to the transaction costs, and due in part to the change in plans to sell the assets of Fidelity rather than sell Fidelity as a company, Fidelity incurred and expensed approximately $3.8 million and $5.6 million of exit and disposal costs for the three and six months ended June 30, 2016 , respectively, and has incurred $10.5 million of exit and disposal costs to date. Fidelity incurred no exit and disposal costs for the three and six months ended June 30, 2017 , and the Company does not expect to incur any additional material exit and disposal costs. The exit and disposal costs are associated with severance and other related matters and exclude the office lease expiration discussed in the following paragraph. Fidelity vacated its office space in Denver, Colorado in 2016. The Company incurred lease payments of approximately $400,000 and $900,000 for the three and six months ended June 30, 2016 , respectively. A lease termination payment of $3.2 million was made during the second quarter of 2016. Existing office furniture and fixtures were relinquished to the lessor in the second quarter of 2016. Dakota Prairie Refining and Fidelity The reconciliation of the major classes of income and expense constituting pretax income (loss) from discontinued operations, which includes Dakota Prairie Refining and Fidelity, to the after-tax loss from discontinued operations on the Company's Consolidated Statements of Income was as follows: Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 (In thousands) Operating revenues $ 130 $ 74,756 $ 235 $ 122,732 Operating expenses 1,205 443,756 (5,372 ) 513,526 Operating income (loss) (1,075 ) (369,000 ) 5,607 (390,794 ) Other income (expense) 3 183 (13 ) 387 Interest expense 239 832 239 1,753 Income (loss) from discontinued operations before income taxes (1,311 ) (369,649 ) 5,355 (392,160 ) Income taxes 1,879 (93,547 ) 6,859 (98,022 ) Loss from discontinued operations (3,190 ) (276,102 ) (1,504 ) (294,138 ) Loss from discontinued operations attributable to noncontrolling interest — (120,651 ) — (131,691 ) Loss from discontinued operations attributable to the Company $ (3,190 ) $ (155,451 ) $ (1,504 ) $ (162,447 ) The pretax income (loss) from discontinued operations attributable to the Company, related to the operations of and activity associated with Dakota Prairie Refining, were $0 and $(244.0) million for the three months ended and $6.9 million and $(253.9) million for the six months ended June 30, 2017 and 2016 , respectively.

Goodwill and other intangible a

Goodwill and other intangible assets	6 Months Ended
	Jun. 30, 2017
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, 2017 Balance at January 1, 2017 Goodwill Acquired Balance at June 30, 2017 (In thousands) Natural gas distribution $ 345,736 $ — $ 345,736 Construction materials and contracting 176,290 — 176,290 Construction services 109,765 — 109,765 Total $ 631,791 $ — $ 631,791 Six Months Ended June 30, 2016 Balance at January 1, 2016 * Goodwill Acquired During the Year Balance at June 30, 2016 * (In thousands) Natural gas distribution $ 345,736 $ — $ 345,736 Pipeline and midstream 9,737 — 9,737 Construction materials and contracting 176,290 — 176,290 Construction services 103,441 6,323 109,764 Total $ 635,204 $ 6,323 $ 641,527 * Balance is presented net of accumulated impairment of $12.3 million at the pipeline and midstream segment, which occurred in prior periods. Year Ended December 31, 2016 Balance at January 1, 2016 * Goodwill Acquired During the Year Held for Sale Balance at December 31, 2016 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Pipeline and midstream 9,737 — (9,737 ) — Construction materials and contracting 176,290 — — 176,290 Construction services 103,441 6,324 — 109,765 Total $ 635,204 $ 6,324 $ (9,737 ) $ 631,791 * Balance is presented net of accumulated impairment of $12.3 million at the pipeline and midstream segment, which occurred in prior periods. Other amortizable intangible assets were as follows: June 30, 2017 June 30, 2016 December 31, 2016 (In thousands) Customer relationships $ 15,745 $ 17,145 $ 17,145 Less accumulated amortization 13,302 13,108 13,917 2,443 4,037 3,228 Noncompete agreements 2,430 2,430 2,430 Less accumulated amortization 1,732 1,585 1,658 698 845 772 Other 7,086 7,764 7,768 Less accumulated amortization 5,442 5,486 5,843 1,644 2,278 1,925 Total $ 4,785 $ 7,160 $ 5,925 Amortization expense for amortizable intangible assets for the three and six months ended June 30, 2017 , was $600,000 and $1.2 million , respectively. Amortization expense for amortizable intangible assets for the three and six months ended June 30, 2016, was $600,000 and $1.3 million , respectively. Estimated amortization expense for amortizable intangible assets is $2.2 million in 2017 , $1.2 million in 2018 , $1.0 million in 2019 , $500,000 in 2020 , $200,000 in 2021 and $800,000 thereafter.

Fair value measurements

Fair value measurements	6 Months Ended
	Jun. 30, 2017
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 $73.1 million , $71.4 million and $70.9 million , at June 30, 2017 and 2016 , and December 31, 2016 , respectively, are classified as investments on the Consolidated Balance Sheets. The net unrealized gains on these investments were $2.1 million and $5.0 million for the three and six months ended June 30, 2017 . The net unrealized gains on these investments were $2.3 million and $3.9 million for the three and six months ended June 30, 2016 . The change in fair value, which is considered part of the cost of the plan, is classified in operation and maintenance expense on the Consolidated Statements of Income. The Company did not elect the fair value option, which records gains and losses in income, for its available-for-sale securities, which include mortgage-backed securities and U.S. Treasury securities. These available-for-sale securities are recorded at fair value and are classified as investments on the Consolidated Balance Sheets. Unrealized gains or losses are recorded in accumulated other comprehensive income (loss). Details of available-for-sale securities were as follows: June 30, 2017 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 9,743 $ 13 $ (86 ) $ 9,670 U.S. Treasury securities 613 — — 613 Total $ 10,356 $ 13 $ (86 ) $ 10,283 June 30, 2016 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,420 $ 52 $ (12 ) $ 10,460 Total $ 10,420 $ 52 $ (12 ) $ 10,460 December 31, 2016 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,546 $ 8 $ (105 ) $ 10,449 Total $ 10,546 $ 8 $ (105 ) $ 10,449 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 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, 2017 and 2016 , 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, 2017, 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, 2017 (In thousands) Assets: Money market funds $ — $ 5,882 $ — $ 5,882 Insurance contract* — 73,126 — 73,126 Available-for-sale securities: Mortgage-backed securities — 9,670 — 9,670 U.S. Treasury securities — 613 — 613 Total assets measured at fair value $ — $ 89,291 $ — $ 89,291 * The insurance contract invests approximately 50 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, 2 percent in target date investments and 1 percent in cash equivalents. Fair Value Measurements at June 30, 2016, 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, 2016 (In thousands) Assets: Money market funds $ — $ 1,525 $ — $ 1,525 Insurance contract* — 71,355 — 71,355 Available-for-sale securities: Mortgage-backed securities — 10,460 — 10,460 Total assets measured at fair value $ — $ 83,340 $ — $ 83,340 * The insurance contract invests approximately 66 percent in fixed-income investments, 17 percent in common stock of large-cap companies, 9 percent in common stock of mid-cap companies, 6 percent in common stock of small-cap companies, 1 percent in target date investments and 1 percent in cash equivalents. Fair Value Measurements at December 31, 2016, 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, 2016 (In thousands) Assets: Money market funds $ — $ 1,602 $ — $ 1,602 Insurance contract* — 70,921 — 70,921 Available-for-sale securities: Mortgage-backed securities — 10,449 — 10,449 Total assets measured at fair value $ — $ 82,972 $ — $ 82,972 * The insurance contract invests approximately 52 percent in fixed-income investments, 22 percent in common stock of large-cap companies, 13 percent in common stock of mid-cap companies, 10 percent in common stock of small-cap companies, 1 percent in target date investments and 2 percent in cash equivalents. For information about fair value assessments of assets and liabilities classified as held for sale, see Note 8 . 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, 2017 $ 1,761,476 $ 1,864,884 Long-term debt at June 30, 2016 $ 1,987,307 $ 2,134,708 Long-term debt at December 31, 2016 $ 1,790,159 $ 1,841,885 The carrying amounts of the Company's remaining financial instruments included in current assets and current liabilities approximate their fair values .

Equity

Equity	6 Months Ended
	Jun. 30, 2017
Equity [Abstract]
Equity	Equity A summary of the changes in equity was as follows: Six Months Ended June 30, 2017 Total Equity (In thousands) Balance at December 31, 2016 $ 2,316,244 Net income 78,539 Other comprehensive loss (56 ) Dividends declared on preferred stocks (171 ) Dividends declared on common stock (75,192 ) Stock-based compensation 1,629 Repurchase of common stock (1,684 ) Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (757 ) Redemption of preferred stock (15,600 ) Balance at June 30, 2017 $ 2,302,952 Effective April 1, 2017, all outstanding preferred stock, including $300,000 of redeemable preferred stock classified as long-term debt, was redeemed for a repurchase price of approximately $15.9 million . Six Months Ended June 30, 2016 Total Stockholders' Equity Noncontrolling Interest Total Equity (In thousands) Balance at December 31, 2015 $ 2,396,505 $ 124,043 $ 2,520,548 Net loss (84,283 ) (131,691 ) (215,974 ) Other comprehensive loss (1,058 ) — (1,058 ) Dividends declared on preferred stocks (343 ) — (343 ) Dividends declared on common stock (73,239 ) — (73,239 ) Stock-based compensation 2,015 — 2,015 Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (323 ) — (323 ) Net tax deficit on stock-based compensation (1,664 ) — (1,664 ) Contribution from noncontrolling interest — 7,648 7,648 Balance at June 30, 2016 $ 2,237,610 $ — $ 2,237,610

Cash flow information

Cash flow information	6 Months Ended
	Jun. 30, 2017
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, 2017 2016 (In thousands) Interest, net of amount capitalized and AFUDC - borrowed of $418 and $548 in 2017 and 2016, respectively $ 39,207 $ 44,860 Income taxes paid, net* $ 32,388 $ 29,891 * Income taxes refunded, net of discontinued operations, were $ (3.6) million and $ (500,000) for the six months ended June 30, 2017 and 2016, respectively. Noncash investing transactions were as follows: June 30, 2017 2016 (In thousands) Property, plant and equipment additions in accounts payable $ 10,449 $ 18,449

Business segment data

Business segment data	6 Months Ended
	Jun. 30, 2017
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. For information on the Company's natural gas and oil gathering and processing facility sold on January 1, 2017, see Note 8 . The construction materials and contracting segment mines aggregates and markets crushed stone, sand, gravel and related construction materials, including ready-mixed concrete, cement, asphalt, liquid asphalt and other value-added products. It also performs integrated contracting services. This segment operates in the central, southern and western United States and Alaska and Hawaii. The construction services segment provides utility construction services specializing in constructing and maintaining electric and communication lines, gas pipelines, fire suppression systems, and external lighting and traffic signalization. This segment also provides utility excavation and inside electrical and mechanical services, and manufactures and distributes transmission line construction equipment and other supplies. The Other category includes the activities of Centennial Capital, which 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 deductible layers of the insured companies' general liability, automobile liability, pollution liability and other coverages. Centennial Capital also owns certain real and personal property. The Other category also includes certain general and administrative costs (reflected in operation and maintenance expense) and interest expense which were previously allocated to the refining business and Fidelity and do not meet the criteria for income (loss) from discontinued operations. The Other category also includes Centennial Resources' former investment in Brazil. Discontinued operations includes the results and supporting activities of Dakota Prairie Refining and Fidelity other than certain general and administrative costs and interest expense as described above. Dakota Prairie Refining refined crude oil and produced and sold diesel fuel, naphtha, ATBs and other by-products of the production process. In the second quarter of 2016, the Company sold all of the outstanding membership interests in Dakota Prairie Refining. Fidelity engaged in oil and natural gas development and production activities in the Rocky Mountain and Mid-Continent/Gulf States regions of the United States. Between September 2015 and March 2016, the Company entered into purchase and sale agreements to sell all of Fidelity's oil and natural gas assets. The completion of these sales occurred between October 2015 and April 2016. For more information on discontinued operations, see Note 8 . The information below follows the same accounting policies as described in Note 1 of the Company's Notes to Consolidated Financial Statements in the 2016 Annual Report. Information on the Company's businesses was as follows: Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 (In thousands) External operating revenues: Regulated operations: Electric $ 74,574 $ 73,832 $ 162,799 $ 156,755 Natural gas distribution 131,592 112,770 474,111 412,165 Pipeline and midstream 19,319 19,450 22,190 22,998 225,485 206,052 659,100 591,918 Nonregulated operations: Pipeline and midstream 4,520 10,268 8,163 18,966 Construction materials and contracting 501,426 541,257 702,203 751,108 Construction services 336,009 285,924 635,580 541,424 Other 199 447 519 747 842,154 837,896 1,346,465 1,312,245 Total external operating revenues $ 1,067,639 $ 1,043,948 $ 2,005,565 $ 1,904,163 Intersegment operating revenues: Regulated operations: Electric $ — $ — $ — $ — Natural gas distribution — — — — Pipeline and midstream 6,353 6,594 27,841 27,691 6,353 6,594 27,841 27,691 Nonregulated operations: Pipeline and midstream 59 36 93 119 Construction materials and contracting 172 97 258 215 Construction services 295 77 301 539 Other 1,758 1,669 3,501 3,338 2,284 1,879 4,153 4,211 Intersegment eliminations (8,637 ) (8,473 ) (31,994 ) (31,902 ) Total intersegment operating revenues $ — $ — $ — $ — Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 (In thousands) Earnings (loss) on common stock: Regulated operations: Electric $ 7,859 $ 8,022 $ 22,191 $ 19,141 Natural gas distribution (2,797 ) (7,777 ) 25,064 17,464 Pipeline and midstream 5,492 5,564 10,048 10,852 10,554 5,809 57,303 47,457 Nonregulated operations: Pipeline and midstream (238 ) 737 (865 ) 739 Construction materials and contracting 21,168 33,696 1,255 19,225 Construction services 12,391 6,990 19,753 12,964 Other (2,163 ) (1,105 ) (2,440 ) (2,564 ) 31,158 40,318 17,703 30,364 Intersegment eliminations* 2,093 — 4,266 — Earnings on common stock before loss from discontinued operations 43,805 46,127 79,272 77,821 Loss from discontinued operations, net of tax* (3,190 ) (276,102 ) (1,504 ) (294,138 ) Loss from discontinued operations attributable to noncontrolling interest — (120,651 ) — (131,691 ) Total earnings (loss) on common stock $ 40,615 $ (109,324 ) $ 77,768 $ (84,626 ) * Includes eliminations for the presentation of income tax adjustments between continuing and discontinued operations.

Employee benefit plans

Employee benefit plans	6 Months Ended
	Jun. 30, 2017
Retirement Benefits [Abstract]
Pension and other postretirement benefit plans	Employee benefit plans Pension and other postretirement plans The Company has noncontributory 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, 2017 2016 2017 2016 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 306 $ 374 Interest cost 4,089 4,220 825 895 Expected return on assets (5,234 ) (5,182 ) (1,175 ) (1,118 ) Amortization of prior service credit — — (343 ) (343 ) Amortization of net actuarial loss 1,385 1,514 100 299 Net periodic benefit cost (credit), including amount capitalized 240 552 (287 ) 107 Less amount capitalized 73 121 (114 ) 4 Net periodic benefit cost (credit) $ 167 $ 431 $ (173 ) $ 103 Pension Benefits Other Postretirement Benefits Six Months Ended June 30, 2017 2016 2017 2016 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 753 $ 824 Interest cost 8,103 8,610 1,633 1,844 Expected return on assets (10,263 ) (10,462 ) (2,320 ) (2,267 ) Amortization of prior service credit — — (686 ) (686 ) Amortization of net actuarial loss 3,178 3,107 436 747 Net periodic benefit cost (credit), including amount capitalized 1,018 1,255 (184 ) 462 Less amount capitalized 180 202 (153 ) 38 Net periodic benefit cost (credit) $ 838 $ 1,053 $ (31 ) $ 424 Nonqualified benefit plans In addition to the qualified plan defined pension benefits reflected in the table, the Company also has unfunded, nonqualified benefit plans for executive officers and certain key management employees that generally provide for defined benefit payments at age 65 following the employee's retirement or, upon death, to their beneficiaries for a 15-year period. In February 2016, the Company froze the unfunded, nonqualified defined benefit plans to new participants and eliminated benefit increases. Vesting for participants not fully vested was retained. The Company's net periodic benefit cost for these plans for the three and six months ended June 30, 2017 , was $1.1 million and $2.3 million , respectively. The Company's net periodic benefit cost for these plans for the three months ended June 30, 2016 , was $1.2 million . The Company's net periodic benefit credit for these plans for the six months ended June 30, 2016, was $700,000 , which reflects a curtailment gain of $3.3 million in the first quarter of 2016.

Regulatory matters

Regulatory matters	6 Months Ended
	Jun. 30, 2017
Regulated Operations [Abstract]
Regulatory matters	Regulatory matters On June 10, 2016, Montana-Dakota filed an application for an increase in electric rates with the WYPSC. Montana-Dakota requested an increase of approximately $3.2 million annually or approximately 13.1 percent above current rates to recover Montana-Dakota's increased investment in facilities along with additional depreciation, operation and maintenance expenses including increased fuel costs, and taxes associated with the increases in investment. On December 28, 2016, Montana-Dakota and the interveners of the case filed a stipulation and agreement reflecting an increase of approximately $2.7 million annually or approximately 11.1 percent above current rates. On April 6, 2017, the WYPSC issued a final order approving the stipulation and agreement with rates effective with service rendered on and after March 1, 2017. On August 12, 2016, Intermountain filed an application with the IPUC for a natural gas rate increase of approximately $10.2 million annually or approximately 4.1 percent above current rates. The request includes rate recovery associated with increased investment in facilities and increased operating expenses. On January 17, 2017, Intermountain provided the IPUC with an updated revenue request of approximately $9.4 million . On April 28, 2017, the IPUC issued an order approving an increase of approximately $4.1 million or approximately 1.6 percent above current rates based on a 9.5 percent return on equity effective with service rendered on and after May 1, 2017. On May 18, 2017, Intermountain filed a petition for reconsideration with the IPUC requesting the reconsideration of certain items denied in the April 28 order. On June 15, 2017, the IPUC granted the request for reconsideration. The IPUC has 13 weeks to complete the reconsideration and until the middle of September 2017 to issue a final order of reconsideration. On December 2, 2016, Montana-Dakota filed an application with the MTPSC requesting authority to implement gas and electric tax tracking adjustments for Montana state and local taxes and fees that reflect the changes in state and local property taxes applicable to natural gas and electric utilities pursuant to Montana law. The requested tax tracking adjustments would result in an increase in revenues of approximately $814,000 . On January 17, 2017, the MTPSC issued an order on the tax tracking adjustments. The gas tracking adjustment was approved as an increase to revenues of approximately $474,000 effective January 1, 2017. The electric tax tracking adjustment was approved as an increase to revenues of approximately $251,000 effective May 15, 2017. Montana-Dakota filed a motion for reconsideration of the electric tax tracking adjustment on January 27, 2017. On May 30, 2017, the MTPSC granted Montana-Dakota's motion for reconsideration allowing the full amount of electric taxes covered in the stipulated tariffs to be recovered. The additional revenues of approximately $88,000 will be included in a true-up to be effective in 2018. On December 21, 2016, Great Plains filed an application with the MNPUC requesting authority to implement a natural gas utility infrastructure cost tariff of approximately $456,000 annually effective beginning with service rendered May 20, 2017. The tariff will allow Great Plains to recover infrastructure investments, not previously included in rates, mandated by federal or state agencies associated with Great Plains' pipeline integrity programs. This matter is pending before the MNPUC. On April 1, 2017, Montana-Dakota implemented Phase 2 of the electric rate case approved by the MTPSC on March 25, 2016. The annual increase of $4.7 million is effective with service rendered on and after April 1, 2017. On May 31, 2017, Cascade filed an application with the WUTC for an annual pipeline replacement cost recovery mechanism of approximately $1.6 million or approximately .75 percent of additional revenue. The requested increase includes incremental pipeline replacement investments associated with qualifying pipeline integrity projects. If approved, rates will be effective November 1, 2017. This matter is pending before the WUTC. On June 30, 2017, Montana-Dakota filed an application for advance determination of prudence and a certificate of public convenience and necessity with the NDPSC to purchase an expansion of the Thunder Spirit Wind farm. The advance determination of prudence would provide Montana-Dakota with assurance that the project is prudent and in the best interest of the public and assists in the recovery of Montana-Dakota's investment upon completion of the project. The expansion is expected to serve customers by the end of 2018 and is estimated to cost approximately $85 million . On July 21, 2017, Montana-Dakota filed an application with the NDPSC for a natural gas rate increase of approximately $5.9 million annually or approximately 5.4 percent above current rates. The requested increase is primarily to recover the increased investment in distribution facilities to enhance system safety and reliability and the depreciation and taxes associated with the increase in investment. Montana-Dakota is also introducing a System Safety Integrity Program and the proposed adjustment mechanism required to fund the System Safety Integrity Program. Montana-Dakota has requested an interim increase of approximately $4.6 million or approximately 4.2 percent , subject to refund. This matter is pending before the NDPSC. On July 31, 2017, Cascade filed an application with the WUTC for a natural gas rate increase of approximately $5.9 million annually or approximately 2.7 percent above current rates. The requested increase includes costs associated with increased infrastructure investment and the associated operating expenses. Also included in the request is recovery of operation and maintenance costs associated with a maximum allowable operating pressure validation plan. This matter is pending before the WUTC. Montana-Dakota previously filed an application with the NDPSC on October 14, 2016, for an electric rate increase which also included a requested return on equity to be used in the determination of applications previously filed by Montana-Dakota for a renewable resource cost adjustment rider, an electric generation resource recovery rider, and a transmission cost adjustment rider, as discussed in the following paragraphs. On April 7, 2017, Montana-Dakota, the NDPSC Advocacy Staff and the interveners in the case filed a settlement agreement resolving all issues in the general rate case. The settlement agreement included a net increase of approximately $7.5 million or 3.7 percent above previously approved final rates and a true-up of the return on equity used in the interim renewable resource cost adjustment, the electric generation resource recovery and transmission cost adjustment riders of 9.45 percent; a return on equity of 9.65 percent for base rates and the renewable resource cost adjustment rider on a go-forward basis; and a return on equity of 9.45 percent through December 31, 2019, for the natural gas-fired internal combustion engines and associated facilities included in the electric generation resource recovery rider. A hearing on the settlement agreement was held on April 10, 2017. On June 16, 2017, the NDPSC approved the settlement agreement. On June 26, 2017, Montana-Dakota submitted a compliance filing and on July 14, 2017, submitted updated tariff sheets and a refund plan. The NDPSC approved the compliance filing and refund plan on July 26, 2017, with final rates effective with service rendered on or after August 7, 2017. The final rates are less than the interim rates currently in effect. Therefore, Montana-Dakota will refund the difference to customers, which is approximately 19 percent of the amount collected from the general rate case interim increase, along with refunds to reflect true-ups for the various riders, as applicable. The background information related to the settlement agreement and related applications are discussed in the following paragraphs. On October 26, 2015, Montana-Dakota filed an application with the NDPSC requesting a renewable resource cost adjustment rider for the recovery of the Thunder Spirit Wind project. On January 5, 2016, the NDPSC approved the rider to be effective January 7, 2016, resulting in an annual increase on an interim basis, subject to refund, of $15.1 million based upon a 10.5 percent return on equity to be finalized upon approval of the electric rate case filed on October 14, 2016. The electric rate case settlement agreement filed on April 7, 2017, included a revised return on equity for the rider. The settlement agreement was approved on June 16, 2017, as previously discussed in this note. On October 26, 2015, Montana-Dakota filed an application with the NDPSC for an update to the electric generation resource recovery rider. On March 9, 2016, the NDPSC approved the rider to be effective with service rendered on and after March 15, 2016, which resulted in interim rates, subject to refund, of $9.7 million based upon a 10.5 percent return on equity to be finalized upon the approval of the electric rate case filed on October 14, 2016. The interim rates include recovery of Montana-Dakota's investment in the 88-MW simple-cycle natural gas turbine and associated facilities near Mandan, North Dakota, and the 19 MW of new generation from natural gas-fired internal combustion engines and associated facilities near Sidney, Montana. The electric rate case settlement agreement filed on April 7, 2017, included the net investment authorized for the natural gas-fired internal combustion engines and the return on equity on both investments. The settlement agreement was approved on June 16, 2017, as previously discussed in this note. On November 25, 2015, Montana-Dakota filed an application with the NDPSC for an update of its transmission cost adjustment rider for recovery of MISO-related charges and two transmission projects in North Dakota. On February 10, 2016, the NDPSC approved the transmission cost adjustment effective with service rendered on and after February 12, 2016, resulting in an annual increase on an interim basis, subject to refund, of $6.8 million based upon a 10.5 percent return on equity to be finalized upon approval of the electric rate case filed on October 14, 2016. The electric rate case settlement agreement filed on April 7, 2017, included a revised return on equity for the rider. The settlement agreement was approved on June 16, 2017, as previously discussed in this note. On October 14, 2016, Montana-Dakota filed an application with the NDPSC for an electric rate increase of approximately $13.4 million annually or 6.6 percent above current rates. The request includes rate recovery associated with increased investment in facilities, along with the related depreciation, operation and maintenance expenses and taxes associated with the increased investment. Montana-Dakota requested an interim increase of approximately $13.0 million or approximately 6.5 percent, subject to refund, to be effective within 60 days of the filing. On November 21, 2016, Montana-Dakota filed and on November 30, 2016, the NDPSC approved a revised interim increase of approximately $11.7 million , based on adjustments accepted by the NDPSC, or approximately 5.8 percent above current rates, subject to refund, effective with service rendered on or after December 13, 2016. A settlement agreement was filed on April 7, 2017, and subsequently approved on June 16, 2017, as previously discussed in this note.

Contingencies

Contingencies	6 Months Ended
	Jun. 30, 2017
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 had accrued liabilities of $33.7 million , $27.4 million and $31.8 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, 2017 and 2016 , and December 31, 2016 , respectively, including amounts that may have been accrued for matters discussed in Litigation and 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 can’t 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. Litigation Construction Services Capital Electric provided employees in 2012 to perform work for a contractor on a project in Kansas. One of the Capital Electric employees was injured while working on the project and brought a lawsuit against the contractor. Judgment was entered in favor of the employee and his spouse on November 3, 2016, in the amount of $44.8 million following a court determination that the employee’s injuries were caused by the contractor’s negligence. The contractor claims that Capital Electric was contractually required, but failed, to name the contractor as an additional insured under any liability policy in effect at the time of the project and that such failure resulted in the entry of judgment against the contractor. In March 2017, Capital Electric filed a petition for declaratory judgment in the District Court of Wyandotte County, Kansas for a judicial determination that any agreement between Capital Electric and the contractor for the project did not require Capital Electric to include the contractor as an additional insured under any liability policy issued to Capital Electric and that if such an agreement was found to exist, it would be void and unenforceable under Kansas law. No accrual has been recorded for this matter. 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 a riverbed site adjacent to a commercial property site acquired by Knife River - Northwest from Georgia-Pacific West, Inc. in 1999. The riverbed site is part of the Portland, Oregon, Harbor Superfund Site. The EPA wants responsible parties to share in the cleanup of sediment contamination in the Willamette River. 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, a group of several entities, which does not include Knife River - Northwest or Georgia-Pacific West, Inc. Investigative costs are indicated to be in excess of $100 million . On January 6, 2017, Region 10 of the EPA issued a ROD with its selected remedy for cleanup of the in-river portion of the site. Implementation of the remedy 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 also received notice in January 2008 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. The Portland Harbor Natural Resource Trustee Council indicates the injury determination is appropriate to facilitate early settlement of damages and restoration for natural resource injuries. It is not possible to estimate the costs of natural resource damages until an assessment is completed and allocations are undertaken. Based upon a review of the Portland Harbor sediment contamination evaluation by the Oregon DEQ and other information available, Knife River - Northwest does not believe it is a responsible party. In addition, Knife River - Northwest 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. By letter in March 2009, LWG 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. The first claim is for contamination at a site in Eugene, Oregon which was received in 1995. There are PRPs in addition to Cascade that may be liable for cleanup of the contamination. Some of these PRPs have shared in the investigation costs. It is expected that these and other PRPs will share in the cleanup costs. The Oregon DEQ released a ROD in January 2015 that selected a remediation alternative for the site as recommended in an earlier staff report. The total estimated cost for the selected remediation, including long term maintenance, is approximately $3.5 million of which $320,000 has been incurred. It is not known at this time what share of the cleanup costs will actually be borne by Cascade; however, Cascade has paid 50 percent of the ongoing investigation and design costs and anticipates its proportional share of the final costs could be approximately 50 percent. Cascade has an accrual balance of $1.6 million for remediation 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 for the 12-month periods starting November 30, 2013, December 1, 2014, and December 1, 2015. Cascade has requested authority to defer accounting for the 12-month period starting December 1, 2016, which is pending before the OPUC. The second claim is for contamination at a 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 $200,000 has been incurred. Cascade has accrued $7.4 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, which are included in other noncurrent assets, 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 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. The notice indicates that current estimates to complete investigation and cleanup of the site exceed $8.0 million . Other PRPs have reached an agreed order and work plan with the Washington DOE for completion of a remedial investigation and feasibility study for the site. A report documenting the initial phase of the remedial investigation was completed in June 2011. There is currently not enough information available to estimate the potential liability to Cascade associated with this claim although 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 not recorded an accrual for this site. Cascade has received notices from and entered into agreement with certain of its insurance carriers that they will participate in defense of Cascade for these 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. The accruals related to these matters are reflected in regulatory assets. Guarantees In June 2016, WBI Energy sold all of the outstanding membership interests in Dakota Prairie Refining. In connection with the sale, Centennial agreed to continue to guarantee certain debt obligations of Dakota Prairie Refining which totaled $58.5 million at June 30, 2017 , and are expected to mature by 2023. Tesoro agreed to indemnify Centennial for any losses and litigation expenses arising from the guarantee. The estimated fair values of the indemnity asset and guarantee liability are reflected in deferred charges and other assets - other and deferred credits and other liabilities - other, respectively, on the Consolidated Balance Sheets. Continuation of the guarantee was required as a condition to the sale of Dakota Prairie Refining. In March 2016, a sale agreement was signed to sell Fidelity's assets in the Paradox Basin. In connection with the sale, Centennial agreed to guarantee Fidelity's indemnity obligations associated with the Paradox assets. The guarantee was required by the buyer as a condition to the sale of the Paradox Basin assets. 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, 2017 , the fixed maximum amounts guaranteed under these agreements aggregated $106.2 million . The amounts of scheduled expiration of the maximum amounts guaranteed under these agreements aggregate $6.6 million in 2017 ; $24.8 million in 2018 ; $20.2 million in 2019 ; $47.4 million in 2020 ; $500,000 in 2021 ; $2.7 million thereafter; and $4.0 million , which has no scheduled maturity date. There were no amounts outstanding under the above guarantees at June 30, 2017 . 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, 2017 , the fixed maximum amounts guaranteed under these letters of credit aggregated $33.8 million . The amounts of scheduled expiration of the maximum amounts guaranteed under these letters of credit aggregate $33.1 million in 2017 and $700,000 in 2018. There were no amounts outstanding under the above letters of credit at June 30, 2017 . In the event of default under these letter of credit obligations, the subsidiary issuing the letter of credit for that particular obligation would be required to make payments under its 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 for these guarantees were reflected on the Consolidated Balance Sheet at June 30, 2017 . 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, 2017 , approximately $765.5 million of surety bonds were outstanding, which were not reflected on the Consolidated Balance Sheet. Variable interest entities The Company evaluates its arrangements and contracts with other entities to determine if they are VIEs and if so, if the Company is the primary beneficiary. Fuel Contract Coyote Station entered into a coal supply agreement with Coyote Creek that provides for the purchase of coal necessary to supply the coal requirements of the Coyote Station for 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 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, 2017 , 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 $42.1 million .

Basis of presentation (Policies

Basis of presentation (Policies)	6 Months Ended
	Jun. 30, 2017
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 2016 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. Management has also evaluated the impact of events occurring after June 30, 2017 , up to the date of issuance of these consolidated interim financial statements. 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 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. The Company's consolidated financial statements and accompanying notes for current and prior periods have been restated. 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.

Accounts receivable and allow25

Accounts receivable and allowance for doubtful accounts (Policies)	6 Months Ended
	Jun. 30, 2017
Receivables [Abstract]
Accounts receivable and allowance for doubtful accounts	Accounts receivable consist 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 i26

Inventories and natural gas in storage (Policies)	6 Months Ended
	Jun. 30, 2017
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 (loss) per common sh27

Earnings (loss) per common share (Policies)	6 Months Ended
	Jun. 30, 2017
Earnings Per Share [Abstract]
Earnings (loss) per common share	Basic earnings (loss) per common share were computed by dividing earnings (loss) on common stock by the weighted average number of shares of common stock outstanding during the applicable period. Diluted earnings (loss) per common share were computed by dividing earnings (loss) on common stock by the total of the weighted average number of shares of common stock outstanding during the applicable period, plus the effect of outstanding performance share awards. Common stock outstanding includes issued shares less shares held in treasury.

New accounting standards (Polic

New accounting standards (Policies)	6 Months Ended
	Jun. 30, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New accounting standards	Recently adopted accounting standards Balance Sheet Classification of Deferred Taxes In November 2015, the FASB issued guidance regarding the classification of deferred taxes on the balance sheet. The guidance requires all deferred tax assets and liabilities to be classified as noncurrent. These amendments align GAAP with IFRS. The Company adopted the guidance in the fourth quarter of 2016 and applied the retrospective method of adoption. The guidance required a reclassification of current deferred income taxes to noncurrent deferred income taxes on the Consolidated Balance Sheets, but did not impact the Company's results of operations or cash flows. As a result of the retrospective application of this change in accounting principle, the Company reclassified deferred income taxes of $33.9 million from current assets - deferred income taxes to deferred credits and other liabilities - deferred income taxes on its Consolidated Balance Sheet at June 30, 2016. Simplifying the Measurement of Inventory In July 2015, the FASB issued guidance regarding inventory that is measured using the first-in, first-out or average cost method. The guidance does not apply to inventory measured using the last-in, first-out or the retail inventory method. The guidance requires inventory within its scope to be measured at the lower of cost or net realizable value, which is the estimated selling price in the normal course of business less reasonably predictable costs of completion, disposal and transportation. These amendments more closely align GAAP with IFRS. The Company adopted the guidance on January 1, 2017, on a prospective basis. The guidance did not have a material effect on the Company's results of operations, financial position, cash flows or disclosures. Improvements to Employee Share-Based Payment Accounting In March 2016, the FASB issued guidance regarding simplification of several aspects of the accounting for share-based payment transactions. The guidance affects the income tax consequences, classification of awards as either equity or liabilities, classification on the statement of cash flows and calculation of dilutive shares. The Company adopted the guidance on January 1, 2017. All amendments in the guidance that apply to the Company were adopted on a prospective basis resulting in no adjustments being made to retained earnings. The adoption of the guidance impacted the Consolidated Statement of Income and the Consolidated Balance Sheet in the first quarter of 2017 due to the taxes related to the stock-based compensation award that vested in February 2017 being recognized as income tax expense as compared to a reduction to additional paid-in capital under the previous guidance. Adoption of the guidance also increased the number of shares included in the diluted earnings per share calculation due to the exclusion of tax benefits in the incremental shares calculation. The change in the weighted average common shares outstanding - diluted did not result in a material effect on the earnings per common share - diluted. Recently issued accounting standards not yet adopted Revenue from Contracts with Customers In May 2014, the FASB issued guidance on accounting for revenue from contracts with customers. The guidance provides for a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry specific guidance. In August 2015, the FASB issued guidance deferring the effective date of the revenue guidance and allowing entities to early adopt. With this decision, the guidance will be effective for the Company on January 1, 2018. Entities will have the option of using either a full retrospective or modified retrospective approach to adopting the guidance. The Company plans to adopt the guidance on January 1, 2018, and to use the modified retrospective approach. Under the modified approach, an entity would recognize the cumulative effect of initially applying the guidance with an adjustment to the opening balance of retained earnings in the period of adoption. In addition, the guidance will require expanded disclosures, both quantitative and qualitative, related to the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. The Company does not anticipate a significant change in the timing of revenue recognition and continues to evaluate all revenue streams to determine what effect the guidance will have on its results of operations, financial position, cash flows and disclosures. Recognition and Measurement of Financial Assets and Financial Liabilities In January 2016, the FASB issued guidance regarding the classification and measurement of financial instruments. The guidance revises the way an entity classifies and measures investments in equity securities, the presentation of certain fair value changes for financial liabilities measured at fair value and amends certain disclosure requirements related to the fair value of financial instruments. This guidance will be effective for the Company on January 1, 2018, with early adoption of certain amendments permitted. The guidance should be applied using a modified retrospective approach with the exception of equity securities without readily determinable fair values which will be applied prospectively. The Company is evaluating the effects the adoption of the new guidance will have on its results of operations, financial position, cash flows and disclosures. Classification of Certain Cash Receipts and Cash Payments In August 2016, the FASB issued guidance to clarify the classification of certain cash receipts and payments in the statement of cash flows. The guidance is intended to standardize the presentation and classification of certain transactions, including cash payments for debt prepayment or extinguishment, proceeds from insurance claim settlements and distributions from equity method investments. In addition, the guidance clarifies how to classify transactions that have characteristics of more than one class of cash flows. This guidance will be effective for the Company on January 1, 2018, with early adoption permitted. An entity that elects early adoption must adopt all the amendments in the same period and apply any adjustments as of the beginning of the fiscal year. Entities must apply the guidance retrospectively unless it is impracticable to do so, in which case they may apply it prospectively as of the earliest date practicable. The Company is evaluating the effects the adoption of the new guidance will have on its cash flows and disclosures. Clarifying the Definition of a Business In January 2017, the FASB issued guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions or disposals of assets or businesses. The guidance provides a screen to determine when an integrated set of assets and activities is not a business. The guidance will also affect other aspects of accounting, such as determining reporting units for goodwill testing and whether an entity has acquired or sold a business. The guidance will be effective for the Company on January 1, 2018, and should be applied on a prospective basis with early adoption permitted for transactions that occur before the issuance or effective date of the amendments and only when the transactions have not been reported in the financial statements or made available for issuance. The Company expects to adopt this guidance as required and does not expect the guidance to have a material effect on its results of operations, financial position, cash flows and disclosures. Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost In March 2017, the FASB issued guidance to improve the presentation of net periodic pension cost and net periodic postretirement benefit cost. The guidance requires the service cost component to be presented in the income statement in the same line item or items as other compensation costs arising from services performed during the period. Other components of net benefit cost shall be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. The guidance also only allows the service cost component to be capitalized. The guidance will be effective for the Company on January 1, 2018, including interim periods, with early adoption permitted as of the beginning of an annual period for which the financial statements have not been issued. The guidance shall be applied on a retrospective basis for the financial statement presentation and on a prospective basis for the capitalization of the service cost component. The Company is evaluating the effects the adoption of the new guidance will have on its results of operations, financial position, cash flows and disclosures. Leases In February 2016, the FASB issued guidance regarding leases. The guidance requires lessees to recognize a lease liability and a right-of-use asset on the balance sheet for operating and financing leases with terms of more than 12 months. The guidance remains 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 requires additional disclosures, both quantitative and qualitative, related to operating and finance leases for the lessee and sales-type, direct financing and operating leases for the lessor. This guidance will be effective for the Company on January 1, 2019, and should be applied using a modified retrospective approach with early adoption permitted. There continues to be industry-specific implementation issues that are unresolved and the final resolution of these issues could significantly impact the number of contracts that would be considered a lease for the Company under the new guidance. Due to the uncertainty of these issues, the Company cannot estimate the potential impact the adoption of the new guidance will have on its results of operations, financial position, cash flows and disclosures. The Company is planning to adopt the standard on January 1, 2019, utilizing the practical expedient that allows the Company to not reassess whether an expired or existing contract contains a lease, the classification of leases or initial direct costs. 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 should be applied on a prospective basis with early adoption permitted. The Company is evaluating the effects the adoption of the new guidance will have on its results of operations, financial position, cash flows and disclosures.

Fair value disclosures (Policie

Fair value disclosures (Policies)	6 Months Ended
	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Fair value measurements	The Company measures its investments in certain fixed-income and equity securities at fair value with changes in fair value recognized in income.
Investments	The Company did not elect the fair value option, which records gains and losses in income, for its available-for-sale securities, which include mortgage-backed securities and U.S. Treasury securities. These available-for-sale securities are recorded at fair value and are classified as investments on the Consolidated Balance Sheets.

Business segment data (Policies

Business segment data (Policies)	6 Months Ended
	Jun. 30, 2017
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, 2017
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 i32

Inventories and natural gas in storage (Tables)	6 Months Ended
	Jun. 30, 2017
Inventory Disclosure [Abstract]
Inventories	Inventories consisted of: June 30, 2017 June 30, 2016 December 31, 2016 (In thousands) Aggregates held for resale $ 123,316 $ 130,544 $ 115,471 Asphalt oil 46,852 42,591 29,103 Materials and supplies 22,657 20,765 18,372 Merchandise for resale 16,164 18,439 16,437 Natural gas in storage (current) 14,126 19,689 25,761 Other 26,755 33,821 33,129 Total $ 249,870 $ 265,849 $ 238,273

Earnings (loss) per common sh33

Earnings (loss) per common share (Tables)	6 Months Ended
	Jun. 30, 2017
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 (loss) per share calculations was as follows: Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 (In thousands) Weighted average common shares outstanding - basic 195,304 195,304 195,304 195,294 Effect of dilutive performance share awards 669 395 689 384 Weighted average common shares outstanding - diluted 195,973 195,699 195,993 195,678 Shares excluded from the calculation of diluted earnings per share — — — —

Comprehensive income (loss) (Ta

Comprehensive income (loss) (Tables)	6 Months Ended
	Jun. 30, 2017
Equity [Abstract]
Comprehensive income (loss)	The after-tax changes in the components of accumulated other comprehensive loss were as follows: Three Months Ended June 30, 2017 Net Unrealized Gain (Loss) on Derivative Instruments Qualifying as Hedges Postretirement Liability Adjustment Foreign Currency Translation Adjustment Net Unrealized Gain (Loss) on Available-for-sale Investments Total Accumulated Other Comprehensive Loss (In thousands) Balance at beginning of period $ (2,209 ) $ (33,781 ) $ (140 ) $ (55 ) $ (36,185 ) Other comprehensive loss before reclassifications — — (15 ) (24 ) (39 ) Amounts reclassified from accumulated other comprehensive loss 92 312 — 31 435 Net current-period other comprehensive income (loss) 92 312 (15 ) 7 396 Balance at end of period $ (2,117 ) $ (33,469 ) $ (155 ) $ (48 ) $ (35,789 ) Three Months Ended June 30, 2016 Net Unrealized Gain (Loss) on Derivative Instruments Qualifying as Hedges Postretirement Liability Adjustment Foreign Currency Translation Adjustment Net Unrealized Gain (Loss) on Available-for-sale Investments Total Accumulated Other Comprehensive Loss (In thousands) Balance at beginning of period $ (2,575 ) $ (35,852 ) $ (175 ) $ 20 $ (38,582 ) Other comprehensive income (loss) before reclassifications — — 31 (30 ) 1 Amounts reclassified from accumulated other comprehensive loss 91 248 — 36 375 Net current-period other comprehensive income 91 248 31 6 376 Balance at end of period $ (2,484 ) $ (35,604 ) $ (144 ) $ 26 $ (38,206 ) Six Months Ended June 30, 2017 Net Unrealized Gain (Loss) on Derivative Instruments Qualifying as Hedges Postretirement Liability Adjustment Foreign Currency Translation Adjustment Net Unrealized Gain (Loss) on Available-for-sale Investments Total Accumulated Other Comprehensive Loss (In thousands) Balance at beginning of period $ (2,300 ) $ (33,221 ) $ (149 ) $ (63 ) $ (35,733 ) Other comprehensive loss before reclassifications — — (6 ) (51 ) (57 ) Amounts reclassified from accumulated other comprehensive loss 183 669 — 66 918 Amounts reclassified to accumulated other comprehensive loss from a regulatory asset — (917 ) — — (917 ) Net current-period other comprehensive income (loss) 183 (248 ) (6 ) 15 (56 ) Balance at end of period $ (2,117 ) $ (33,469 ) $ (155 ) $ (48 ) $ (35,789 ) Six Months Ended June 30, 2016 Net Unrealized Gain (Loss) on Derivative Instruments Qualifying as Hedges Postretirement Liability Adjustment Foreign Currency Translation Adjustment Net Unrealized Gain (Loss) on Available-for-sale Investments Total Accumulated Other Comprehensive Loss (In thousands) Balance at beginning of period $ (2,667 ) $ (34,257 ) $ (200 ) $ (24 ) $ (37,148 ) Other comprehensive income (loss) before reclassifications — — 56 (19 ) 37 Amounts reclassified from accumulated other comprehensive loss 183 (1,347 ) — 69 (1,095 ) Net current-period other comprehensive income (loss) 183 (1,347 ) 56 50 (1,058 ) Balance at end of period $ (2,484 ) $ (35,604 ) $ (144 ) $ 26 $ (38,206 )
Reclassification out of accumulated other comprehensive income	Reclassifications out of accumulated other comprehensive loss were as follows: Three Months Ended Six Months Ended Location on Consolidated Statements of Income June 30, June 30, 2017 2016 2017 2016 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income (loss) $ (148 ) $ (147 ) $ (295 ) $ (297 ) Interest expense 56 56 112 114 Income taxes (92 ) (91 ) (183 ) (183 ) Amortization of postretirement liability gains (losses) included in net periodic benefit cost (credit) (502 ) (398 ) (1,075 ) 2,166 (a) 190 150 406 (819 ) Income taxes (312 ) (248 ) (669 ) 1,347 Reclassification adjustment for loss on available-for-sale investments included in net income (loss) (48 ) (55 ) (102 ) (106 ) Other income 17 19 36 37 Income taxes (31 ) (36 ) (66 ) (69 ) Total reclassifications $ (435 ) $ (375 ) $ (918 ) $ 1,095 (a) Included in net periodic benefit cost (credit). For more information, see Note 14 .

Assets held for sale and disc35

Assets held for sale and discontinued operations (Tables)	6 Months Ended
	Jun. 30, 2017
Discontinued Operations and Disposal Groups [Abstract]
Disclosure of long lived assets held-for-sale	The carrying amounts of the major classes of assets and liabilities that were classified as held for sale associated with Pronghorn on the Company's Consolidated Balance Sheets were as follows: December 31, 2016 (In thousands) Assets Current assets: Prepayments and other current assets $ 68 Total current assets held for sale 68 Noncurrent assets: Net property, plant and equipment 93,424 Goodwill 9,737 Less allowance for impairment of assets held for sale 2,311 Total noncurrent assets held for sale 100,850 Total assets held for sale $ 100,918
Disposal groups, including discontinued operations	The carrying amounts of the major classes of assets and liabilities that are classified as held for sale related to the operations of and activity associated with Dakota Prairie Refining on the Company's Consolidated Balance Sheets were as follows: June 30, 2017 June 30, 2016 December 31, 2016 (In thousands) Assets Current assets: Receivables, net $ — $ 433 $ — Income taxes receivable 5,552 (a) 12,550 13,987 Prepayments and other current assets — 11,083 — Total current assets held for sale 5,552 24,066 13,987 Noncurrent assets: Deferred income taxes — 57,644 — Total noncurrent assets held for sale — 57,644 — Total assets held for sale $ 5,552 $ 81,710 $ 13,987 Liabilities Current liabilities: Accounts payable $ — $ 7,170 $ 7,425 Other accrued liabilities — 8,303 — Total current liabilities held for sale — 15,473 7,425 Noncurrent liabilities: Deferred income taxes (b) 55 — 14 Total noncurrent liabilities held for sale 55 — 14 Total liabilities held for sale $ 55 $ 15,473 $ 7,439 (a) On the Company's Consolidated Balance Sheets, this amount was reclassified to income taxes payable and is reflected in current liabilities held for sale. (b) On the Company's Consolidated Balance Sheets, these amounts were reclassified to noncurrent deferred income tax assets and are reflected in noncurrent assets held for sale. The carrying amounts of the major classes of assets and liabilities that are classified as held for sale related to the operations of Fidelity on the Company's Consolidated Balance Sheets were as follows: June 30, 2017 June 30, 2016 December 31, 2016 (In thousands) Assets Current assets: Receivables, net $ 328 $ 8,207 $ 355 Income taxes receivable — 5,348 — Prepayments and other current assets — 4 — Total current assets held for sale 328 13,559 355 Noncurrent assets: Net property, plant and equipment 2,064 5,507 5,507 Deferred income taxes 74,013 104,726 91,098 Other 161 161 161 Less allowance for impairment of assets held for sale — 938 938 Total noncurrent assets held for sale 76,238 109,456 95,828 Total assets held for sale $ 76,566 $ 123,015 $ 96,183 Liabilities Current liabilities: Accounts payable $ 138 $ 456 $ 141 Taxes payable 7,171 — 19 (a) Accrued compensation — 1,459 — Other accrued liabilities 2,724 10,849 2,358 Total current liabilities held for sale 10,033 12,764 2,518 Total liabilities held for sale $ 10,033 $ 12,764 $ 2,518 (a) On the Company's Consolidated Balance Sheets, this amount was reclassified to prepayments and other current assets and is reflected in current assets held for sale.
Reconciliation of major classes of income and expense	The reconciliation of the major classes of income and expense constituting pretax income (loss) from discontinued operations, which includes Dakota Prairie Refining and Fidelity, to the after-tax loss from discontinued operations on the Company's Consolidated Statements of Income was as follows: Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 (In thousands) Operating revenues $ 130 $ 74,756 $ 235 $ 122,732 Operating expenses 1,205 443,756 (5,372 ) 513,526 Operating income (loss) (1,075 ) (369,000 ) 5,607 (390,794 ) Other income (expense) 3 183 (13 ) 387 Interest expense 239 832 239 1,753 Income (loss) from discontinued operations before income taxes (1,311 ) (369,649 ) 5,355 (392,160 ) Income taxes 1,879 (93,547 ) 6,859 (98,022 ) Loss from discontinued operations (3,190 ) (276,102 ) (1,504 ) (294,138 ) Loss from discontinued operations attributable to noncontrolling interest — (120,651 ) — (131,691 ) Loss from discontinued operations attributable to the Company $ (3,190 ) $ (155,451 ) $ (1,504 ) $ (162,447 )

Goodwill and other intangible36

Goodwill and other intangible assets (Tables)	6 Months Ended
	Jun. 30, 2017
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, 2017 Balance at January 1, 2017 Goodwill Acquired Balance at June 30, 2017 (In thousands) Natural gas distribution $ 345,736 $ — $ 345,736 Construction materials and contracting 176,290 — 176,290 Construction services 109,765 — 109,765 Total $ 631,791 $ — $ 631,791 Six Months Ended June 30, 2016 Balance at January 1, 2016 * Goodwill Acquired During the Year Balance at June 30, 2016 * (In thousands) Natural gas distribution $ 345,736 $ — $ 345,736 Pipeline and midstream 9,737 — 9,737 Construction materials and contracting 176,290 — 176,290 Construction services 103,441 6,323 109,764 Total $ 635,204 $ 6,323 $ 641,527 * Balance is presented net of accumulated impairment of $12.3 million at the pipeline and midstream segment, which occurred in prior periods. Year Ended December 31, 2016 Balance at January 1, 2016 * Goodwill Acquired During the Year Held for Sale Balance at December 31, 2016 (In thousands) Natural gas distribution $ 345,736 $ — $ — $ 345,736 Pipeline and midstream 9,737 — (9,737 ) — Construction materials and contracting 176,290 — — 176,290 Construction services 103,441 6,324 — 109,765 Total $ 635,204 $ 6,324 $ (9,737 ) $ 631,791 * Balance is presented net of accumulated impairment of $12.3 million at the pipeline and midstream segment, which occurred in prior periods.
Other amortizable intangible assets	Other amortizable intangible assets were as follows: June 30, 2017 June 30, 2016 December 31, 2016 (In thousands) Customer relationships $ 15,745 $ 17,145 $ 17,145 Less accumulated amortization 13,302 13,108 13,917 2,443 4,037 3,228 Noncompete agreements 2,430 2,430 2,430 Less accumulated amortization 1,732 1,585 1,658 698 845 772 Other 7,086 7,764 7,768 Less accumulated amortization 5,442 5,486 5,843 1,644 2,278 1,925 Total $ 4,785 $ 7,160 $ 5,925

Fair value measurements (Tables

Fair value measurements (Tables)	6 Months Ended
	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Available-for-sale securities	Details of available-for-sale securities were as follows: June 30, 2017 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 9,743 $ 13 $ (86 ) $ 9,670 U.S. Treasury securities 613 — — 613 Total $ 10,356 $ 13 $ (86 ) $ 10,283 June 30, 2016 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,420 $ 52 $ (12 ) $ 10,460 Total $ 10,420 $ 52 $ (12 ) $ 10,460 December 31, 2016 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 10,546 $ 8 $ (105 ) $ 10,449 Total $ 10,546 $ 8 $ (105 ) $ 10,449
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, 2017, 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, 2017 (In thousands) Assets: Money market funds $ — $ 5,882 $ — $ 5,882 Insurance contract* — 73,126 — 73,126 Available-for-sale securities: Mortgage-backed securities — 9,670 — 9,670 U.S. Treasury securities — 613 — 613 Total assets measured at fair value $ — $ 89,291 $ — $ 89,291 * The insurance contract invests approximately 50 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, 2 percent in target date investments and 1 percent in cash equivalents. Fair Value Measurements at June 30, 2016, 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, 2016 (In thousands) Assets: Money market funds $ — $ 1,525 $ — $ 1,525 Insurance contract* — 71,355 — 71,355 Available-for-sale securities: Mortgage-backed securities — 10,460 — 10,460 Total assets measured at fair value $ — $ 83,340 $ — $ 83,340 * The insurance contract invests approximately 66 percent in fixed-income investments, 17 percent in common stock of large-cap companies, 9 percent in common stock of mid-cap companies, 6 percent in common stock of small-cap companies, 1 percent in target date investments and 1 percent in cash equivalents. Fair Value Measurements at December 31, 2016, 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, 2016 (In thousands) Assets: Money market funds $ — $ 1,602 $ — $ 1,602 Insurance contract* — 70,921 — 70,921 Available-for-sale securities: Mortgage-backed securities — 10,449 — 10,449 Total assets measured at fair value $ — $ 82,972 $ — $ 82,972 * The insurance contract invests approximately 52 percent in fixed-income investments, 22 percent in common stock of large-cap companies, 13 percent in common stock of mid-cap companies, 10 percent in common stock of small-cap companies, 1 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, 2017 $ 1,761,476 $ 1,864,884 Long-term debt at June 30, 2016 $ 1,987,307 $ 2,134,708 Long-term debt at December 31, 2016 $ 1,790,159 $ 1,841,885

Equity (Tables)

Equity (Tables)	6 Months Ended
	Jun. 30, 2017
Equity [Abstract]
Summary of changes in equity	A summary of the changes in equity was as follows: Six Months Ended June 30, 2017 Total Equity (In thousands) Balance at December 31, 2016 $ 2,316,244 Net income 78,539 Other comprehensive loss (56 ) Dividends declared on preferred stocks (171 ) Dividends declared on common stock (75,192 ) Stock-based compensation 1,629 Repurchase of common stock (1,684 ) Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (757 ) Redemption of preferred stock (15,600 ) Balance at June 30, 2017 $ 2,302,952 Effective April 1, 2017, all outstanding preferred stock, including $300,000 of redeemable preferred stock classified as long-term debt, was redeemed for a repurchase price of approximately $15.9 million . Six Months Ended June 30, 2016 Total Stockholders' Equity Noncontrolling Interest Total Equity (In thousands) Balance at December 31, 2015 $ 2,396,505 $ 124,043 $ 2,520,548 Net loss (84,283 ) (131,691 ) (215,974 ) Other comprehensive loss (1,058 ) — (1,058 ) Dividends declared on preferred stocks (343 ) — (343 ) Dividends declared on common stock (73,239 ) — (73,239 ) Stock-based compensation 2,015 — 2,015 Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (323 ) — (323 ) Net tax deficit on stock-based compensation (1,664 ) — (1,664 ) Contribution from noncontrolling interest — 7,648 7,648 Balance at June 30, 2016 $ 2,237,610 $ — $ 2,237,610

Cash flow information (Tables)

Cash flow information (Tables)	6 Months Ended
	Jun. 30, 2017
Supplemental Cash Flow Information [Abstract]
Supplemental cash flow information	Cash expenditures for interest and income taxes were as follows: Six Months Ended June 30, 2017 2016 (In thousands) Interest, net of amount capitalized and AFUDC - borrowed of $418 and $548 in 2017 and 2016, respectively $ 39,207 $ 44,860 Income taxes paid, net* $ 32,388 $ 29,891 * Income taxes refunded, net of discontinued operations, were $ (3.6) million and $ (500,000) for the six months ended June 30, 2017 and 2016, respectively. Noncash investing transactions were as follows: June 30, 2017 2016 (In thousands) Property, plant and equipment additions in accounts payable $ 10,449 $ 18,449

Business segment data (Tables)

Business segment data (Tables)	6 Months Ended
	Jun. 30, 2017
Segment Reporting [Abstract]
Information on the Company's businesses	Information on the Company's businesses was as follows: Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 (In thousands) External operating revenues: Regulated operations: Electric $ 74,574 $ 73,832 $ 162,799 $ 156,755 Natural gas distribution 131,592 112,770 474,111 412,165 Pipeline and midstream 19,319 19,450 22,190 22,998 225,485 206,052 659,100 591,918 Nonregulated operations: Pipeline and midstream 4,520 10,268 8,163 18,966 Construction materials and contracting 501,426 541,257 702,203 751,108 Construction services 336,009 285,924 635,580 541,424 Other 199 447 519 747 842,154 837,896 1,346,465 1,312,245 Total external operating revenues $ 1,067,639 $ 1,043,948 $ 2,005,565 $ 1,904,163 Intersegment operating revenues: Regulated operations: Electric $ — $ — $ — $ — Natural gas distribution — — — — Pipeline and midstream 6,353 6,594 27,841 27,691 6,353 6,594 27,841 27,691 Nonregulated operations: Pipeline and midstream 59 36 93 119 Construction materials and contracting 172 97 258 215 Construction services 295 77 301 539 Other 1,758 1,669 3,501 3,338 2,284 1,879 4,153 4,211 Intersegment eliminations (8,637 ) (8,473 ) (31,994 ) (31,902 ) Total intersegment operating revenues $ — $ — $ — $ — Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 (In thousands) Earnings (loss) on common stock: Regulated operations: Electric $ 7,859 $ 8,022 $ 22,191 $ 19,141 Natural gas distribution (2,797 ) (7,777 ) 25,064 17,464 Pipeline and midstream 5,492 5,564 10,048 10,852 10,554 5,809 57,303 47,457 Nonregulated operations: Pipeline and midstream (238 ) 737 (865 ) 739 Construction materials and contracting 21,168 33,696 1,255 19,225 Construction services 12,391 6,990 19,753 12,964 Other (2,163 ) (1,105 ) (2,440 ) (2,564 ) 31,158 40,318 17,703 30,364 Intersegment eliminations* 2,093 — 4,266 — Earnings on common stock before loss from discontinued operations 43,805 46,127 79,272 77,821 Loss from discontinued operations, net of tax* (3,190 ) (276,102 ) (1,504 ) (294,138 ) Loss from discontinued operations attributable to noncontrolling interest — (120,651 ) — (131,691 ) Total earnings (loss) on common stock $ 40,615 $ (109,324 ) $ 77,768 $ (84,626 ) * Includes eliminations for the presentation of income tax adjustments between continuing and discontinued operations.

Employee benefit plans (Tables)

Employee benefit plans (Tables)	6 Months Ended
	Jun. 30, 2017
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, 2017 2016 2017 2016 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 306 $ 374 Interest cost 4,089 4,220 825 895 Expected return on assets (5,234 ) (5,182 ) (1,175 ) (1,118 ) Amortization of prior service credit — — (343 ) (343 ) Amortization of net actuarial loss 1,385 1,514 100 299 Net periodic benefit cost (credit), including amount capitalized 240 552 (287 ) 107 Less amount capitalized 73 121 (114 ) 4 Net periodic benefit cost (credit) $ 167 $ 431 $ (173 ) $ 103 Pension Benefits Other Postretirement Benefits Six Months Ended June 30, 2017 2016 2017 2016 (In thousands) Components of net periodic benefit cost (credit): Service cost $ — $ — $ 753 $ 824 Interest cost 8,103 8,610 1,633 1,844 Expected return on assets (10,263 ) (10,462 ) (2,320 ) (2,267 ) Amortization of prior service credit — — (686 ) (686 ) Amortization of net actuarial loss 3,178 3,107 436 747 Net periodic benefit cost (credit), including amount capitalized 1,018 1,255 (184 ) 462 Less amount capitalized 180 202 (153 ) 38 Net periodic benefit cost (credit) $ 838 $ 1,053 $ (31 ) $ 424

Accounts receivable and allow42

Accounts receivable and allowance for doubtful accounts (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Receivables [Abstract]
Receivables past due 90 days or more	$ 32.7	$ 29.2	$ 31.7
Allowance for doubtful accounts receivable	$ 9.2	$ 10.5	$ 11

Inventories and natural gas i43

Inventories and natural gas in storage (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Inventory Disclosure [Abstract]
Aggregates held for resale	$ 123,316	$ 115,471	$ 130,544
Asphalt oil	46,852	29,103	42,591
Materials and supplies	22,657	18,372	20,765
Merchandise for resale	16,164	16,437	18,439
Natural gas in storage (current)	14,126	25,761	19,689
Other	26,755	33,129	33,821
Total	249,870	238,273	265,849
Natural gas in storage noncurrent	$ 49,500	$ 49,500	$ 49,100

Earnings (loss) per common sh44

Earnings (loss) per common share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	195,304	195,304	195,304	195,294
Effect of dilutive performance share awards	669	395	689	384
Weighted average common shares outstanding - diluted	195,973	195,699	195,993	195,678
Shares excluded from the calculation of diluted earnings per share	0	0	0	0

New accounting standards New ac

New accounting standards New accounting pronouncements (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclass from current assets - deferred income taxes to deferred credits and other liabilities	$ 668,239	$ 668,226	$ 666,601
Accounting Standards Update 2015-17 [Member] | Restatement adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclass from current assets - deferred income taxes to deferred credits and other liabilities			$ 33,900

Comprehensive income (loss) (De

Comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated other comprehensive income (loss) [Roll Forward]
Balance			$ 2,316,244	$ 2,520,548
Amounts reclassified from accumulated other comprehensive loss	$ (435)	$ (375)	(918)	1,095
Net current-period other comprehensive income (loss)	396	376	(56)	(1,058)
Balance	2,302,952	2,237,610	2,302,952	2,237,610
Net unrealized gain (loss) on derivative instruments qualifying as hedges
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(2,209)	(2,575)	(2,300)	(2,667)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive loss	92	91	183	183
Amounts reclassified to accumulated other comprehensive loss from a regulatory asset			0
Net current-period other comprehensive income (loss)	92	91	183	183
Balance	(2,117)	(2,484)	(2,117)	(2,484)
Postretirement liability adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(33,781)	(35,852)	(33,221)	(34,257)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive loss	312	248	669	(1,347)
Amounts reclassified to accumulated other comprehensive loss from a regulatory asset			(917)
Net current-period other comprehensive income (loss)	312	248	(248)	(1,347)
Balance	(33,469)	(35,604)	(33,469)	(35,604)
Foreign currency translation adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(140)	(175)	(149)	(200)
Other comprehensive income (loss) before reclassifications	(15)	31	(6)	56
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Amounts reclassified to accumulated other comprehensive loss from a regulatory asset			0
Net current-period other comprehensive income (loss)	(15)	31	(6)	56
Balance	(155)	(144)	(155)	(144)
Net unrealized gain (loss) on available-for-sale investments
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(55)	20	(63)	(24)
Other comprehensive income (loss) before reclassifications	(24)	(30)	(51)	(19)
Amounts reclassified from accumulated other comprehensive loss	31	36	66	69
Amounts reclassified to accumulated other comprehensive loss from a regulatory asset			0
Net current-period other comprehensive income (loss)	7	6	15	50
Balance	(48)	26	(48)	26
Total accumulated other comprehensive loss
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(36,185)	(38,582)	(35,733)	(37,148)
Other comprehensive income (loss) before reclassifications	(39)	1	(57)	37
Amounts reclassified from accumulated other comprehensive loss	435	375	918	(1,095)
Amounts reclassified to accumulated other comprehensive loss from a regulatory asset			(917)
Net current-period other comprehensive income (loss)	396	376	(56)	(1,058)
Balance	$ (35,789)	$ (38,206)	$ (35,789)	$ (38,206)

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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Interest expense	$ (20,766)	$ (22,219)	$ (41,068)	$ (45,087)
Income taxes	(15,290)	(21,320)	(27,478)	(29,620)
Other income	782	872	1,798	1,921
Net income (loss)	41,215	(229,804)	78,539	(215,974)
Reclassification from accumulated other comprehensive income, current period, net of tax	(435)	(375)	(918)	1,095
Reclassification adjustment for loss on derivative instruments included in net income (loss)
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Reclassification from accumulated other comprehensive income, current period, net of tax	92	91	183	183
Reclassification adjustment for loss on derivative instruments included in net income (loss) | Reclassification out of accumulated other comprehensive income [Member] | Interest rate contract [Member]
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Interest expense	(148)	(147)	(295)	(297)
Income taxes	56	56	112	114
Net income (loss)	(92)	(91)	(183)	(183)
Amortization of postretirement liability gains (losses) included in net periodic benefit cost (credit)
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Reclassification from accumulated other comprehensive income, current period, net of tax	312	248	669	(1,347)
Amortization of postretirement liability gains (losses) included in net periodic benefit cost (credit) | Reclassification out of accumulated other comprehensive income [Member]
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Income taxes	190	150	406	(819)
Net periodic benefit cost (credit)	(502)	(398)	(1,075)	2,166
Net income (loss)	(312)	(248)	(669)	1,347
Reclassification adjustment for loss on available-for-sale investments included in net income (loss)
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Reclassification from accumulated other comprehensive income, current period, net of tax	31	36	66	69
Reclassification adjustment for loss on available-for-sale investments included in net income (loss) | Reclassification out of accumulated other comprehensive income [Member]
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Income taxes	17	19	36	37
Other income	(48)	(55)	(102)	(106)
Net income (loss)	$ (31)	$ (36)	$ (66)	$ (69)

Pronghorn (Details)

Pronghorn (Details) - Pronghorn [Member] - Disposal Group, Held-for-sale, Not Discontinued Operations [Member] - USD ($) $ in Millions	Jan. 01, 2017	Nov. 21, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percent of ownership to sell		50.00%
Proceeds	$ 100

Major classes of assets and lia

Major classes of assets and liabilities (Details 2) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Current assets:
Total current assets held for sale	$ 328	$ 14,391	$ 37,625
Noncurrent assets:
Total noncurrent assets held for sale	$ 76,183	196,664	$ 167,100
Pronghorn [Member] | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
Current assets:
Prepayments and other current assets		68
Total current assets held for sale		68
Noncurrent assets:
Net property, plant and equipment		93,424
Goodwill		9,737
Less allowance for impairment of assets held for sale		2,311
Total noncurrent assets held for sale		100,850
Total assets held for sale		$ 100,918

Noncontrolling interest (Detail

Noncontrolling interest (Details 3) - USD ($) $ in Millions	Mar. 31, 2017	Jun. 27, 2016	Feb. 07, 2013
Dakota Prairie Refining, LLC [Member] | WBI Energy [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Previous percentage of ownership			50.00%
Percentage of ownership acquired		50.00%
Dakota Prairie Refining, LLC [Member] | Calumet [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Previous percentage of ownership			50.00%
Refining [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Reversal of a liability accrual	$ 7
Reversal of a liability accrual, net of tax	$ 4.3

Major classes of assets and l51

Major classes of assets and liabilities held for sale (Details 4) - USD ($) $ in Thousands		Jun. 30, 2017		Dec. 31, 2016		Jun. 30, 2016
Current assets:
Total current assets held for sale		$ 328		$ 14,391		$ 37,625
Noncurrent assets:
Total noncurrent assets held for sale		76,183		196,664		167,100
Current liabilities:
Total current liabilities held for sale		4,481		9,924		28,237
Exploration and production [Member] | Discontinued operations, held-for-sale or disposed of by sale [Member]
Current assets:
Receivables, net		328		355		8,207
Income taxes receivable		0		0		5,348
Prepayments and other current assets		0		0		4
Total current assets held for sale		328		355		13,559
Noncurrent assets:
Net property, plant and equipment		2,064		5,507		5,507
Deferred income taxes		74,013		91,098		104,726
Other		161		161		161
Less allowance for impairment of assets held for sale		0		938		938
Total noncurrent assets held for sale		76,238		95,828		109,456
Total assets held for sale		76,566		96,183		123,015
Current liabilities:
Accounts payable		138		141		456
Taxes payable		7,171		19	[1]	0
Accrued compensation		0		0		1,459
Other accrued liabilities		2,724		2,358		10,849
Total current liabilities held for sale		10,033		2,518		12,764
Deferred credits and other liabilities:
Total liabilities held for sale		10,033		2,518		12,764
Refining [Member] | Discontinued operations, held-for-sale or disposed of by sale [Member]
Current assets:
Receivables, net		0		0		433
Income taxes receivable		5,552	[2]	13,987		12,550
Prepayments and other current assets		0		0		11,083
Total current assets held for sale		5,552		13,987		24,066
Noncurrent assets:
Deferred income taxes		0		0		57,644
Total noncurrent assets held for sale		0		0		57,644
Total assets held for sale		5,552		13,987		81,710
Current liabilities:
Accounts payable		0		7,425		7,170
Other accrued liabilities		0		0		8,303
Total current liabilities held for sale		0		7,425		15,473
Deferred credits and other liabilities:
Deferred income taxes (b)	[3]	55		14		0
Total noncurrent liabilities held for sale		55		14		0
Total liabilities held for sale		$ 55		$ 7,439		$ 15,473
[1]	On the Company's Consolidated Balance Sheets, this amount was reclassified to prepayments and other current assets and is reflectedin current assets held for sale.
[2]	On the Company's Consolidated Balance Sheets, this amount was reclassified to income taxes payable and is reflected in current liabilities held for sale.
[3]	On the Company's Consolidated Balance Sheets, these amounts were reclassified to noncurrent deferred income tax assets and are reflected in noncurrent assets held for sale.

Assets held for sale and disc52

Assets held for sale and discontinued operations Accounting pronouncement reclassification (Details 5) - Restatement adjustment [Member] - Accounting Standards Update 2015-17 [Member] - Exploration and production [Member] - Discontinued operations, held-for-sale or disposed of by sale [Member] $ in Millions	Jun. 30, 2016USD ($)
Other current assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Reclass to deferred tax asset	$ 47.5
Other current liabilities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Reclass to deferred tax asset	$ (4.1)

Impairment fair value (Details

Impairment fair value (Details 6) - Discontinued operations, held-for-sale or disposed of by sale [Member] - USD ($)	3 Months Ended
	Jun. 30, 2016	Mar. 31, 2016
Exploration and production [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair value impairment	$ 900,000	$ (1,400,000)
Fair value impairment after tax	600,000	$ (900,000)
Refining [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair value impairment	251,900,000
Fair value impairment after tax	$ 156,700,000

Business exit costs (Details 7)

Business exit costs (Details 7) - Discontinued operations, held-for-sale or disposed of by sale [Member] - Exploration and production [Member] - USD ($)	3 Months Ended		6 Months Ended		24 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017
Transaction costs [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business exit costs		$ 300,000
Other restructuring [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business exit costs	$ 3,800,000		$ 0	$ 5,600,000	$ 10,500,000
Facility closing [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business exit costs	400,000			$ 900,000
Contract Termination [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business exit costs	$ 3,200,000

Reconciliation of income and ex

Reconciliation of income and expenses (Details 8) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss from discontinued operations	[1]	$ (3,190)	$ (276,102)	$ (1,504)	$ (294,138)
Loss from discontinued operations attributable to noncontrolling interest		0	(120,651)	0	(131,691)
Discontinued operations, held-for-sale or disposed of by sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues		130	74,756	235	122,732
Operating expenses		1,205	443,756	(5,372)	513,526
Operating income (loss)		(1,075)	(369,000)	5,607	(390,794)
Other income (expense)		3	183	(13)	387
Interest expense		239	832	239	1,753
Income (loss) from discontinued operations before income taxes		(1,311)	(369,649)	5,355	(392,160)
Income taxes		1,879	(93,547)	6,859	(98,022)
Loss from discontinued operations		(3,190)	(276,102)	(1,504)	(294,138)
Loss from discontinued operations attributable to noncontrolling interest		0	(120,651)	0	(131,691)
Loss from discontinued operations attributable to the Company		(3,190)	(155,451)	(1,504)	(162,447)
Discontinued operations, held-for-sale or disposed of by sale [Member] | Refining [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pretax income (loss) attributable to the Company		$ 0	$ (244,000)	$ 6,900	$ (253,900)
[1]	Includes eliminations for the presentation of income tax adjustments between continuing and discontinued operations.

Goodwill rollforward (Details)

Goodwill rollforward (Details) - USD ($) $ in Thousands	6 Months Ended			12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016		Dec. 31, 2016
Goodwill [Roll Forward]
Balance at beginning of period	$ 631,791	$ 635,204	[1]	$ 635,204	[1]
Goodwill acquired during the year	0	6,323		6,324
Held for sale				(9,737)
Balance at end of period	631,791	641,527	[1]	631,791
Natural gas distribution [Member]
Goodwill [Roll Forward]
Balance at beginning of period	345,736	345,736		345,736
Goodwill acquired during the year	0	0		0
Held for sale				0
Balance at end of period	345,736	345,736		345,736
Pipeline and midstream [Member]
Goodwill [Roll Forward]
Balance at beginning of period	0	9,737	[1]	9,737	[1]
Goodwill acquired during the year		0		0
Held for sale				(9,737)
Balance at end of period		9,737	[1]	0
Accumulated impairment which occurred in prior periods		12,300		12,300
Construction materials and contracting [Member]
Goodwill [Roll Forward]
Balance at beginning of period	176,290	176,290		176,290
Goodwill acquired during the year	0	0		0
Held for sale				0
Balance at end of period	176,290	176,290		176,290
Construction services [Member]
Goodwill [Roll Forward]
Balance at beginning of period	109,765	103,441		103,441
Goodwill acquired during the year	0	6,323		6,324
Held for sale				0
Balance at end of period	$ 109,765	$ 109,764		$ 109,765
[1]	Balance is presented net of accumulated impairment of $12.3 million at the pipeline and midstream segment, which occurred in prior periods.

Other intangible assets (Detail

Other intangible assets (Details 2) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 4,785,000	$ 7,160,000	$ 4,785,000	$ 7,160,000	$ 5,925,000
Amortization of intangible assets	600,000	600,000	1,200,000	1,300,000
Estimated amortization expense for amortizable intangible assets [Abstract]
2,017	2,200,000		2,200,000
2,018	1,200,000		1,200,000
2,019	1,000,000		1,000,000
2,020	500,000		500,000
2,021	200,000		200,000
Thereafter	800,000		800,000
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	15,745,000	17,145,000	15,745,000	17,145,000	17,145,000
Intangible assets, less accumulated amortization	13,302,000	13,108,000	13,302,000	13,108,000	13,917,000
Intangible assets, net (excluding goodwill)	2,443,000	4,037,000	2,443,000	4,037,000	3,228,000
Noncompete agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,430,000	2,430,000	2,430,000	2,430,000	2,430,000
Intangible assets, less accumulated amortization	1,732,000	1,585,000	1,732,000	1,585,000	1,658,000
Intangible assets, net (excluding goodwill)	698,000	845,000	698,000	845,000	772,000
Other intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	7,086,000	7,764,000	7,086,000	7,764,000	7,768,000
Intangible assets, less accumulated amortization	5,442,000	5,486,000	5,442,000	5,486,000	5,843,000
Intangible assets, net (excluding goodwill)	$ 1,644,000	$ 2,278,000	$ 1,644,000	$ 2,278,000	$ 1,925,000

Fair value measurements Insuran

Fair value measurements Insurance contracts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Investments used to satisfy nonqualified benefit plans obligations	$ 73.1	$ 71.4	$ 73.1	$ 71.4	$ 70.9
Net unrealized gain (loss) of investments used to satisfy obligations under nonqualified benefit plans	$ 2.1	$ 2.3	$ 5	$ 3.9

Available-for-sale securities (

Available-for-sale securities (Details 2) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Available-for-sale securities [Abstract]
Cost	$ 10,356	$ 10,546	$ 10,420
Gross unrealized gains	13	8	52
Gross unrealized losses	(86)	(105)	(12)
Fair value	10,283	10,449	10,460
Mortgage backed securities [Member]
Available-for-sale securities [Abstract]
Cost	9,743	10,546	10,420
Gross unrealized gains	13	8	52
Gross unrealized losses	(86)	(105)	(12)
Fair value	9,670	$ 10,449	$ 10,460
US Treasury securities [Member]
Available-for-sale securities [Abstract]
Cost	613
Gross unrealized gains	0
Gross unrealized losses	0
Fair value	$ 613

Fair value measurements (Detail

Fair value measurements (Details 3) - USD ($) $ in Thousands	Jun. 30, 2017		Dec. 31, 2016		Jun. 30, 2016
Concentration risks, percentage [Abstract]
Percentage in fixed-income and other investments	50.00%		52.00%		66.00%
Percentage investment in common stock of large-cap companies	23.00%		22.00%		17.00%
Percentage investment in common stock of mid-cap companies	13.00%		13.00%		9.00%
Percentage investment in common stock of small-cap companies	11.00%		10.00%		6.00%
Percentage Investment in target date investments	2.00%		1.00%		1.00%
Percentage investment in cash and cash equivalents	1.00%		2.00%		1.00%
Fair value, measurements, recurring [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 89,291		$ 82,972		$ 83,340
Fair value, measurements, recurring [Member] | Money market funds [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	5,882		1,602		1,525
Fair value, measurements, recurring [Member] | insurance contract [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	73,126	[1]	70,921	[2]	71,355	[3]
Fair value, measurements, recurring [Member] | Mortgage backed securities [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	9,670		10,449		10,460
Fair value, measurements, recurring [Member] | US Treasury securities [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	613
Fair value, measurements, recurring [Member] | Fair value, inputs, level 1 [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	0		0		0
Fair value, measurements, recurring [Member] | Fair value, inputs, level 1 [Member] | Money market funds [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	0		0		0
Fair value, measurements, recurring [Member] | Fair value, inputs, level 1 [Member] | insurance contract [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	0	[1]	0	[2]	0	[3]
Fair value, measurements, recurring [Member] | Fair value, inputs, level 1 [Member] | Mortgage backed securities [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	0		0		0
Fair value, measurements, recurring [Member] | Fair value, inputs, level 1 [Member] | US Treasury securities [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	0
Fair value, measurements, recurring [Member] | Fair value, inputs, level 2 [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	89,291		82,972		83,340
Fair value, measurements, recurring [Member] | Fair value, inputs, level 2 [Member] | Money market funds [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	5,882		1,602		1,525
Fair value, measurements, recurring [Member] | Fair value, inputs, level 2 [Member] | insurance contract [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	73,126	[1]	70,921	[2]	71,355	[3]
Fair value, measurements, recurring [Member] | Fair value, inputs, level 2 [Member] | Mortgage backed securities [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	9,670		10,449		10,460
Fair value, measurements, recurring [Member] | Fair value, inputs, level 2 [Member] | US Treasury securities [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	613
Fair value, measurements, recurring [Member] | Fair value, inputs, level 3 [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	0		0		0
Fair value, measurements, recurring [Member] | Fair value, inputs, level 3 [Member] | Money market funds [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	0		0		0
Fair value, measurements, recurring [Member] | Fair value, inputs, level 3 [Member] | insurance contract [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	0	[1]	0	[2]	0	[3]
Fair value, measurements, recurring [Member] | Fair value, inputs, level 3 [Member] | Mortgage backed securities [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	0		$ 0		$ 0
Fair value, measurements, recurring [Member] | Fair value, inputs, level 3 [Member] | US Treasury securities [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 0
[1]	The insurance contract invests approximately 50 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, 2 percent in target date investments and 1 percent in cash equivalents.
[2]	The insurance contract invests approximately 52 percent in fixed-income investments, 22 percent in common stock of large-cap companies, 13 percent in common stock of mid-cap companies, 10 percent in common stock of small-cap companies, 1 percent in target date investments and 2 percent in cash equivalents.
[3]	The insurance contract invests approximately 66 percent in fixed-income investments, 17 percent in common stock of large-cap companies, 9 percent in common stock of mid-cap companies, 6 percent in common stock of small-cap companies, 1 percent in target date investments and 1 percent in cash equivalents.

Fair value measurements (Deta61

Fair value measurements (Details 4) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Carrying amount [Member]
Fair value, balance sheet grouping [Line Items]
Long-term debt	$ 1,761,476	$ 1,790,159	$ 1,987,307
Fair value [Member]
Fair value, balance sheet grouping [Line Items]
Long-term debt, fair value	$ 1,864,884	$ 1,841,885	$ 2,134,708

Equity (Details)

Equity (Details) - USD ($)	Apr. 02, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Increase decrease in stockholders equity roll forward
Total stockholders' equity				$ 2,316,244,000
Balance				2,316,244,000	$ 2,520,548,000
Net income (loss)		$ 41,215,000	$ (229,804,000)	78,539,000	(215,974,000)
Other comprehensive income (loss)		396,000	376,000	(56,000)	(1,058,000)
Dividends declared on preferred stocks				(171,000)	(343,000)
Dividends declared on common stock				(75,192,000)	(73,239,000)
Stock-based compensation				1,629,000	2,015,000
Repurchase of common stock				(1,684,000)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings					(323,000)
Net tax deficit on stock-based compensation					(1,664,000)
Contribution from noncontrolling interest					7,648,000
Total stockholders' equity		2,302,952,000	2,237,610,000	2,302,952,000	2,237,610,000
Balance		$ 2,302,952,000	2,237,610,000	2,302,952,000	2,237,610,000
Redeemable Preferred Stock Classified as Long Term Debt	$ 300,000
Payments for Repurchase of Redeemable Preferred Stock				15,900,000
Total stockholders’ equity [Member]
Increase decrease in stockholders equity roll forward
Total stockholders' equity					2,396,505,000
Net income (loss) attributable to parent					(84,283,000)
Other comprehensive income (loss)					(1,058,000)
Dividends declared on preferred stocks					(343,000)
Dividends declared on common stock					(73,239,000)
Stock-based compensation					2,015,000
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings					(323,000)
Net tax deficit on stock-based compensation					(1,664,000)
Contribution from noncontrolling interest					0
Total stockholders' equity			2,237,610,000		2,237,610,000
Noncontrolling interest [Member]
Increase decrease in stockholders equity roll forward
Noncontrolling interest					124,043,000
Loss from discontinued operations attributable to noncontrolling interest					(131,691,000)
Other comprehensive income (loss)					0
Dividends declared on preferred stocks					0
Dividends declared on common stock					0
Stock-based compensation					0
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings					0
Net tax deficit on stock-based compensation					0
Contribution from noncontrolling interest					7,648,000
Noncontrolling interest			$ 0		$ 0
Common Stock [Member]
Increase decrease in stockholders equity roll forward
Redemption of preferred stock				(757,000)
Preferred Stock [Member]
Increase decrease in stockholders equity roll forward
Redemption of preferred stock				$ (15,600,000)

Cash flow information (Details

Cash flow information (Details 1) - USD ($)		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016
Interest, net of amount capitalized and AFUDC - borrowed of $418 and $548 in 2017 and 2016, respectively		$ 39,207,000	$ 44,860,000
Income taxes paid, net	[1]	32,388,000	29,891,000
Property, plant and equipment additions in accounts payable		10,449,000	18,449,000
Capitalized interest and AFUDC borrowed		418,000	548,000
Continuing and discontinued operations [Member]
Income taxes paid, net		$ (3,600,000)	$ (500,000)
[1]	Income taxes refunded, net of discontinued operations, were $(3.6) million and $(500,000) for the six months ended June 30, 2017 and 2016, respectively.

Business segment data (Details)

Business segment data (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Revenues		$ 1,067,639	$ 1,043,948	$ 2,005,565	$ 1,904,163
Intersegment operating revenues		0	0	0	0
Earnings on common stock before income (loss) from discontinued operations		43,805	46,127	79,272	77,821
Loss from discontinued operations, net of tax	[1]	(3,190)	(276,102)	(1,504)	(294,138)
Loss from discontinued operations attributable to noncontrolling interest		0	(120,651)	0	(131,691)
Earnings (loss) on common stock		40,615	(109,324)	77,768	(84,626)
Regulated operation [Member]
Segment Reporting Information [Line Items]
Revenues		225,485	206,052	659,100	591,918
Intersegment operating revenues		6,353	6,594	27,841	27,691
Earnings on common stock before income (loss) from discontinued operations		10,554	5,809	57,303	47,457
Nonregulated operation [Member]
Segment Reporting Information [Line Items]
Revenues		842,154	837,896	1,346,465	1,312,245
Intersegment operating revenues		2,284	1,879	4,153	4,211
Earnings on common stock before income (loss) from discontinued operations		31,158	40,318	17,703	30,364
Electric [Member] | Regulated operation [Member]
Segment Reporting Information [Line Items]
Revenues		74,574	73,832	162,799	156,755
Intersegment operating revenues		0	0	0	0
Earnings on common stock before income (loss) from discontinued operations		7,859	8,022	22,191	19,141
Natural gas distribution [Member] | Regulated operation [Member]
Segment Reporting Information [Line Items]
Revenues		131,592	112,770	474,111	412,165
Intersegment operating revenues		0	0	0	0
Earnings on common stock before income (loss) from discontinued operations		(2,797)	(7,777)	25,064	17,464
Pipeline and midstream [Member] | Regulated operation [Member]
Segment Reporting Information [Line Items]
Revenues		19,319	19,450	22,190	22,998
Intersegment operating revenues		6,353	6,594	27,841	27,691
Earnings on common stock before income (loss) from discontinued operations		5,492	5,564	10,048	10,852
Pipeline and midstream [Member] | Nonregulated operation [Member]
Segment Reporting Information [Line Items]
Revenues		4,520	10,268	8,163	18,966
Intersegment operating revenues		59	36	93	119
Earnings on common stock before income (loss) from discontinued operations		(238)	737	(865)	739
Construction materials and contracting [Member] | Nonregulated operation [Member]
Segment Reporting Information [Line Items]
Revenues		501,426	541,257	702,203	751,108
Intersegment operating revenues		172	97	258	215
Earnings on common stock before income (loss) from discontinued operations		21,168	33,696	1,255	19,225
Construction services [Member] | Nonregulated operation [Member]
Segment Reporting Information [Line Items]
Revenues		336,009	285,924	635,580	541,424
Intersegment operating revenues		295	77	301	539
Earnings on common stock before income (loss) from discontinued operations		12,391	6,990	19,753	12,964
Other [Member] | Nonregulated operation [Member]
Segment Reporting Information [Line Items]
Revenues		199	447	519	747
Intersegment operating revenues		1,758	1,669	3,501	3,338
Earnings on common stock before income (loss) from discontinued operations		(2,163)	(1,105)	(2,440)	(2,564)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment operating revenues		(8,637)	(8,473)	(31,994)	(31,902)
Earnings on common stock before income (loss) from discontinued operations	[1]	$ 2,093	$ 0	$ 4,266	$ 0
[1]	Includes eliminations for the presentation of income tax adjustments between continuing and discontinued operations.

Employee benefit plans (Details

Employee benefit plans (Details) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension benefits [Member]
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	$ 0	$ 0		$ 0	$ 0
Interest cost	4,089,000	4,220,000		8,103,000	8,610,000
Expected return on assets	(5,234,000)	(5,182,000)		(10,263,000)	(10,462,000)
Amortization of prior service credit	0	0		0	0
Amortization of net actuarial loss	1,385,000	1,514,000		3,178,000	3,107,000
Net periodic benefit cost (credit), including amount capitalized	240,000	552,000		1,018,000	1,255,000
Less amount capitalized	73,000	121,000		180,000	202,000
Net periodic benefit cost (credit)	167,000	431,000		838,000	1,053,000
Other postretirement benefits [Member]
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	306,000	374,000		753,000	824,000
Interest cost	825,000	895,000		1,633,000	1,844,000
Expected return on assets	(1,175,000)	(1,118,000)		(2,320,000)	(2,267,000)
Amortization of prior service credit	(343,000)	(343,000)		(686,000)	(686,000)
Amortization of net actuarial loss	100,000	299,000		436,000	747,000
Net periodic benefit cost (credit), including amount capitalized	(287,000)	107,000		(184,000)	462,000
Less amount capitalized	(114,000)	4,000		(153,000)	38,000
Net periodic benefit cost (credit)	(173,000)	103,000		(31,000)	424,000
Supplemental employee retirement plans [Member]
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Net periodic benefit cost (credit)	$ 1,100,000	$ 1,200,000		$ 2,300,000	$ (700,000)
Curtailment gain			$ 3,300,000

Regulatory matters (Details)

Regulatory matters (Details) - USD ($)

Jul. 31, 2017

Jul. 26, 2017

Jul. 21, 2017

Jun. 30, 2017

Jun. 16, 2017

May 31, 2017

May 30, 2017

Apr. 28, 2017

Apr. 06, 2017

Jan. 17, 2017

Dec. 21, 2016

Dec. 02, 2016

Nov. 21, 2016

Oct. 14, 2016

Aug. 12, 2016

Jun. 10, 2016

Mar. 25, 2016

Mar. 09, 2016

Feb. 10, 2016

Jan. 05, 2016

WYPSC [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 3,200,000

Percent above current rates requested

13.10%

Rate increase approved

$ 2,700,000

Percent above current rates approved

11.10%

IPUC [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 10,200,000

Percent above current rates requested

4.10%

Rate increase approved

$ 4,100,000

Percent above current rates approved

1.60%

Public utilities, requested rate increase (decrease), amended, amount

$ 9,400,000

Public utilities, approved return on equity, percentage

9.50%

MTPSC [Member]

Regulatory matters [Line Items]

Public utilities gas and electric tax tracking adjustment

$ 814,000

Public utilities gas tax tracking adjustment, approved

474,000

Public utilities electric tax tracking adjustment, approved

$ 88,000

$ 251,000

MNPUC-Gas Cost Tariff [Member]

Regulatory matters [Line Items]

Public utilities, gas utility infrastructure cost tariff, requested

$ 456,000

MTPSC-Phase 2 [Member]

Regulatory matters [Line Items]

Rate increase approved

$ 4,700,000

WUTC-Pipeline Replacement [Member]

Regulatory matters [Line Items]

Public utilities, replacement cost recovery mechanism

$ 1,600,000

Public utilities, replacement cost recovery mechanism, percentage

0.75%

NDPSC-ADP [Member]

Regulatory matters [Line Items]

Estimated project cost

$ 85,000,000

NDPSC [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 13,400,000

Percent above current rates requested

6.60%

Rate increase approved

$ 7,500,000

Percent above current rates approved

3.70%

Interim rate increase (decrease), amount

$ 11,700,000

$ 13,000,000

Interim rate increase (decrease), percent

5.80%

6.50%

NDPSC-Renewable Rider [Member]

Regulatory matters [Line Items]

Public utilities, approved return on equity, percentage

9.65%

NDPSC-Electric Rider [Member]

Regulatory matters [Line Items]

Public utilities, approved return on equity, percentage

9.45%

NDPSC-Riders [Member]

Regulatory matters [Line Items]

Public utilities, approved return on equity, percentage

9.45%

NDPSC-Riders [Member] | NDPSC-Renewable Rider [Member]

Regulatory matters [Line Items]

Interim rate increase (decrease), amount

$ 15,100,000

Return on equity, percentage

10.50%

NDPSC-Riders [Member] | NDPSC-Electric Rider [Member]

Regulatory matters [Line Items]

Interim rate increase (decrease), amount

$ 9,700,000

Return on equity, percentage

10.50%

NDPSC-Riders [Member] | NDPSC-Transmission Adjustment [Member]

Regulatory matters [Line Items]

Interim rate increase (decrease), amount

$ 6,800,000

Return on equity, percentage

10.50%

Subsequent Event [Member] | NDPSC-Natural Gas [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 5,900,000

Percent above current rates requested

5.40%

Interim rate increase (decrease), amount

$ 4,600,000

Interim rate increase (decrease), percent

4.20%

Subsequent Event [Member] | WUTC [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 5,900,000

Percent above current rates requested

2.70%

Subsequent Event [Member] | NDPSC [Member]

Regulatory matters [Line Items]

Public utilities refund from current rates, percentage

19.00%

Litigation (Details)

Litigation (Details) - USD ($) $ in Millions	Nov. 03, 2016	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Loss Contingencies [Line Items]
Potential liabilities related to litigation and environmental matters		$ 33.7	$ 31.8	$ 27.4
Litigation [Domain]
Loss Contingencies [Line Items]
Loss contingency, damages awarded, value	$ 44.8

Environmental matters (Details

Environmental matters (Details 2) - USD ($)	6 Months Ended
	Jun. 30, 2017	Jan. 06, 2017
Portland Harbor Site [Member]
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 [Member]
Site Contingency [Line Items]
Total estimated costs for site remediation	3,500,000
Incurred costs for site remediation	$ 320,000
Percent of ongoing costs paid	50.00%
Estimated proportional share of cleanup liability	50.00%
Environmental matters accrual for site remediation	$ 1,600,000
Bremerton, WA Manufactured Gas Plant Site [Member]
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	200,000
Environmental matters accrual of investigative costs	7,400,000
Bellingham, WA Manufactured Gas Plant Site [Member]
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	8,000,000
Minimum [Member] | Bremerton, WA Manufactured Gas Plant Site [Member]
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	340,000
Maximum [Member] | Bremerton, WA Manufactured Gas Plant Site [Member]
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	$ 6,400,000

Guarantees (Details 3)

Guarantees (Details 3)	Jun. 30, 2017USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 106,200,000
Fixed maximum amounts guaranteed by year 2017	6,600,000
Fixed maximum amounts guaranteed by year 2018	24,800,000
Fixed maximum amounts guaranteed by year 2019	20,200,000
Fixed maximum amounts guaranteed by year 2020	47,400,000
Fixed maximum amounts guaranteed by year 2021.	500,000
Fixed maximum amounts guaranteed, thereafter	2,700,000
No scheduled maturity date	4,000,000
Amount outstanding under guarantees that is reflected on balance sheet	0
Letters of credit	33,800,000
Letters of credit set to expire - 2017	33,100,000
Letters of credit set to expire - 2018	700,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	765,500,000
Financial guarantee [Member]
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 58,500,000

Commitment and contingencies va

Commitment and contingencies variable interest entities (Details 4) $ in Millions	Jun. 30, 2017USD ($)
Fuel contract [Member]
Variable Interest Entities [Line Items]
Variable interest entity, reporting entity involvement, maximum loss exposure, amount	$ 42.1