MDU Resources (MDU) 10-Q 7 Nov 16 2016 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2016	Oct. 31, 2016
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	Sep. 30, 2016
Document fiscal year focus	2,016
Document fiscal period focus	Q3
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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating revenues:
Electric, natural gas distribution and regulated pipeline and midstream	$ 192,079	$ 185,417	$ 783,997	$ 807,585
Nonregulated pipeline and midstream, construction materials and contracting, construction services and other	1,016,488	1,012,925	2,328,733	2,189,640
Total operating revenues	1,208,567	1,198,342	3,112,730	2,997,225
Operating expenses:
Fuel and purchased power	16,800	20,616	54,725	63,761
Purchased natural gas sold	34,321	37,574	242,795	305,313
Operation and maintenance:
Electric, natural gas distribution and regulated pipeline and midstream	77,662	68,344	229,364	207,144
Nonregulated pipeline and midstream, construction materials and contracting, construction services and other	842,878	859,843	2,008,122	1,919,455
Depreciation, depletion and amortization	54,094	51,746	163,226	154,669
Taxes, other than income	36,128	32,391	116,864	109,039
Total operating expenses	1,061,883	1,070,514	2,815,096	2,759,381
Operating income	146,684	127,828	297,634	237,844
Other income	1,741	3,300	3,662	5,673
Interest expense	22,278	22,417	67,365	68,872
Income before income taxes	126,147	108,711	233,931	174,645
Income taxes	37,761	34,825	67,381	54,157
Income from continuing operations	88,386	73,886	166,550	120,488
Loss from discontinued operations, net of tax (Note 10)	(5,400)	(223,112)	(299,538)	(816,517)
Net income (loss)	82,986	(149,226)	(132,988)	(696,029)
Loss from discontinued operations attributable to noncontrolling interest (Note 10)	0	(9,778)	(131,691)	(21,060)
Dividends declared on preferred stocks	171	171	514	514
Earnings (loss) on common stock	$ 82,815	$ (139,619)	$ (1,811)	$ (675,483)
Earnings (loss) per common share - basic:
Earnings before discontinued operations	$ 0.45	$ 0.38	$ 0.85	$ 0.62
Discontinued operations attributable to the Company, net of tax	(0.03)	(1.10)	(0.86)	(4.09)
Earnings (loss) per common share - basic	0.42	(0.72)	(0.01)	(3.47)
Earnings (loss) per common share - diluted:
Earnings before discontinued operations	0.45	0.38	0.85	0.62
Discontinued operations attributable to the Company, net of tax	(0.03)	(1.10)	(0.86)	(4.09)
Earnings (loss) per common share - diluted	0.42	(0.72)	(0.01)	(3.47)
Dividends declared per common share	$ 0.1875	$ 0.1825	$ 0.5625	$ 0.5475
Weighted average common shares outstanding - basic	195,304	195,151	195,298	194,814
Weighted average common shares outstanding - diluted	195,811	195,169	195,794	194,833

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net income (loss)	$ 82,986	$ (149,226)	$ (132,988)	$ (696,029)
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 $60 for the three months ended and $170 and $181 for the nine months ended in 2016 and 2015, respectively	92	100	275	299
Postretirement liability adjustment:
Amortization of postretirement liability (gains) losses included in net periodic benefit cost, net of tax of $143 and $233 for the three months ended and $(676) and $881 for the nine months ended in 2016 and 2015, respectively	236	382	(1,111)	1,341
Foreign currency translation adjustment:
Foreign currency translation adjustment recognized during the period, net of tax of $(2) and $(44) for the three months ended and $32 and $(107) for the nine months ended in 2016 and 2015, respectively	(4)	(73)	52	(176)
Reclassification adjustment for loss on foreign currency translation adjustment included in net income (loss), net of tax of $0 and $0 for the three months ended and $0 and $491 for the nine months ended in 2016 and 2015, respectively	0	0	0	802
Foreign currency translation adjustment	(4)	(73)	52	626
Net unrealized gain (loss) on available-for-sale investments:
Net unrealized loss on available-for-sale investments arising during the period, net of tax of $(23) and $(19) for the three months ended and $(35) and $(57) for the nine months ended in 2016 and 2015, respectively	(42)	(35)	(65)	(105)
Reclassification adjustment for loss on available-for-sale investments included in net income (loss), net of tax of $18 and $15 for the three months ended and $57 and $53 for the nine months ended in 2016 and 2015, respectively	33	28	106	98
Net unrealized gain (loss) on available-for-sale investments	(9)	(7)	41	(7)
Other comprehensive income (loss)	315	402	(743)	2,259
Comprehensive income (loss)	83,301	(148,824)	(133,731)	(693,770)
Loss from discontinued operations attributable to noncontrolling interest	0	(9,778)	(131,691)	(21,060)
Comprehensive income (loss) attributable to common stockholders	$ 83,301	$ (139,046)	$ (2,040)	$ (672,710)

Consolidated Statements of Com4

Consolidated Statements of Comprehensive Income - Parenthetical - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassification adjustment for (gain) loss on derivative instruments included in net income, tax	$ 56	$ 60	$ 170	$ 181
Amortization of postretirement liability losses included in net periodic benefit cost, tax	143	233	(676)	881
Foreign currency translation adjustments recognized during the period, tax	(2)	(44)	32	(107)
Reclassification adjustment for foreign currency translation (gain) loss included in net income, tax	0	0	0	491
Net unrealized gain (loss) on available-for-sale investments arising during the period, tax	(23)	(19)	(35)	(57)
Reclassification adjustment for loss (gain) on available-for-sale investments included in net income, tax	$ 18	$ 15	$ 57	$ 53

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Current assets:
Cash and cash equivalents		$ 59,868	$ 83,903	$ 88,630
Receivables, net		665,142	582,475	663,342
Inventories		245,790	240,551	245,987
Deferred income taxes		31,378	33,121	31,892
Prepayments and other current assets		49,081	29,528	55,860
Current assets held for sale		93,366	54,847	117,823
Total current assets		1,144,625	1,024,425	1,203,534
Investments		126,048	119,704	118,063
Property, plant and equipment		6,588,445	6,387,702	6,199,880
Less accumulated depreciation, depletion and amortization		2,583,566	2,489,322	2,443,830
Net property, plant and equipment		4,004,879	3,898,380	3,756,050
Deferred charges and other assets:
Goodwill	[1]	641,527	635,204	635,204
Other intangible assets, net		6,529	7,342	7,908
Other		360,537	351,603	346,163
Noncurrent assets held for sale		69,061	565,509	909,150
Total deferred charges and other assets		1,077,654	1,559,658	1,898,425
Total assets		6,353,206	6,602,167	6,976,072
Current liabilities:
Long-term debt due within one year		93,598	238,539	258,539
Accounts payable		281,373	286,061	271,767
Taxes payable		59,747	46,880	42,637
Dividends payable		36,791	36,784	35,807
Accrued compensation		58,604	45,192	59,218
Other accrued liabilities		191,904	167,322	157,116
Current liabilities held for sale		22,185	130,375	123,628
Total current liabilities		744,202	951,153	948,712
Long-term debt		1,808,350	1,557,624	1,942,234
Deferred credits and other liabilities:
Deferred income taxes		693,704	696,750	718,348
Other		821,889	812,342	755,790
Noncurrent liabilities held for sale		0	63,750	96,117
Total deferred credits and other liabilities		1,515,593	1,572,842	1,570,255
Commitments and contingencies
Equity:
Preferred stocks		15,000	15,000	15,000
Common stockholders' equity:
Authorized - 500,000,000 shares, $1.00 par value Shares issued - 195,843,297 at September 30, 2016, 195,804,665 at September 30, 2015 and December 31, 2015		195,843	195,805	195,805
Other paid-in capital		1,231,396	1,230,119	1,228,875
Retained earnings		884,339	996,355	980,421
Accumulated other comprehensive loss		(37,891)	(37,148)	(39,844)
Treasury stock at cost - 538,921 shares		(3,626)	(3,626)	(3,626)
Total common stockholders' equity		2,270,061	2,381,505	2,361,631
Total stockholders' equity		2,285,061	2,396,505	2,376,631
Noncontrolling interest		0	124,043	138,240
Total equity		2,285,061	2,520,548	2,514,871
Total liabilities and equity		$ 6,353,206	$ 6,602,167	$ 6,976,072
[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	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
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	195,804,665	195,804,665
Treasury shares	538,921	538,921	538,921

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Operating activities:
Net income (loss)	$ (132,988)	$ (696,029)
Loss from discontinued operations, net of tax	(299,538)	(816,517)
Income from continuing operations	166,550	120,488
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation, depletion and amortization	163,226	154,669
Deferred income taxes	(1,346)	(48)
Changes in current assets and liabilities, net of acquisitions:
Receivables	(75,308)	(76,447)
Inventories	(4,153)	(3,660)
Other current assets	(18,824)	34,493
Accounts payable	15,514	47,629
Other current liabilities	48,973	5,187
Other noncurrent changes	(25,284)	(4,478)
Net cash provided by continuing operations	269,348	277,833
Net cash provided by discontinued operations	7,127	125,738
Net cash provided by operating activities	276,475	403,571
Investing activities:
Capital expenditures	(303,873)	(397,005)
Net proceeds from sale or disposition of property and other	17,583	37,679
Investments	56	1,309
Net cash used in continuing operations	(286,234)	(358,017)
Net cash provided by (used in) discontinued operations	31,918	(185,999)
Net cash used in investing activities	(254,316)	(544,016)
Financing activities:
Issuance of long-term debt	341,777	327,475
Repayment of long-term debt	(236,433)	(143,333)
Proceeds from issuance of common stock	0	21,894
Dividends paid	(110,366)	(107,028)
Tax withholding on stock-based compensation	(323)	0
Net cash provided by (used in) continuing operations	(5,345)	99,008
Net cash provided by (used in) discontinued operations	(40,852)	69,780
Net cash provided by (used in) financing activities	(46,197)	168,788
Effect of exchange rate changes on cash and cash equivalents	3	(192)
Increase (decrease) in cash and cash equivalents	(24,035)	28,151
Cash and cash equivalents - beginning of year	83,903	60,479
Cash and cash equivalents - end of period	$ 59,868	$ 88,630

Basis of presentation

Basis of presentation	9 Months Ended
	Sep. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of presentation	Basis of presentation The accompanying consolidated interim financial statements were prepared in conformity with the basis of presentation reflected in the consolidated financial statements included in the Company's 2015 Annual Report, and the standards of accounting measurement set forth in the interim reporting guidance in the ASC and any amendments thereto adopted by the FASB. 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 2015 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 September 30, 2016 , up to the date of issuance of these consolidated interim financial statements. 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 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 marketed 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 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 10 .

Seasonality of operations

Seasonality of operations	9 Months Ended
	Sep. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Seasonality of operations	Seasonality of operations Some of the Company's operations are highly seasonal and revenues from, and certain expenses for, such operations may fluctuate significantly among quarterly periods. Accordingly, the interim results for particular businesses, and for the Company as a whole, may not be indicative of results for the full fiscal year.

Accounts receivable and allowan

Accounts receivable and allowance for doubtful accounts	9 Months Ended
	Sep. 30, 2016
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 $26.3 million , $29.3 million and $27.8 million at September 30, 2016 and 2015 , and December 31, 2015 , respectively. The allowance for doubtful accounts is determined through a review of past due balances and other specific account data. Account balances are written off when management determines the amounts to be uncollectible. The Company's allowance for doubtful accounts at September 30, 2016 and 2015 , and December 31, 2015 , was $10.2 million , $9.0 million and $9.8 million , respectively.

Inventories and natural gas in

Inventories and natural gas in storage	9 Months Ended
	Sep. 30, 2016
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 average cost, or cost using the last-in, first-out method. All other inventories are stated at the lower of average cost or market 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: September 30, 2016 September 30, 2015 December 31, 2015 (In thousands) Aggregates held for resale $ 119,078 $ 115,736 $ 115,854 Asphalt oil 23,480 33,581 36,498 Natural gas in storage (current) 35,625 28,222 21,023 Materials and supplies 18,584 19,404 16,997 Merchandise for resale 15,672 15,563 15,318 Other 33,351 33,481 34,861 Total $ 245,790 $ 245,987 $ 240,551 The remainder of natural gas in storage, which largely represents the cost of gas required to maintain pressure levels for normal operating purposes, is included in other assets and was $ 49.1 million , $ 49.3 million and $ 49.1 million at September 30, 2016 and 2015 , and December 31, 2015 , respectively.

Impairment of long-lived assets

Impairment of long-lived assets	9 Months Ended
	Sep. 30, 2016
Asset Impairment Charges [Abstract]
Impairment of long-lived assets	Impairment of long-lived assets During the second quarter of 2015, the Company recognized an impairment of coalbed natural gas gathering assets at the pipeline and midstream segment of $3.0 million , which is recorded in operation and maintenance expense on the Consolidated Statements of Income. The impairment is related to coalbed natural gas gathering assets located in Wyoming where there had been continued decline in natural gas development and production activity due to low natural gas prices. The coalbed natural gas gathering assets were written down to their estimated fair value that was determined using the income approach. The Company negotiated a purchase and sale agreement for the sale of certain non-strategic natural gas gathering assets at the pipeline and midstream segment and, as a result, recognized an impairment during the third quarter of 2015 of $14.1 million , largely related to these assets, which is recorded in operation and maintenance expense on the Consolidated Statements of Income. The natural gas gathering assets were written down to their estimated fair value that was determined using the market approach. For more information on these nonrecurring fair value measurements, see Note 13 . For information regarding impairments related to the Company's discontinued operations, see Note 10 .

Earnings (loss) per common shar

Earnings (loss) per common share	9 Months Ended
	Sep. 30, 2016
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 Nine Months Ended September 30, September 30, 2016 2015 2016 2015 (In thousands) Weighted average common shares outstanding - basic 195,304 195,151 195,298 194,814 Effect of dilutive performance share awards 507 18 496 19 Weighted average common shares outstanding - diluted 195,811 195,169 195,794 194,833 Shares excluded from the calculation of diluted earnings per share — — — —

Cash flow information

Cash flow information	9 Months Ended
	Sep. 30, 2016
Supplemental Cash Flow Information [Abstract]
Cash flow information	Cash flow information Cash expenditures for interest and income taxes were as follows: Nine Months Ended September 30, 2016 2015 (In thousands) Interest, net of amounts capitalized and AFUDC - borrowed of $842 and $6,989 in 2016 and 2015, respectively $ 66,281 $ 69,253 Income taxes paid, net $ 73,771 $ 39,543 Noncash investing transactions were as follows: September 30, 2016 2015 (In thousands) Property, plant and equipment additions in accounts payable $ 22,560 $ 15,348

New accounting standards

New accounting standards	9 Months Ended
	Sep. 30, 2016
New Accounting Pronouncement or Change in Accounting Principle, Retrospective Adjustments [Abstract]
New accounting standards	New accounting standards 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. This guidance was to be effective for the Company on January 1, 2017. In August 2015, the FASB issued guidance deferring the effective date of the revenue guidance one year 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. 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 modified approach will require additional disclosures. The Company is evaluating the effects the adoption of the new revenue guidance will have on its results of operations, financial position, cash flows and disclosures, as well as its method of adoption. Simplifying the Presentation of Debt Issuance Costs In April 2015, the FASB issued guidance on simplifying the presentation of debt issuance costs in the financial statements. This guidance requires entities to present debt issuance costs as a direct deduction to the related debt liability. The amortization of these costs will be reported as interest expense. The guidance was effective for the Company on January 1, 2016, and was to be applied retrospectively. Early adoption of this guidance was permitted, however the Company did not elect to do so. The guidance required a reclassification of the debt issuance costs 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 debt issuance costs of $100,000 and $100,000 from prepayments and other current assets and $5.2 million and $6.0 million from deferred charges and other assets - other to long-term debt on its Consolidated Balance Sheets at September 30, 2015 and December 31, 2015, respectively. Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or its Equivalent) In May 2015, the FASB issued guidance on fair value measurement and disclosure requirements removing the requirement to include investments in the fair value hierarchy for which fair value is measured using the net asset value per share practical expedient. The new guidance also removes the requirement to make certain disclosures for all investments that are eligible to be measured at net asset value using the practical expedient, and rather limits those disclosures to investments for which the practical expedient has been elected. This guidance was effective for the Company on January 1, 2016, with early adoption permitted. The application of this guidance affected the Company's disclosures; however, it did not impact the Company's results of operations, financial position or cash flows. 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. This guidance will be effective for the Company on January 1, 2017, and should be applied prospectively with early adoption permitted as of the beginning of an interim or annual reporting period. The Company is planning to adopt the guidance on January 1, 2017, and does not anticipate the guidance to have a material effect on its results of operations, financial position or cash flows. 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 will require all deferred tax assets and liabilities to be classified as noncurrent. These amendments will align GAAP with IFRS. This guidance will be effective for the Company on January 1, 2017, with early adoption permitted. Entities will have the option to apply the guidance prospectively, for all deferred tax assets and liabilities, or retrospectively. The Company is planning to adopt the guidance in the fourth quarter of 2016 and will be applying the retrospective method of adoption. The guidance requires a reclassification of current deferred income taxes to noncurrent deferred income taxes on the Consolidated Balance Sheets; however, it does not impact the Company's results of operations or cash flows. 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. Leases In February 2016, the FASB issued guidance regarding leases. The guidance requires lessees to recognize a liability to make lease payments and a right-of-use asset representing its right to use the underlying asset for the lease term on the statement of financial position for leases with terms of more than 12 months. This guidance also requires additional disclosures. 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. 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. 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 will affect the income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. This guidance will be effective for the Company on January 1, 2017, with early adoption permitted in any interim or annual period. An entity that elects early adoption must adopt all of the amendments in the same period. Certain amendments of this guidance are to be applied retrospectively and others prospectively. The Company is planning to adopt the guidance on January 1, 2017. The Company anticipates the guidance will have an impact to the Consolidated Statements of Income and the Consolidated Balance Sheets on a prospective basis with all taxes related to share-based payments recognized as income tax expense or benefit and no longer recognized in additional paid-in capital. The Company anticipates the guidance will not have a material impact on its cash flows. 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. 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 then 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.

Comprehensive income (loss)

Comprehensive income (loss)	9 Months Ended
	Sep. 30, 2016
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 September 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 $ (2,484 ) $ (35,604 ) $ (144 ) $ 26 $ (38,206 ) Other comprehensive loss before reclassifications — — (4 ) (42 ) (46 ) Amounts reclassified from accumulated other comprehensive loss 92 236 — 33 361 Net current-period other comprehensive income (loss) 92 236 (4 ) (9 ) 315 Balance at end of period $ (2,392 ) $ (35,368 ) $ (148 ) $ 17 $ (37,891 ) Three Months Ended September 30, 2015 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 $ (2,872 ) $ (37,259 ) $ (130 ) $ 15 $ (40,246 ) Other comprehensive loss before reclassifications — — (73 ) (35 ) (108 ) Amounts reclassified from accumulated other comprehensive loss 100 382 — 28 510 Net current-period other comprehensive income (loss) 100 382 (73 ) (7 ) 402 Balance at end of period $ (2,772 ) $ (36,877 ) $ (203 ) $ 8 $ (39,844 ) Nine Months Ended September 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 — — 52 (65 ) (13 ) Amounts reclassified from accumulated other comprehensive loss 275 (1,111 ) — 106 (730 ) Net current-period other comprehensive income (loss) 275 (1,111 ) 52 41 (743 ) Balance at end of period $ (2,392 ) $ (35,368 ) $ (148 ) $ 17 $ (37,891 ) Nine Months Ended September 30, 2015 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 $ (3,071 ) $ (38,218 ) $ (829 ) $ 15 $ (42,103 ) Other comprehensive loss before reclassifications — — (176 ) (105 ) (281 ) Amounts reclassified from accumulated other comprehensive loss 299 1,341 802 98 2,540 Net current-period other comprehensive income (loss) 299 1,341 626 (7 ) 2,259 Balance at end of period $ (2,772 ) $ (36,877 ) $ (203 ) $ 8 $ (39,844 ) Reclassifications out of accumulated other comprehensive loss were as follows: Three Months Ended Nine Months Ended Location on Consolidated Statements of Income September 30, September 30, 2016 2015 2016 2015 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income (loss): Interest rate derivative instruments $ (148 ) $ (160 ) $ (445 ) $ (480 ) Interest expense 56 60 170 181 Income taxes (92 ) (100 ) (275 ) (299 ) Amortization of postretirement liability gains (losses) included in net periodic benefit cost (379 ) (615 ) 1,787 (2,222 ) (a) 143 233 (676 ) 881 Income taxes (236 ) (382 ) 1,111 (1,341 ) Reclassification adjustment for loss on foreign currency translation adjustment included in net income (loss) — — — (1,293 ) Other income — — — 491 Income taxes — — — (802 ) Reclassification adjustment for loss on available-for-sale investments included in net income (loss) (51 ) (43 ) (163 ) (151 ) Other income 18 15 57 53 Income taxes (33 ) (28 ) (106 ) (98 ) Total reclassifications $ (361 ) $ (510 ) $ 730 $ (2,540 ) (a) Included in net periodic benefit cost. For more information, see Note 17 .

Discontinued operations

Discontinued operations	9 Months Ended
	Sep. 30, 2016
Discontinued Operations and Disposal Groups [Abstract]
Discontinued operations	Discontinued operations The assets and liabilities of the Company's discontinued operations have been classified as held for sale and the results of operations are shown in 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 has cash in an escrow account for RINs obligations, which is included in current assets held for sale on the Consolidated Balance Sheet at September 30, 2016. The Company retained certain liabilities of Dakota Prairie Refining which are reflected in current liabilities held for sale on the Consolidated Balance Sheet at September 30, 2016. In October 2016, the RINs liability was paid and the cash was removed from escrow. Also, 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 19 . 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: September 30, 2016 September 30, 2015 December 31, 2015 (In thousands) Assets Current assets: Cash and cash equivalents $ — $ 564 $ 688 Receivables, net 13 14,648 7,693 Inventories — 12,354 13,176 Deferred income taxes — 116 (a) — Income taxes receivable 32,388 — 2,495 Prepayments and other current assets 7,741 7,125 6,214 Total current assets held for sale 40,142 34,807 30,266 Noncurrent assets: Net property, plant and equipment — 415,817 412,717 Deferred income taxes 2,984 — — Other — 5,052 9,627 Total noncurrent assets held for sale 2,984 420,869 422,344 Total assets held for sale $ 43,126 $ 455,676 $ 452,610 Liabilities Current liabilities: Short-term borrowings $ — $ 29,500 $ 45,500 Long-term debt due within one year — 4,125 5,250 Accounts payable 7,063 21,472 24,468 Taxes payable — 7,470 1,391 Deferred income taxes — — 272 Accrued compensation — 1,059 938 Other accrued liabilities 7,743 1,217 4,953 Total current liabilities held for sale 14,806 64,843 82,772 Noncurrent liabilities: Long-term debt — 64,875 63,750 Deferred income taxes — 11,632 (b) 23,569 (b) Total noncurrent liabilities held for sale — 76,507 87,319 Total liabilities held for sale $ 14,806 $ 141,350 $ 170,091 (a) On the Company's Consolidated Balance Sheet, this amount was reclassified to a current deferred income tax liability 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 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. At September 30, 2016, Dakota Prairie Refining had not incurred any material exit and disposal costs, and does not expect to incur any material exit and disposal costs. 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 marketed 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: September 30, 2016 September 30, 2015 December 31, 2015 (In thousands) Assets Current assets: Receivables, net $ 7,930 $ 24,703 $ 13,387 Inventories — 7,034 1,308 Commodity derivative instruments — 8,633 — Income taxes receivable 45,294 — 9,665 Prepayments and other current assets — 42,762 221 Total current assets held for sale 53,224 83,132 24,581 Noncurrent assets: Investments — 37 37 Net property, plant and equipment 5,507 1,114,285 793,422 Deferred income taxes 61,347 141,556 127,655 Other 161 162 161 Less allowance for impairment of assets held for sale 938 756,127 754,541 Total noncurrent assets held for sale 66,077 499,913 166,734 Total assets held for sale $ 119,301 $ 583,045 $ 191,315 Liabilities Current liabilities: Accounts payable $ 175 $ 32,375 $ 25,013 Taxes payable — 3,769 1,052 Deferred income taxes 4,120 4,955 3,620 Accrued compensation — 5,982 13,080 Other accrued liabilities 3,084 11,820 4,838 Total current liabilities held for sale 7,379 58,901 47,603 Noncurrent liabilities: Other — 31,242 — Total noncurrent liabilities held for sale — 31,242 — Total liabilities held for sale $ 7,379 $ 90,143 $ 47,603 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 Company recorded fair value impairments of $356.1 million ( $224.4 million after tax) and $756.1 million ( $476.4 million after tax) for the three and nine months ended September 30, 2015, respectively, related to the assets and liabilities classified as held for sale. The impairments 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. For more information related to the 2015 fair value impairments, see Part II, Item 8 - Note 2, in the 2015 Annual Report. The Company incurred transaction costs of approximately $300,000 in the first quarter of 2016, and $2.5 million in 2015. 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 $5.6 million of exit and disposal costs for the nine months ended September 30, 2016, and has incurred $10.5 million of exit and disposal costs to date. Fidelity incurred no exit and disposal costs for the three months ended September 30, 2016, 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. The Company incurred lease payments of approximately $900,000 in 2016. Lease termination payments of $3.2 million and $3.3 million were made during the second quarter of 2016 and fourth quarter of 2015, respectively. Existing office furniture and fixtures were relinquished to the lessor in the second quarter of 2016. Historically, the Company used the full-cost method of accounting for its oil and natural gas production activities. Under this method, all costs incurred in the acquisition, exploration and development of oil and natural gas properties are capitalized and amortized on the units-of-production method based on total proved reserves. Prior to the oil and natural gas properties being classified as held for sale, capitalized costs were subject to a "ceiling test" that limits such costs to the aggregate of the present value of future net cash flows from proved reserves discounted at 10 percent, as mandated under the rules of the SEC, plus the cost of unproved properties not subject to amortization, plus the effects of cash flow hedges, less applicable income taxes. Proved reserves and associated future cash flows are determined based on SEC Defined Prices and exclude cash outflows associated with asset retirement obligations that have been accrued on the balance sheet. If capitalized costs, less accumulated amortization and related deferred income taxes, exceed the full-cost ceiling at the end of any quarter, a permanent noncash write-down is required to be charged to earnings in that quarter regardless of subsequent price changes. The Company's capitalized cost under the full-cost method of accounting exceeded the full-cost ceiling at March 31, 2015. SEC Defined Prices, adjusted for market differentials, were used to calculate the ceiling test. Accordingly, the Company was required to write down its oil and natural gas producing properties. The Company recorded a $500.4 million ( $315.3 million after tax) noncash write-down in operating expenses from discontinued operations in the first quarter of 2015. 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 net loss from discontinued operations on the Company's Consolidated Statements of Income was as follows: Three Months Ended Nine Months Ended September 30, September 30, 2016 2015 2016 2015 (In thousands) Operating revenues $ 162 $ 140,428 $ 122,894 $ 288,537 Operating expenses 230 478,798 513,756 1,565,579 Operating loss (68 ) (338,370 ) (390,862 ) (1,277,042 ) Other income 375 298 762 2,758 Interest expense — 703 1,753 1,221 Income (loss) from discontinued operations before income taxes 307 (338,775 ) (391,853 ) (1,275,505 ) Income taxes 5,707 (115,663 ) (92,315 ) (458,988 ) Loss from discontinued operations (5,400 ) (223,112 ) (299,538 ) (816,517 ) Loss from discontinued operations attributable to noncontrolling interest — (9,778 ) (131,691 ) (21,060 ) Loss from discontinued operations attributable to the Company $ (5,400 ) $ (213,334 ) $ (167,847 ) $ (795,457 ) The pretax income (loss) from discontinued operations attributable to the Company, related to the operations of and activity associated with Dakota Prairie Refining, were $935,000 and $(8.6) million for the three months ended and $(253.0) million and $(18.4) million for the nine months ended September 30, 2016 and 2015, respectively.

Goodwill and other intangible a

Goodwill and other intangible assets	9 Months Ended
	Sep. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and other intangible assets	Goodwill and other intangible assets The changes in the carrying amount of goodwill were as follows: Nine Months Ended September 30, 2016 Balance as of January 1, 2016 * Goodwill Acquired Balance as of September 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. Nine Months Ended September 30, 2015 Balance as of January 1, 2015 * Goodwill Acquired During the Year Balance as of September 30, 2015 * (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 — 103,441 Total $ 635,204 $ — $ 635,204 * 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, 2015 Balance as of January 1, 2015 * Goodwill Acquired During the Year Balance as of December 31, 2015 * (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 — 103,441 Total $ 635,204 $ — $ 635,204 * 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: September 30, 2016 September 30, 2015 December 31, 2015 (In thousands) Customer relationships $ 17,145 $ 20,975 $ 20,975 Accumulated amortization (13,524 ) (16,455 ) (16,845 ) 3,621 4,520 4,130 Noncompete agreements 2,430 4,409 4,409 Accumulated amortization (1,622 ) (3,632 ) (3,655 ) 808 777 754 Other 7,764 8,300 8,304 Accumulated amortization (5,664 ) (5,689 ) (5,846 ) 2,100 2,611 2,458 Total $ 6,529 $ 7,908 $ 7,342 Amortization expense for amortizable intangible assets for the three and nine months ended September 30, 2016 , was $600,000 and $1.9 million , respectively. Amortization expense for amortizable intangible assets for the three and nine months ended September 30, 2015 , was $600,000 and $2.0 million , respectively. Estimated amortization expense for amortizable intangible assets is $2.5 million in 2016 , $2.2 million in 2017 , $1.2 million in 2018 , $1.0 million in 2019 , $500,000 in 2020 and $1.0 million thereafter.

Derivative instruments

Derivative instruments	9 Months Ended
	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative instruments	Derivative instruments The Company's policy allows the use of derivative instruments as part of an overall energy price, foreign currency and interest rate risk management program to efficiently manage and minimize commodity price, foreign currency and interest rate risk. As of September 30, 2016 , the Company had no outstanding commodity, foreign currency or interest rate hedges. The fair value of derivative instruments must be estimated as of the end of each reporting period and is recorded on the Consolidated Balance Sheets as an asset or a liability. Fidelity At September 30, 2015 , Fidelity held oil swap agreements with total forward notional volumes of 552,000 Bbl and natural gas swap agreements with total forward notional volumes of 920,000 MMBtu. At September 30, 2016 and December 31, 2015, Fidelity had no outstanding derivative agreements. Fidelity historically utilized these derivative instruments to manage a portion of the market risk associated with fluctuations in the price of oil and natural gas on its forecasted sales of oil and natural gas production. The realized and unrealized gains and losses on the commodity derivative instruments, which were not designated as hedges, were both included in loss from discontinued operations and the associated assets and liabilities were classified as held for sale. Centennial Centennial has historically entered into interest rate derivative instruments to manage a portion of its interest rate exposure on the forecasted issuance of long-term debt. As of September 30, 2016 and 2015 , and December 31, 2015 , Centennial had no outstanding interest rate swap agreements. Fidelity and Centennial The gains and losses on derivative instruments were as follows: Three Months Ended Nine Months Ended September 30, September 30, 2016 2015 2016 2015 (In thousands) Interest rate derivatives designated as cash flow hedges: Amount of loss reclassified from accumulated other comprehensive loss into interest expense (effective portion), net of tax $ 92 $ 100 $ 275 $ 299 Commodity derivatives not designated as hedging instruments: Amount of gain (loss) recognized in discontinued operations, before tax — 9,607 — (9,702 ) Over the next 12 months net losses of approximately $400,000 (after tax) are estimated to be reclassified from accumulated other comprehensive income (loss) into earnings, as the hedged transactions affect earnings. The location and fair value of the gross amount of the Company's derivative instruments on the Consolidated Balance Sheets were as follows: Asset Derivatives Location on Consolidated Balance Sheets Fair Value at September 30, 2015 (In thousands) Not designated as hedges: Commodity derivatives Current assets held for sale $ 8,633 Total asset derivatives $ 8,633 All of the Company's commodity derivative instruments at September 30, 2015 , were subject to legally enforceable master netting agreements. However, the Company's policy is to not offset fair value amounts for derivative instruments and, as a result, the Company's derivative instruments are presented gross on the Consolidated Balance Sheets. The gross derivative instruments (excluding settlement receivables and payables that may be subject to the same master netting agreements) presented on the Consolidated Balance Sheets and the amount eligible for offset under the master netting agreements are presented in the following table: September 30, 2015 Gross Amounts Recognized on the Consolidated Balance Sheets Gross Amounts Not Offset on the Consolidated Balance Sheets Net (In thousands) Assets: Commodity derivatives $ 8,633 $ — $ 8,633 Total assets $ 8,633 $ — $ 8,633

Fair value measurements

Fair value measurements	9 Months Ended
	Sep. 30, 2016
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 $72.8 million , $66.5 million and $67.5 million , at September 30, 2016 and 2015 , and December 31, 2015 , respectively, are classified as investments on the Consolidated Balance Sheets. The net unrealized gains on these investments were $1.4 million and $5.3 million for the three and nine months ended September 30, 2016 . The net unrealized loss on these investments was $1.7 million for the three months ended September 30, 2015, and the net unrealized gain on these investments was $700,000 for the nine months ended September 30, 2015 . 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: September 30, 2016 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 9,882 $ 43 $ (17 ) $ 9,908 Total $ 9,882 $ 43 $ (17 ) $ 9,908 September 30, 2015 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 7,843 $ 29 $ (18 ) $ 7,854 U.S. Treasury securities 2,324 4 (4 ) 2,324 Total $ 10,167 $ 33 $ (22 ) $ 10,178 December 31, 2015 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 9,128 $ 19 $ (49 ) $ 9,098 U.S. Treasury securities 1,315 — (6 ) 1,309 Total $ 10,443 $ 19 $ (55 ) $ 10,407 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 nine months ended September 30, 2016 and 2015 , there were no transfers between Levels 1 and 2. The Company's assets and liabilities measured at fair value on a recurring basis were as follows: Fair Value Measurements at September 30, 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 September 30, 2016 (In thousands) Assets: Money market funds $ — $ 2,284 $ — $ 2,284 Insurance contract* — 72,818 — 72,818 Available-for-sale securities: Mortgage-backed securities — 9,908 — 9,908 Total assets measured at fair value $ — $ 85,010 $ — $ 85,010 * The insurance contract invests approximately 65 percent in fixed-income investments, 18 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 September 30, 2015, Using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Balance at September 30, 2015 (In thousands) Assets: Money market funds $ — $ 1,219 $ — $ 1,219 Insurance contract* — 66,464 — 66,464 Available-for-sale securities: Mortgage-backed securities — 7,854 — 7,854 U.S. Treasury securities — 2,324 — 2,324 Total assets measured at fair value $ — $ 77,861 $ — $ 77,861 * The insurance contract invests approximately 65 percent in fixed-income investments, 18 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, 2015, 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, 2015 (In thousands) Assets: Money market funds $ — $ 1,420 $ — $ 1,420 Insurance contract* — 67,459 — 67,459 Available-for-sale securities: Mortgage-backed securities — 9,098 — 9,098 U.S. Treasury securities — 1,309 — 1,309 Total assets measured at fair value $ — $ 79,286 $ — $ 79,286 * The insurance contract invests approximately 63 percent in fixed-income investments, 19 percent in common stock of large-cap companies, 9 percent in common stock of mid-cap companies, 7 percent in common stock of small-cap companies, 1 percent in target date investments and 1 percent in cash equivalents. The Company applies the provisions of the fair value measurement standard to its nonrecurring, non-financial measurements, including long-lived asset impairments. These assets are not measured at fair value on an ongoing basis but are subject to fair value adjustments only in certain circumstances. The Company reviews the carrying value of its long-lived assets, excluding goodwill, whenever events or changes in circumstances indicate that such carrying amounts may not be recoverable. During the second quarter of 2015, coalbed natural gas gathering assets were reviewed for impairment and found to be impaired and were written down to their estimated fair value using the income approach. Under this approach, fair value is determined by using the present value of future estimated cash flows. The factors used to determine the estimated future cash flows include, but are not limited to, internal estimates of gathering revenue, future commodity prices and operating costs and equipment salvage values. The estimated cash flows are discounted using a rate that approximates the weighted average cost of capital of a market participant. These fair value inputs are not typically observable. At June 30, 2015, coalbed natural gas gathering assets were written down to the nonrecurring fair value measurement of $1.1 million . During the third quarter of 2015, the Company was negotiating the sale of certain non-strategic natural gas gathering assets at the pipeline and midstream segment and as a result these assets were found to be impaired and were written down to their estimated fair value using the market approach. The estimated fair value of natural gas gathering assets that were impaired at September 30, 2015, was largely determined by agreed upon pricing in a purchase and sale agreement that the Company was negotiating, and these assets were sold in the fourth quarter of 2015. At September 30, 2015, natural gas gathering assets were written down to the nonrecurring fair value measurement of $10.8 million . The fair value of these natural gas gathering assets have been categorized as Level 3 in the fair value hierarchy. The Company performed fair value assessments of the assets and liabilities classified as held for sale. For more information on these Level 3 nonrecurring fair value measurements, see Note 10 . 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 September 30, 2016 $ 1,901,948 $ 2,047,339 Long-term debt at September 30, 2015 $ 2,200,773 $ 2,277,074 Long-term debt at December 31, 2015 $ 1,796,163 $ 1,819,828 The carrying amounts of the Company's remaining financial instruments included in current assets and current liabilities approximate their fair values .

Long-term debt

Long-term debt	9 Months Ended
	Sep. 30, 2016
Debt Disclosure [Abstract]
Long-term debt [Text Block]	Long-term debt On September 23, 2016, Centennial amended its revolving credit agreement to decrease the borrowing limit by $150.0 million to $500.0 million and extend the termination date to September 23, 2021. The credit agreement contains customary covenants and provisions, including a covenant of Centennial not to permit, as of the end of any fiscal quarter, the ratio of total consolidated debt to total consolidated capitalization to be greater than 65 percent . Other covenants include restricted payments, restrictions on the sale of certain assets, limitations on subsidiary indebtedness and the making of certain loans and investments. Centennial's revolving credit agreement contains cross-default provisions. These provisions state that if Centennial or any subsidiary of Centennial fails to make any payment with respect to any indebtedness or contingent obligations, in excess of a specified amount, under any agreement that causes such indebtedness to be due prior to its stated maturity or the contingent obligation to become payable, the revolving credit agreement will be in default.

Equity

Equity	9 Months Ended
	Sep. 30, 2016
Equity [Abstract]
Equity	Equity A summary of the changes in equity was as follows: Nine Months Ended September 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 (1,297 ) (131,691 ) (132,988 ) Other comprehensive loss (743 ) — (743 ) Dividends declared on preferred stocks (514 ) — (514 ) Dividends declared on common stock (109,858 ) — (109,858 ) Stock-based compensation 2,955 — 2,955 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 September 30, 2016 $ 2,285,061 $ — $ 2,285,061 Nine Months Ended September 30, 2015 Total Stockholders' Equity Noncontrolling Interest Total Equity (In thousands) Balance at December 31, 2014 $ 3,134,041 $ 115,743 $ 3,249,784 Net loss (674,969 ) (21,060 ) (696,029 ) Other comprehensive income 2,259 — 2,259 Dividends declared on preferred stocks (514 ) — (514 ) Dividends declared on common stock (106,714 ) — (106,714 ) Stock-based compensation 2,266 — 2,266 Net tax deficit on stock-based compensation (1,632 ) — (1,632 ) Issuance of common stock 21,894 — 21,894 Contribution from noncontrolling interest — 52,000 52,000 Distribution to noncontrolling interest — (8,443 ) (8,443 ) Balance at September 30, 2015 $ 2,376,631 $ 138,240 $ 2,514,871

Business segment data

Business segment data	9 Months Ended
	Sep. 30, 2016
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, gathering and processing services, as well as oil gathering, through regulated and nonregulated pipeline systems and processing facilities primarily in the Rocky Mountain and northern Great Plains regions of the United States. 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 communications 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 and pollution liability 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 the Brazilian Transmission Lines. 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 marketed 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 10 . The information below follows the same accounting policies as described in Note 1 of the Company's Notes to Consolidated Financial Statements in the 2015 Annual Report. Information on the Company's businesses was as follows: Three Months Ended Nine Months Ended September 30, September 30, 2016 2015 2016 2015 (In thousands) External operating revenues: Regulated operations: Electric $ 82,156 $ 74,604 $ 238,911 $ 210,646 Natural gas distribution 87,941 89,520 500,106 553,058 Pipeline and midstream 21,982 21,293 44,980 43,881 192,079 185,417 783,997 807,585 Nonregulated operations: Pipeline and midstream 10,732 14,545 29,697 42,294 Construction materials and contracting 724,535 774,288 1,475,643 1,475,585 Construction services 280,801 223,676 822,226 670,594 Other 420 416 1,167 1,167 1,016,488 1,012,925 2,328,733 2,189,640 Total external operating revenues $ 1,208,567 $ 1,198,342 $ 3,112,730 $ 2,997,225 Intersegment operating revenues: Regulated operations: Electric $ — $ — $ — $ — Natural gas distribution — — — — Pipeline and midstream 3,278 3,740 30,969 31,365 3,278 3,740 30,969 31,365 Nonregulated operations: Pipeline and midstream 41 145 161 460 Construction materials and contracting 155 244 370 2,450 Construction services 3 2,112 541 17,298 Other 2,204 2,379 5,542 5,943 2,403 4,880 6,614 26,151 Intersegment eliminations (5,681 ) (8,620 ) (37,583 ) (57,516 ) Total intersegment operating revenues $ — $ — $ — $ — Three Months Ended Nine Months Ended September 30, September 30, 2016 2015 2016 2015 (In thousands) Earnings (loss) on common stock: Regulated operations: Electric $ 12,699 $ 12,605 $ 31,840 $ 26,842 Natural gas distribution (12,524 ) (12,298 ) 4,940 3,777 Pipeline and midstream 5,389 5,392 16,241 15,077 5,564 5,699 53,021 45,696 Nonregulated operations: Pipeline and midstream 1,304 (8,587 ) 2,043 (8,498 ) Construction materials and contracting 69,523 68,823 88,747 74,324 Construction services 7,234 4,742 20,198 16,505 Other (1,009 ) (2,203 ) (3,572 ) (11,560 ) 77,052 62,775 107,416 70,771 Intersegment eliminations* 5,599 5,241 5,599 3,507 Earnings on common stock before loss from discontinued operations 88,215 73,715 166,036 119,974 Loss from discontinued operations, net of tax* (5,400 ) (223,112 ) (299,538 ) (816,517 ) Loss from discontinued operations attributable to noncontrolling interest — (9,778 ) (131,691 ) (21,060 ) Total earnings (loss) on common stock $ 82,815 $ (139,619 ) $ (1,811 ) $ (675,483 ) * Includes eliminations for the presentation of income tax adjustments between continuing and discontinued operations.

Employee benefit plans

Employee benefit plans	9 Months Ended
	Sep. 30, 2016
Compensation and Retirement Disclosure [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 for the Company's pension and other postretirement benefit plans were as follows: Pension Benefits Other Postretirement Benefits Three Months Ended September 30, 2016 2015 2016 2015 (In thousands) Components of net periodic benefit cost: Service cost $ — $ — $ 412 $ 454 Interest cost 4,305 4,285 922 902 Expected return on assets (5,231 ) (5,563 ) (1,133 ) (1,199 ) Amortization of prior service credit — — (343 ) (343 ) Amortization of net actuarial loss 1,553 1,734 371 511 Net periodic benefit cost, including amount capitalized 627 456 229 325 Less amount capitalized 82 90 (34 ) 36 Net periodic benefit cost $ 545 $ 366 $ 263 $ 289 Pension Benefits Other Postretirement Benefits Nine Months Ended September 30, 2016 2015 2016 2015 (In thousands) Components of net periodic benefit cost: Service cost $ — $ 86 $ 1,236 $ 1,362 Interest cost 12,915 12,855 2,766 2,705 Expected return on assets (15,693 ) (16,689 ) (3,400 ) (3,597 ) Amortization of prior service cost (credit) — 36 (1,029 ) (1,028 ) Amortization of net actuarial loss 4,660 5,282 1,118 1,525 Curtailment loss — 258 — — Net periodic benefit cost, including amount capitalized 1,882 1,828 691 967 Less amount capitalized 284 219 4 98 Net periodic benefit cost $ 1,598 $ 1,609 $ 687 $ 869 Prior to 2013, defined pension plan benefits and accruals for all nonunion and certain union plans were frozen. On June 30, 2015, an additional union plan was frozen. As of June 30, 2015, all of the Company's defined pension plans were frozen. These employees were eligible to receive additional defined contribution plan benefits. 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 upgrades. Vesting for participants not fully vested was retained. The Company's net periodic benefit cost for these plans for the three and nine months ended September 30, 2016 , was $1.3 million and $600,000 , respectively, which reflects a curtailment gain of $3.3 million in the first quarter of 2016. The Company's net periodic benefit cost for these plans for the three and nine months ended September 30, 2015 , was $1.7 million and $5.3 million , respectively. Multiemployer plans On September 24, 2014, JTL - Wyoming provided notice to the Operating Engineers Local 800 & WY Contractors Association, Inc. Pension Plan for Wyoming that it was withdrawing from the plan effective October 26, 2014. The plan administrator will determine JTL - Wyoming's withdrawal liability. For the three months ended March 31, 2015, the Company accrued an additional withdrawal liability of approximately $2.4 million . The cumulative withdrawal liability is currently estimated at $16.4 million which has been accrued on the Consolidated Balance Sheets. The assessed withdrawal liability for this plan may be significantly different from the current estimate. Also, this plan's administrator has alleged that JTL - Wyoming owes additional contributions for periods of time prior to its withdrawal, which could affect its final assessed withdrawal liability. JTL - Wyoming disputes the plan administrator's demand for additional contributions, and on February 23, 2016, filed a declaratory judgment action in the United States District Court for the District of Wyoming to resolve the dispute. JTL - Wyoming is currently engaged in settlement discussions to resolve the declaratory judgment action.

Regulatory matters

Regulatory matters	9 Months Ended
	Sep. 30, 2016
Regulated Operations [Abstract]
Regulatory matters	Regulatory matters On June 30, 2015, Montana-Dakota filed an application with the SDPUC for an electric rate increase. Montana-Dakota requested a total increase of approximately $2.7 million annually or approximately 19.2 percent above current rates to recover Montana-Dakota’s investments in modifications to generation facilities to comply with new EPA requirements, the addition and/or replacement of capacity and energy requirements and transmission facilities along with the additional depreciation, operation and maintenance expenses and taxes associated with the increases in investment. An interim increase of $2.7 million , subject to refund, was implemented January 1, 2016. Montana-Dakota and the SDPUC staff filed a settlement stipulation reflecting an overall annual increase of approximately $1.4 million including a transmission cost recovery rider and an infrastructure rider. A settlement hearing was held on June 7, 2016. The SDPUC issued an order approving the settlement on June 15, 2016. The approved rates were effective with service rendered on and after July 1, 2016. The final approved rate increase was less than the interim rate increase implemented January 1, 2016; therefore, Montana-Dakota refunded the difference as bill credits on customer bills in October 2016. On June 30, 2015, Montana-Dakota filed an application for a natural gas rate increase with the SDPUC. Montana-Dakota requested a total increase of approximately $1.5 million annually or approximately 3.1 percent above current rates to recover increased operating expenses along with increased investment in facilities, including the related depreciation expense and taxes, partially offset by an increase in customers and throughput. An interim increase of $1.5 million , subject to refund, was implemented January 1, 2016. Montana-Dakota, the SDPUC staff and other interested parties filed a settlement stipulation reflecting an overall increase of approximately $1.2 million . A settlement hearing was held on June 7, 2016. The SDPUC issued an order approving the settlement on June 15, 2016. The approved rates were effective with service rendered on and after July 1, 2016. The final approved rate increase was less than the interim rate increase implemented January 1, 2016; therefore, Montana-Dakota refunded the difference as bill credits on customer bills in October 2016. On September 30, 2015, Great Plains filed an application for a natural gas rate increase with the MNPUC. Great Plains requested a total increase of approximately $1.6 million annually or approximately 6.4 percent above current rates to recover increased operating expenses along with increased investment in facilities, including the related depreciation expense and taxes. An interim increase of $1.5 million or approximately 6.4 percent, subject to refund, was effective with service rendered on and after January 1, 2016. A technical hearing was held April 7, 2016. The MNPUC issued an order on September 6, 2016, authorizing an increase of approximately $1.1 million annually or approximately 5.2 percent with the requirement that Great Plains submit a compliance filing within 30 days. On September 22, 2016, Great Plains submitted the required compliance filing which included a refund plan to return the amount of interim revenues collected above the final rates. The final rates will be implemented upon approval of the compliance filing by the MNPUC. 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. The interim rate is pending the determination of the return on equity in the general rate case application filed on October 14, 2016, as 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. 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 net investment authorized for the natural gas-fired internal combustion engines and the return on equity on both investments are pending in the general rate case application filed October 14, 2016, as 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 located 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. The interim rate is pending the determination of the return on equity in the general rate case application filed October 14, 2016, as discussed in this note. On December 1, 2015, Cascade filed an application with the WUTC for a natural gas rate increase. Cascade requested a total increase of approximately $10.5 million annually or approximately 4.2 percent above current rates. The requested increase includes rate recovery associated with increased infrastructure investment and the associated operating expenses. On July 7, 2016, the WUTC approved a settlement of $4.0 million annually. The approved rates were effective with service rendered on or after September 1, 2016. On April 29, 2016, Cascade filed an application with the OPUC for a natural gas rate increase of approximately $1.9 million annually or approximately 2.8 percent above current rates. The request includes rate recovery associated with pipeline replacement and improvement projects to ensure the integrity of Cascade's system. On October 6, 2016, Cascade, staff of the OPUC and the interveners in the case filed a stipulation and settlement agreement reflecting an annual increase of approximately $754,000 to be effective March 1, 2017. This matter is pending before the OPUC. On June 1, 2016, Cascade filed an application with the WUTC for an annual pipeline replacement cost recovery mechanism of $4.6 million annually or approximately 2.0 percent of additional revenue. The requested increase includes $2.4 million associated with incremental pipeline replacement investments and $2.2 million for an alternative recovery request of incremental operation and maintenance costs associated with a maximum allowable operating pressure validation plan. On October 17, 2016, Cascade filed an update to the application that reduced the incremental pipeline replacement investment to $1.9 million and removed the operation and maintenance costs associated with a maximum allowable operating pressure validation plan. On October 27, 2016, the WUTC allowed the pipeline replacement cost recovery mechanism to become effective November 1, 2016. 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. A hearing has been scheduled for January 18-19, 2017. This matter is pending before the WYPSC. 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. A hearing has been scheduled for March 1-2, 2017. This matter is pending before the IPUC. 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 , subject to refund, to be effective within 60 days of the filing. This matter is pending before the NDPSC.

Contingencies

Contingencies	9 Months Ended
	Sep. 30, 2016
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. 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. The Company had accrued liabilities of $20.0 million , $21.4 million and $19.5 million , which include liabilities held for sale, for contingencies, including litigation, production taxes, royalty claims and environmental matters at September 30, 2016 and 2015 , and December 31, 2015 , respectively, including amounts that may have been accrued for matters discussed in Litigation and Environmental matters within this note. Litigation Natural Gas Gathering Operations Omimex filed a complaint against WBI Energy Midstream in Montana Seventeenth Judicial District Court in July 2010 alleging WBI Energy Midstream breached a gathering contract with Omimex as a result of the increased operating pressures demanded by a third party on a natural gas gathering system in Montana. In December 2011, Omimex filed an amended complaint alleging WBI Energy Midstream breached obligations to operate its gathering system as a common carrier under United States and Montana law. WBI Energy Midstream removed the action to the United States District Court for the District of Montana. The parties subsequently settled the breach of contract claim and, subject to final determination on liability, stipulated to the damages on the common carrier claim, for amounts that are not material. A trial on the common carrier claim was held during July 2013. On December 9, 2014, the United States District Court for the District of Montana issued an order determining WBI Energy Midstream breached its obligations as a common carrier and ordered judgment in favor of Omimex for the amount of the stipulated damages. WBI Energy Midstream filed an appeal from the United States District Court for the District of Montana's order and judgment. The Company also is subject to other litigation, and actual and potential claims in the ordinary course of its business which may include, but are not limited to, matters involving property damage, personal injury, and environmental, contractual, statutory and regulatory obligations. Accruals are based on the best information available but actual losses in future periods are affected by various factors making them uncertain. After taking into account liabilities accrued for the foregoing matters, management believes that the outcomes with respect to the above issues and other probable and reasonably possible losses in excess of the amounts accrued, while uncertain, will not have a material effect upon the Company's financial position, results of operations or cash flows. 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 . Corrective action will not be taken until after the development of a proposed plan is complete, a ROD on the harbor site is issued and the remedial design/remedial action plans are approved by the EPA. On June 8, 2016, Region 10 of the EPA issued a Proposed Plan for the Portland Harbor Superfund Site that included a preferred cleanup alternative with an estimated cost of $746 million . Comments on the Proposed Plan were received through September 6, 2016. The EPA is expected to issue a ROD following review of the comments received on the Proposed Plan. 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. Several alternatives for cleanup have been identified, with preliminary cost estimates ranging from approximately $500,000 to $11.0 million . The Oregon DEQ released a ROD in January 2015 that selected a remediation alternative for the site as recommended in an earlier staff report. It is not known at this time what share of the cleanup costs will actually be borne by Cascade; however, Cascade anticipates its proportional share could be approximately 50 percent. Cascade has accrued $1.7 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. 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. Cascade has accrued $12.7 million for the remedial investigation, feasibility study and remediation of this site. 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 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 will 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 $64.9 million at September 30, 2016 , 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 September 30, 2016 , the fixed maximum amounts guaranteed under these agreements aggregated $110.0 million . The amounts of scheduled expiration of the maximum amounts guaranteed under these agreements aggregate $4.2 million in 2016 ; $30.3 million in 2017 ; $12.0 million in 2018 ; $59.5 million in 2019 ; and $4.0 million , which has no scheduled maturity date. There were no amounts outstanding under the above guarantees at September 30, 2016 . In the event of default under these guarantee obligations, the subsidiary issuing the guarantee for that particular obligation would be required to make payments under its guarantee. Certain subsidiaries have outstanding letters of credit to third parties related to insurance policies and other agreements, some of which are guaranteed by other subsidiaries of the Company. At September 30, 2016 , the fixed maximum amounts guaranteed under these letters of credit aggregated $34.9 million . The amounts of scheduled expiration of the maximum amounts guaranteed under these letters of credit aggregate $2.9 million in 2016 and $32.0 million in 2017. There were no amounts outstanding under the above letters of credit at September 30, 2016 . 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 September 30, 2016 . In the normal course of business, Centennial has surety bonds related to construction contracts and reclamation obligations of its subsidiaries. In the event a subsidiary of Centennial does not fulfill a bonded obligation, Centennial would be responsible to the surety bond company for completion of the bonded contract or obligation. A large portion of the surety bonds is expected to expire within the next 12 months; however, Centennial will likely continue to enter into surety bonds for its subsidiaries in the future. At September 30, 2016 , approximately $560.7 million of surety bonds were outstanding, which were not reflected on the Consolidated Balance Sheet. Variable interest entities The Company evaluates its arrangements and contracts with other entities to determine if they are VIEs and if so, if the Company is the primary beneficiary. Dakota Prairie Refining, LLC On February 7, 2013, WBI Energy and Calumet formed a limited liability company, Dakota Prairie Refining, and entered into an operating agreement to develop, build and operate Dakota Prairie Refinery in southwestern North Dakota. WBI Energy and Calumet each had a 50 percent ownership interest in Dakota Prairie Refining. WBI Energy's and Calumet's capital commitments, based on a total project cost of $300 million , under the agreement were $150 million and $75 million , respectively. Capital commitments for construction in excess of $300 million were shared equally between WBI Energy and Calumet. Dakota Prairie Refining entered into a term loan for project debt financing of $75 million on April 22, 2013. The operating agreement provided for allocation of profits and losses consistent with ownership interests; however, deductions attributable to project financing debt was allocated to Calumet. Calumet's cash distributions from Dakota Prairie Refining were decreased by the principal and interest paid on the project debt, while the cash distributions to WBI Energy were not decreased. Pursuant to the operating agreement, Centennial agreed to guarantee Dakota Prairie Refining's obligation under the term loan. The net loss attributable to noncontrolling interest on the Consolidated Statements of Income is pretax as Dakota Prairie Refining was a limited liability company. For more information related to the guarantee, see Guarantees in this note. Dakota Prairie Refining was determined to be a VIE, and the Company had determined that it was the primary beneficiary as it had an obligation to absorb losses that could be potentially significant to the VIE through WBI Energy's equity investment and Centennial's guarantee of the third-party term loan. Accordingly, the Company consolidated Dakota Prairie Refining in its financial statements and recorded a noncontrolling interest for Calumet's ownership interest. 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. 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. For more information on the Company's discontinued operations, see Note 10 . Dakota Prairie Refinery commenced operations in May 2015. The assets of Dakota Prairie Refining were used solely for the benefit of Dakota Prairie Refining. The total assets and liabilities of Dakota Prairie Refining were as follows: September 30, 2015 December 31, 2015 (In thousands) Assets Current assets: Cash and cash equivalents $ 625 $ 851 Accounts receivable 14,648 7,693 Inventories 12,354 13,176 Prepayments and other current assets 7,125 6,215 Total current assets 34,752 27,935 Net property, plant and equipment 428,383 425,123 Deferred charges and other assets: Other 5,052 9,626 Total deferred charges and other assets 5,052 9,626 Total assets $ 468,187 $ 462,684 Liabilities Current liabilities: Short-term borrowings $ 29,500 $ 45,500 Long-term debt due within one year 4,125 5,250 Accounts payable 21,686 24,766 Taxes payable 1,630 1,391 Accrued compensation 1,059 938 Other accrued liabilities 1,217 4,953 Total current liabilities 59,217 82,798 Long-term debt 64,875 63,750 Total liabilities $ 124,092 $ 146,548 Fuel Contract Coyote Station entered into a coal supply agreement with Coyote Creek that provides for the purchase of coal necessary to supply the coal requirements of the Coyote Station for the period May 2016 through December 2040. Coal purchased under the coal supply agreement is reflected in inventories on the Company's Consolidated Balance Sheets and is recovered from customers as a component of 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 September 30, 2016 , 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 $44.1 million .

Inventories and natural gas i27

Inventories and natural gas in storage (Tables)	9 Months Ended
	Sep. 30, 2016
Inventory Disclosure [Abstract]
Inventories	Inventories consisted of: September 30, 2016 September 30, 2015 December 31, 2015 (In thousands) Aggregates held for resale $ 119,078 $ 115,736 $ 115,854 Asphalt oil 23,480 33,581 36,498 Natural gas in storage (current) 35,625 28,222 21,023 Materials and supplies 18,584 19,404 16,997 Merchandise for resale 15,672 15,563 15,318 Other 33,351 33,481 34,861 Total $ 245,790 $ 245,987 $ 240,551

Earnings (loss) per common sh28

Earnings (loss) per common share (Tables)	9 Months Ended
	Sep. 30, 2016
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 Nine Months Ended September 30, September 30, 2016 2015 2016 2015 (In thousands) Weighted average common shares outstanding - basic 195,304 195,151 195,298 194,814 Effect of dilutive performance share awards 507 18 496 19 Weighted average common shares outstanding - diluted 195,811 195,169 195,794 194,833 Shares excluded from the calculation of diluted earnings per share — — — —

Cash flow information (Tables)

Cash flow information (Tables)	9 Months Ended
	Sep. 30, 2016
Supplemental Cash Flow Information [Abstract]
Supplemental cash flow information	Cash expenditures for interest and income taxes were as follows: Nine Months Ended September 30, 2016 2015 (In thousands) Interest, net of amounts capitalized and AFUDC - borrowed of $842 and $6,989 in 2016 and 2015, respectively $ 66,281 $ 69,253 Income taxes paid, net $ 73,771 $ 39,543 Noncash investing transactions were as follows: September 30, 2016 2015 (In thousands) Property, plant and equipment additions in accounts payable $ 22,560 $ 15,348

Comprehensive income (loss) (Ta

Comprehensive income (loss) (Tables)	9 Months Ended
	Sep. 30, 2016
Equity [Abstract]
Comprehensive income (loss)	The after-tax changes in the components of accumulated other comprehensive loss were as follows: Three Months Ended September 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 $ (2,484 ) $ (35,604 ) $ (144 ) $ 26 $ (38,206 ) Other comprehensive loss before reclassifications — — (4 ) (42 ) (46 ) Amounts reclassified from accumulated other comprehensive loss 92 236 — 33 361 Net current-period other comprehensive income (loss) 92 236 (4 ) (9 ) 315 Balance at end of period $ (2,392 ) $ (35,368 ) $ (148 ) $ 17 $ (37,891 ) Three Months Ended September 30, 2015 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 $ (2,872 ) $ (37,259 ) $ (130 ) $ 15 $ (40,246 ) Other comprehensive loss before reclassifications — — (73 ) (35 ) (108 ) Amounts reclassified from accumulated other comprehensive loss 100 382 — 28 510 Net current-period other comprehensive income (loss) 100 382 (73 ) (7 ) 402 Balance at end of period $ (2,772 ) $ (36,877 ) $ (203 ) $ 8 $ (39,844 ) Nine Months Ended September 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 — — 52 (65 ) (13 ) Amounts reclassified from accumulated other comprehensive loss 275 (1,111 ) — 106 (730 ) Net current-period other comprehensive income (loss) 275 (1,111 ) 52 41 (743 ) Balance at end of period $ (2,392 ) $ (35,368 ) $ (148 ) $ 17 $ (37,891 ) Nine Months Ended September 30, 2015 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 $ (3,071 ) $ (38,218 ) $ (829 ) $ 15 $ (42,103 ) Other comprehensive loss before reclassifications — — (176 ) (105 ) (281 ) Amounts reclassified from accumulated other comprehensive loss 299 1,341 802 98 2,540 Net current-period other comprehensive income (loss) 299 1,341 626 (7 ) 2,259 Balance at end of period $ (2,772 ) $ (36,877 ) $ (203 ) $ 8 $ (39,844 )
Reclassification out of accumulated other comprehensive income	Reclassifications out of accumulated other comprehensive loss were as follows: Three Months Ended Nine Months Ended Location on Consolidated Statements of Income September 30, September 30, 2016 2015 2016 2015 (In thousands) Reclassification adjustment for loss on derivative instruments included in net income (loss): Interest rate derivative instruments $ (148 ) $ (160 ) $ (445 ) $ (480 ) Interest expense 56 60 170 181 Income taxes (92 ) (100 ) (275 ) (299 ) Amortization of postretirement liability gains (losses) included in net periodic benefit cost (379 ) (615 ) 1,787 (2,222 ) (a) 143 233 (676 ) 881 Income taxes (236 ) (382 ) 1,111 (1,341 ) Reclassification adjustment for loss on foreign currency translation adjustment included in net income (loss) — — — (1,293 ) Other income — — — 491 Income taxes — — — (802 ) Reclassification adjustment for loss on available-for-sale investments included in net income (loss) (51 ) (43 ) (163 ) (151 ) Other income 18 15 57 53 Income taxes (33 ) (28 ) (106 ) (98 ) Total reclassifications $ (361 ) $ (510 ) $ 730 $ (2,540 ) (a) Included in net periodic benefit cost. For more information, see Note 17 .

Discontinued operations (Tables

Discontinued operations (Tables)	9 Months Ended
	Sep. 30, 2016
Discontinued Operations and Disposal Groups [Abstract]
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: September 30, 2016 September 30, 2015 December 31, 2015 (In thousands) Assets Current assets: Cash and cash equivalents $ — $ 564 $ 688 Receivables, net 13 14,648 7,693 Inventories — 12,354 13,176 Deferred income taxes — 116 (a) — Income taxes receivable 32,388 — 2,495 Prepayments and other current assets 7,741 7,125 6,214 Total current assets held for sale 40,142 34,807 30,266 Noncurrent assets: Net property, plant and equipment — 415,817 412,717 Deferred income taxes 2,984 — — Other — 5,052 9,627 Total noncurrent assets held for sale 2,984 420,869 422,344 Total assets held for sale $ 43,126 $ 455,676 $ 452,610 Liabilities Current liabilities: Short-term borrowings $ — $ 29,500 $ 45,500 Long-term debt due within one year — 4,125 5,250 Accounts payable 7,063 21,472 24,468 Taxes payable — 7,470 1,391 Deferred income taxes — — 272 Accrued compensation — 1,059 938 Other accrued liabilities 7,743 1,217 4,953 Total current liabilities held for sale 14,806 64,843 82,772 Noncurrent liabilities: Long-term debt — 64,875 63,750 Deferred income taxes — 11,632 (b) 23,569 (b) Total noncurrent liabilities held for sale — 76,507 87,319 Total liabilities held for sale $ 14,806 $ 141,350 $ 170,091 (a) On the Company's Consolidated Balance Sheet, this amount was reclassified to a current deferred income tax liability 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: September 30, 2016 September 30, 2015 December 31, 2015 (In thousands) Assets Current assets: Receivables, net $ 7,930 $ 24,703 $ 13,387 Inventories — 7,034 1,308 Commodity derivative instruments — 8,633 — Income taxes receivable 45,294 — 9,665 Prepayments and other current assets — 42,762 221 Total current assets held for sale 53,224 83,132 24,581 Noncurrent assets: Investments — 37 37 Net property, plant and equipment 5,507 1,114,285 793,422 Deferred income taxes 61,347 141,556 127,655 Other 161 162 161 Less allowance for impairment of assets held for sale 938 756,127 754,541 Total noncurrent assets held for sale 66,077 499,913 166,734 Total assets held for sale $ 119,301 $ 583,045 $ 191,315 Liabilities Current liabilities: Accounts payable $ 175 $ 32,375 $ 25,013 Taxes payable — 3,769 1,052 Deferred income taxes 4,120 4,955 3,620 Accrued compensation — 5,982 13,080 Other accrued liabilities 3,084 11,820 4,838 Total current liabilities held for sale 7,379 58,901 47,603 Noncurrent liabilities: Other — 31,242 — Total noncurrent liabilities held for sale — 31,242 — Total liabilities held for sale $ 7,379 $ 90,143 $ 47,603
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 net loss from discontinued operations on the Company's Consolidated Statements of Income was as follows: Three Months Ended Nine Months Ended September 30, September 30, 2016 2015 2016 2015 (In thousands) Operating revenues $ 162 $ 140,428 $ 122,894 $ 288,537 Operating expenses 230 478,798 513,756 1,565,579 Operating loss (68 ) (338,370 ) (390,862 ) (1,277,042 ) Other income 375 298 762 2,758 Interest expense — 703 1,753 1,221 Income (loss) from discontinued operations before income taxes 307 (338,775 ) (391,853 ) (1,275,505 ) Income taxes 5,707 (115,663 ) (92,315 ) (458,988 ) Loss from discontinued operations (5,400 ) (223,112 ) (299,538 ) (816,517 ) Loss from discontinued operations attributable to noncontrolling interest — (9,778 ) (131,691 ) (21,060 ) Loss from discontinued operations attributable to the Company $ (5,400 ) $ (213,334 ) $ (167,847 ) $ (795,457 )

Goodwill and other intangible32

Goodwill and other intangible assets (Tables)	9 Months Ended
	Sep. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the carrying amount of goodwill	The changes in the carrying amount of goodwill were as follows: Nine Months Ended September 30, 2016 Balance as of January 1, 2016 * Goodwill Acquired Balance as of September 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. Nine Months Ended September 30, 2015 Balance as of January 1, 2015 * Goodwill Acquired During the Year Balance as of September 30, 2015 * (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 — 103,441 Total $ 635,204 $ — $ 635,204 * 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, 2015 Balance as of January 1, 2015 * Goodwill Acquired During the Year Balance as of December 31, 2015 * (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 — 103,441 Total $ 635,204 $ — $ 635,204 * 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: September 30, 2016 September 30, 2015 December 31, 2015 (In thousands) Customer relationships $ 17,145 $ 20,975 $ 20,975 Accumulated amortization (13,524 ) (16,455 ) (16,845 ) 3,621 4,520 4,130 Noncompete agreements 2,430 4,409 4,409 Accumulated amortization (1,622 ) (3,632 ) (3,655 ) 808 777 754 Other 7,764 8,300 8,304 Accumulated amortization (5,664 ) (5,689 ) (5,846 ) 2,100 2,611 2,458 Total $ 6,529 $ 7,908 $ 7,342

Derivative instruments (Tables)

Derivative instruments (Tables)	9 Months Ended
	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of derivative instruments, gain (losses)	The gains and losses on derivative instruments were as follows: Three Months Ended Nine Months Ended September 30, September 30, 2016 2015 2016 2015 (In thousands) Interest rate derivatives designated as cash flow hedges: Amount of loss reclassified from accumulated other comprehensive loss into interest expense (effective portion), net of tax $ 92 $ 100 $ 275 $ 299 Commodity derivatives not designated as hedging instruments: Amount of gain (loss) recognized in discontinued operations, before tax — 9,607 — (9,702 )
Derivative instruments	The location and fair value of the gross amount of the Company's derivative instruments on the Consolidated Balance Sheets were as follows: Asset Derivatives Location on Consolidated Balance Sheets Fair Value at September 30, 2015 (In thousands) Not designated as hedges: Commodity derivatives Current assets held for sale $ 8,633 Total asset derivatives $ 8,633
Offsetting assets master netting	The gross derivative instruments (excluding settlement receivables and payables that may be subject to the same master netting agreements) presented on the Consolidated Balance Sheets and the amount eligible for offset under the master netting agreements are presented in the following table: September 30, 2015 Gross Amounts Recognized on the Consolidated Balance Sheets Gross Amounts Not Offset on the Consolidated Balance Sheets Net (In thousands) Assets: Commodity derivatives $ 8,633 $ — $ 8,633 Total assets $ 8,633 $ — $ 8,633

Fair value measurements (Tables

Fair value measurements (Tables)	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Available-for-sale securities	Details of available-for-sale securities were as follows: September 30, 2016 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 9,882 $ 43 $ (17 ) $ 9,908 Total $ 9,882 $ 43 $ (17 ) $ 9,908 September 30, 2015 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 7,843 $ 29 $ (18 ) $ 7,854 U.S. Treasury securities 2,324 4 (4 ) 2,324 Total $ 10,167 $ 33 $ (22 ) $ 10,178 December 31, 2015 Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Mortgage-backed securities $ 9,128 $ 19 $ (49 ) $ 9,098 U.S. Treasury securities 1,315 — (6 ) 1,309 Total $ 10,443 $ 19 $ (55 ) $ 10,407
Assets and liabilities measured at fair value on a recurring basis	The Company's assets and liabilities measured at fair value on a recurring basis were as follows: Fair Value Measurements at September 30, 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 September 30, 2016 (In thousands) Assets: Money market funds $ — $ 2,284 $ — $ 2,284 Insurance contract* — 72,818 — 72,818 Available-for-sale securities: Mortgage-backed securities — 9,908 — 9,908 Total assets measured at fair value $ — $ 85,010 $ — $ 85,010 * The insurance contract invests approximately 65 percent in fixed-income investments, 18 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 September 30, 2015, Using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Balance at September 30, 2015 (In thousands) Assets: Money market funds $ — $ 1,219 $ — $ 1,219 Insurance contract* — 66,464 — 66,464 Available-for-sale securities: Mortgage-backed securities — 7,854 — 7,854 U.S. Treasury securities — 2,324 — 2,324 Total assets measured at fair value $ — $ 77,861 $ — $ 77,861 * The insurance contract invests approximately 65 percent in fixed-income investments, 18 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, 2015, 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, 2015 (In thousands) Assets: Money market funds $ — $ 1,420 $ — $ 1,420 Insurance contract* — 67,459 — 67,459 Available-for-sale securities: Mortgage-backed securities — 9,098 — 9,098 U.S. Treasury securities — 1,309 — 1,309 Total assets measured at fair value $ — $ 79,286 $ — $ 79,286 * The insurance contract invests approximately 63 percent in fixed-income investments, 19 percent in common stock of large-cap companies, 9 percent in common stock of mid-cap companies, 7 percent in common stock of small-cap companies, 1 percent in target date investments and 1 percent in cash equivalents.
Fair value of long term debt outstanding	The estimated fair value of the Company's Level 2 long-term debt was as follows: Carrying Amount Fair Value (In thousands) Long-term debt at September 30, 2016 $ 1,901,948 $ 2,047,339 Long-term debt at September 30, 2015 $ 2,200,773 $ 2,277,074 Long-term debt at December 31, 2015 $ 1,796,163 $ 1,819,828

Equity (Tables)

Equity (Tables)	9 Months Ended
	Sep. 30, 2016
Equity [Abstract]
Summary of changes in equity	A summary of the changes in equity was as follows: Nine Months Ended September 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 (1,297 ) (131,691 ) (132,988 ) Other comprehensive loss (743 ) — (743 ) Dividends declared on preferred stocks (514 ) — (514 ) Dividends declared on common stock (109,858 ) — (109,858 ) Stock-based compensation 2,955 — 2,955 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 September 30, 2016 $ 2,285,061 $ — $ 2,285,061 Nine Months Ended September 30, 2015 Total Stockholders' Equity Noncontrolling Interest Total Equity (In thousands) Balance at December 31, 2014 $ 3,134,041 $ 115,743 $ 3,249,784 Net loss (674,969 ) (21,060 ) (696,029 ) Other comprehensive income 2,259 — 2,259 Dividends declared on preferred stocks (514 ) — (514 ) Dividends declared on common stock (106,714 ) — (106,714 ) Stock-based compensation 2,266 — 2,266 Net tax deficit on stock-based compensation (1,632 ) — (1,632 ) Issuance of common stock 21,894 — 21,894 Contribution from noncontrolling interest — 52,000 52,000 Distribution to noncontrolling interest — (8,443 ) (8,443 ) Balance at September 30, 2015 $ 2,376,631 $ 138,240 $ 2,514,871

Business segment data (Tables)

Business segment data (Tables)	9 Months Ended
	Sep. 30, 2016
Segment Reporting [Abstract]
Information on the Company's businesses	Information on the Company's businesses was as follows: Three Months Ended Nine Months Ended September 30, September 30, 2016 2015 2016 2015 (In thousands) External operating revenues: Regulated operations: Electric $ 82,156 $ 74,604 $ 238,911 $ 210,646 Natural gas distribution 87,941 89,520 500,106 553,058 Pipeline and midstream 21,982 21,293 44,980 43,881 192,079 185,417 783,997 807,585 Nonregulated operations: Pipeline and midstream 10,732 14,545 29,697 42,294 Construction materials and contracting 724,535 774,288 1,475,643 1,475,585 Construction services 280,801 223,676 822,226 670,594 Other 420 416 1,167 1,167 1,016,488 1,012,925 2,328,733 2,189,640 Total external operating revenues $ 1,208,567 $ 1,198,342 $ 3,112,730 $ 2,997,225 Intersegment operating revenues: Regulated operations: Electric $ — $ — $ — $ — Natural gas distribution — — — — Pipeline and midstream 3,278 3,740 30,969 31,365 3,278 3,740 30,969 31,365 Nonregulated operations: Pipeline and midstream 41 145 161 460 Construction materials and contracting 155 244 370 2,450 Construction services 3 2,112 541 17,298 Other 2,204 2,379 5,542 5,943 2,403 4,880 6,614 26,151 Intersegment eliminations (5,681 ) (8,620 ) (37,583 ) (57,516 ) Total intersegment operating revenues $ — $ — $ — $ — Three Months Ended Nine Months Ended September 30, September 30, 2016 2015 2016 2015 (In thousands) Earnings (loss) on common stock: Regulated operations: Electric $ 12,699 $ 12,605 $ 31,840 $ 26,842 Natural gas distribution (12,524 ) (12,298 ) 4,940 3,777 Pipeline and midstream 5,389 5,392 16,241 15,077 5,564 5,699 53,021 45,696 Nonregulated operations: Pipeline and midstream 1,304 (8,587 ) 2,043 (8,498 ) Construction materials and contracting 69,523 68,823 88,747 74,324 Construction services 7,234 4,742 20,198 16,505 Other (1,009 ) (2,203 ) (3,572 ) (11,560 ) 77,052 62,775 107,416 70,771 Intersegment eliminations* 5,599 5,241 5,599 3,507 Earnings on common stock before loss from discontinued operations 88,215 73,715 166,036 119,974 Loss from discontinued operations, net of tax* (5,400 ) (223,112 ) (299,538 ) (816,517 ) Loss from discontinued operations attributable to noncontrolling interest — (9,778 ) (131,691 ) (21,060 ) Total earnings (loss) on common stock $ 82,815 $ (139,619 ) $ (1,811 ) $ (675,483 ) * Includes eliminations for the presentation of income tax adjustments between continuing and discontinued operations.

Employee benefit plans (Tables)

Employee benefit plans (Tables)	9 Months Ended
	Sep. 30, 2016
Compensation and Retirement Disclosure [Abstract]
Schedule of net benefit costs	Components of net periodic benefit cost for the Company's pension and other postretirement benefit plans were as follows: Pension Benefits Other Postretirement Benefits Three Months Ended September 30, 2016 2015 2016 2015 (In thousands) Components of net periodic benefit cost: Service cost $ — $ — $ 412 $ 454 Interest cost 4,305 4,285 922 902 Expected return on assets (5,231 ) (5,563 ) (1,133 ) (1,199 ) Amortization of prior service credit — — (343 ) (343 ) Amortization of net actuarial loss 1,553 1,734 371 511 Net periodic benefit cost, including amount capitalized 627 456 229 325 Less amount capitalized 82 90 (34 ) 36 Net periodic benefit cost $ 545 $ 366 $ 263 $ 289 Pension Benefits Other Postretirement Benefits Nine Months Ended September 30, 2016 2015 2016 2015 (In thousands) Components of net periodic benefit cost: Service cost $ — $ 86 $ 1,236 $ 1,362 Interest cost 12,915 12,855 2,766 2,705 Expected return on assets (15,693 ) (16,689 ) (3,400 ) (3,597 ) Amortization of prior service cost (credit) — 36 (1,029 ) (1,028 ) Amortization of net actuarial loss 4,660 5,282 1,118 1,525 Curtailment loss — 258 — — Net periodic benefit cost, including amount capitalized 1,882 1,828 691 967 Less amount capitalized 284 219 4 98 Net periodic benefit cost $ 1,598 $ 1,609 $ 687 $ 869

Commitment and contingencies di

Commitment and contingencies disclosure (Tables)	9 Months Ended
	Sep. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Limited liability project reflected on consolidated balance sheet	The total assets and liabilities of Dakota Prairie Refining were as follows: September 30, 2015 December 31, 2015 (In thousands) Assets Current assets: Cash and cash equivalents $ 625 $ 851 Accounts receivable 14,648 7,693 Inventories 12,354 13,176 Prepayments and other current assets 7,125 6,215 Total current assets 34,752 27,935 Net property, plant and equipment 428,383 425,123 Deferred charges and other assets: Other 5,052 9,626 Total deferred charges and other assets 5,052 9,626 Total assets $ 468,187 $ 462,684 Liabilities Current liabilities: Short-term borrowings $ 29,500 $ 45,500 Long-term debt due within one year 4,125 5,250 Accounts payable 21,686 24,766 Taxes payable 1,630 1,391 Accrued compensation 1,059 938 Other accrued liabilities 1,217 4,953 Total current liabilities 59,217 82,798 Long-term debt 64,875 63,750 Total liabilities $ 124,092 $ 146,548

Basis of presentation (Details)

Basis of presentation (Details)	Jun. 27, 2016	Feb. 07, 2013
WBI Energy [Member]
Noncontrolling Interest [Line Items]
Previous percentage of ownership		50.00%
Percentage of ownership acquired	50.00%
Calumet [Member]
Noncontrolling Interest [Line Items]
Previous percentage of ownership		50.00%

Accounts receivable and allow40

Accounts receivable and allowance for doubtful accounts (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Receivables [Abstract]
Receivables past due 90 days or more	$ 26.3	$ 27.8	$ 29.3
Allowance for doubtful accounts receivable	$ 10.2	$ 9.8	$ 9

Inventories and natural gas i41

Inventories and natural gas in storage (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Inventory Disclosure [Abstract]
Aggregates held for resale	$ 119,078	$ 115,854	$ 115,736
Asphalt oil	23,480	36,498	33,581
Natural gas in storage (current)	35,625	21,023	28,222
Materials and supplies	18,584	16,997	19,404
Merchandise for resale	15,672	15,318	15,563
Other	33,351	34,861	33,481
Total	245,790	240,551	245,987
Natural gas in storage noncurrent	$ 49,100	$ 49,100	$ 49,300

Impairment of long-lived asse42

Impairment of long-lived assets (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2015	Jun. 30, 2015
Asset Impairment Charges [Abstract]
Asset impairment charges	$ 14.1	$ 3

Earnings (loss) per common sh43

Earnings (loss) per common share (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	195,304	195,151	195,298	194,814
Effect of dilutive performance share awards	507	18	496	19
Weighted average common shares outstanding - diluted	195,811	195,169	195,794	194,833
Shares excluded from the calculation of diluted earnings per share	0	0	0	0

Cash flow information (Details

Cash flow information (Details 1) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Supplemental Cash Flow Information [Abstract]
Interest, net of amounts capitalized and AFUDC - borrowed of $842 and $6,989 in 2016 and 2015, respectively	$ 66,281	$ 69,253
Capitalized interest and AFUDC borrowed	842	6,989
Income taxes paid, net	73,771	39,543
Property, plant and equipment additions in accounts payable	$ 22,560	$ 15,348

New accounting standards Debt I

New accounting standards Debt Issuance Costs (Details) - Accounting Standards Update 2015-03 [Member] - Restatement adjustment [Member] - USD ($)	Dec. 31, 2015	Sep. 30, 2015
Prepayments and other current assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclass of debt issuance costs, current	$ 100,000	$ 100,000
Other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclass of debt issuance costs, non-current	$ 6,000,000	$ 5,200,000

Comprehensive income (loss) (De

Comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated other comprehensive income (loss) [Roll Forward]
Balance			$ 2,520,548	$ 3,249,784
Amounts reclassified from accumulated other comprehensive loss	$ (361)	$ (510)	730	(2,540)
Net current-period other comprehensive income (loss)	315	402	(743)	2,259
Balance	2,285,061	2,514,871	2,285,061	2,514,871
Net unrealized gain (loss) on derivative instruments qualifying as hedges
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(2,484)	(2,872)	(2,667)	(3,071)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive loss	92	100	275	299
Net current-period other comprehensive income (loss)	92	100	275	299
Balance	(2,392)	(2,772)	(2,392)	(2,772)
Postretirement liability adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(35,604)	(37,259)	(34,257)	(38,218)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive loss	236	382	(1,111)	1,341
Net current-period other comprehensive income (loss)	236	382	(1,111)	1,341
Balance	(35,368)	(36,877)	(35,368)	(36,877)
Foreign currency translation adjustment
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(144)	(130)	(200)	(829)
Other comprehensive income (loss) before reclassifications	(4)	(73)	52	(176)
Amounts reclassified from accumulated other comprehensive loss	0	0	0	802
Net current-period other comprehensive income (loss)	(4)	(73)	52	626
Balance	(148)	(203)	(148)	(203)
Net unrealized gain (loss) on available-for-sale investments
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	26	15	(24)	15
Other comprehensive income (loss) before reclassifications	(42)	(35)	(65)	(105)
Amounts reclassified from accumulated other comprehensive loss	33	28	106	98
Net current-period other comprehensive income (loss)	(9)	(7)	41	(7)
Balance	17	8	17	8
Total accumulated other comprehensive loss
Accumulated other comprehensive income (loss) [Roll Forward]
Balance	(38,206)	(40,246)	(37,148)	(42,103)
Other comprehensive income (loss) before reclassifications	(46)	(108)	(13)	(281)
Amounts reclassified from accumulated other comprehensive loss	361	510	(730)	2,540
Net current-period other comprehensive income (loss)	315	402	(743)	2,259
Balance	$ (37,891)	$ (39,844)	$ (37,891)	$ (39,844)

Reclassification out of accumul

Reclassification out of accumulated other comprehensive income (loss) (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Interest expense	$ (22,278)	$ (22,417)	$ (67,365)	$ (68,872)
Income taxes	(37,761)	(34,825)	(67,381)	(54,157)
Other income	1,741	3,300	3,662	5,673
Net income (loss)	82,986	(149,226)	(132,988)	(696,029)
Reclassification from accumulated other comprehensive income, current period, net of tax	(361)	(510)	730	(2,540)
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	100	275	299
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)	(160)	(445)	(480)
Income taxes	56	60	170	181
Net income (loss)	(92)	(100)	(275)	(299)
Amortization of postretirement liability gains (losses) included in net periodic benefit cost
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Reclassification from accumulated other comprehensive income, current period, net of tax	236	382	(1,111)	1,341
Amortization of postretirement liability gains (losses) included in net periodic benefit cost | Reclassification out of accumulated other comprehensive income [Member]
Reclassification adjustment out of accumulated other comprehensive income [Line Items]
Income taxes	143	233	(676)	881
Net periodic benefit cost	(379)	(615)	1,787	(2,222)
Net income (loss)	(236)	(382)	1,111	(1,341)
Reclassification adjustment for loss on foreign currency translation adjustment 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	0	0	0	802
Reclassification adjustment for loss on foreign currency translation adjustment 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	0	0	0	491
Other income	0	0	0	(1,293)
Net income (loss)	0	0	0	(802)
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	33	28	106	98
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	18	15	57	53
Other income	(51)	(43)	(163)	(151)
Net income (loss)	$ (33)	$ (28)	$ (106)	$ (98)

Discontinued operations Noncont

Discontinued operations Noncontrolling interest (Details)	Jun. 27, 2016	Feb. 07, 2013
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%
Calumet [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Previous percentage of ownership		50.00%

Major classes of assets and lia

Major classes of assets and liabilities (Details 2) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015		Sep. 30, 2015
Current assets:
Total current assets held for sale	$ 93,366	$ 54,847		$ 117,823
Noncurrent assets:
Total noncurrent assets held for sale	69,061	565,509		909,150
Current liabilities:
Total current liabilities held for sale	22,185	130,375		123,628
Noncurrent liabilities:
Total noncurrent liabilities held for sale	0	63,750		96,117
Refining [Member] | Discontinued operations, held-for-sale or disposed of by sale [Member]
Current assets:
Cash and cash equivalents	0	688		564
Receivables, net	13	7,693		14,648
Inventories	0	13,176		12,354
Deferred income taxes	0	0		116	[1]
Income taxes receivable	32,388	2,495		0
Prepayments and other current assets	7,741	6,214		7,125
Total current assets held for sale	40,142	30,266		34,807
Noncurrent assets:
Net property, plant and equipment	0	412,717		415,817
Deferred income taxes	2,984	0		0
Other	0	9,627		5,052
Total noncurrent assets held for sale	2,984	422,344		420,869
Total assets held for sale	43,126	452,610		455,676
Current liabilities:
Short-term borrowings	0	45,500		29,500
Long-term debt due within one year	0	5,250		4,125
Accounts payable	7,063	24,468		21,472
Taxes payable	0	1,391		7,470
Deferred income taxes	0	272		0
Accrued compensation	0	938		1,059
Other accrued liabilities	7,743	4,953		1,217
Total current liabilities held for sale	14,806	82,772		64,843
Noncurrent liabilities:
Long-term debt	0	63,750		64,875
Deferred income taxes	0	23,569	[2]	11,632	[2]
Total noncurrent liabilities held for sale	0	87,319		76,507
Total liabilities held for sale	14,806	170,091		141,350
Exploration and production [Member] | Discontinued operations, held-for-sale or disposed of by sale [Member]
Current assets:
Receivables, net	7,930	13,387		24,703
Inventories	0	1,308		7,034
Commodity derivative instruments	0	0		8,633
Income taxes receivable	45,294	9,665		0
Prepayments and other current assets	0	221		42,762
Total current assets held for sale	53,224	24,581		83,132
Noncurrent assets:
Investments	0	37		37
Net property, plant and equipment	5,507	793,422		1,114,285
Deferred income taxes	61,347	127,655		141,556
Other	161	161		162
Less allowance for impairment of assets held for sale	938	754,541		756,127
Total noncurrent assets held for sale	66,077	166,734		499,913
Total assets held for sale	119,301	191,315		583,045
Current liabilities:
Accounts payable	175	25,013		32,375
Taxes payable	0	1,052		3,769
Deferred income taxes	4,120	3,620		4,955
Accrued compensation	0	13,080		5,982
Other accrued liabilities	3,084	4,838		11,820
Total current liabilities held for sale	7,379	47,603		58,901
Noncurrent liabilities:
Other	0	0		31,242
Total noncurrent liabilities held for sale	0	0		31,242
Total liabilities held for sale	$ 7,379	$ 47,603		$ 90,143
[1]	On the Company's Consolidated Balance Sheet, this amount was reclassified to a current deferred income tax liability and is reflected in current liabilities held for sale.
[2]	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.

Impairment fair value and ceili

Impairment fair value and ceiling test (Details 3) - Discontinued operations, held-for-sale or disposed of by sale [Member] - USD ($)	3 Months Ended				9 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2015
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
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)	$ 356,100,000		$ 756,100,000
Fair value impairment after tax	$ 600,000	$ (900,000)	$ 224,400,000		$ 476,400,000
Impairment of oil and gas properties				$ 500,400,000
Impairment of oil and gas properties, after tax				$ 315,300,000

Business exit costs (Details 4)

Business exit costs (Details 4) - Discontinued operations, held-for-sale or disposed of by sale [Member] - Exploration and production [Member] - USD ($)	3 Months Ended				9 Months Ended	12 Months Ended	15 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2016
Other restructuring [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business exit costs	$ 0		$ 300,000		$ 5,600,000	$ 2,500,000	$ 10,500,000
Contract termination [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business exit costs		$ 3,200,000		$ 3,300,000	$ 900,000

Reconciliation of income and ex

Reconciliation of income and expenses (Details 5) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss from discontinued operations	$ (5,400,000)	$ (223,112,000)	$ (299,538,000)	$ (816,517,000)
Loss from discontinued operations attributable to noncontrolling interest	0	(9,778,000)	(131,691,000)	(21,060,000)
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	162,000	140,428,000	122,894,000	288,537,000
Operating expenses	230,000	478,798,000	513,756,000	1,565,579,000
Operating loss	(68,000)	(338,370,000)	(390,862,000)	(1,277,042,000)
Other income	375,000	298,000	762,000	2,758,000
Interest expense	0	703,000	1,753,000	1,221,000
Income (loss) from discontinued operations before income taxes	307,000	(338,775,000)	(391,853,000)	(1,275,505,000)
Income taxes	5,707,000	(115,663,000)	(92,315,000)	(458,988,000)
Loss from discontinued operations	(5,400,000)	(223,112,000)	(299,538,000)	(816,517,000)
Loss from discontinued operations attributable to noncontrolling interest	0	(9,778,000)	(131,691,000)	(21,060,000)
Loss from discontinued operations attributable to the Company	(5,400,000)	(213,334,000)	(167,847,000)	(795,457,000)
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	$ 935,000	$ (8,600,000)	$ (253,000,000)	$ (18,400,000)

Goodwill rollforward (Details)

Goodwill rollforward (Details) - USD ($) $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Goodwill [Roll Forward]
Balance as of beginning of period	[1]	$ 635,204	$ 635,204	$ 635,204
Goodwill acquired during the year		6,323	0	0
Balance as of end of period	[1]	641,527	635,204	635,204
Natural gas distribution [Member]
Goodwill [Roll Forward]
Balance as of beginning of period		345,736	345,736	345,736
Goodwill acquired during the year		0	0	0
Balance as of end of period		345,736	345,736	345,736
Pipeline and midstream [Member]
Goodwill [Roll Forward]
Balance as of beginning of period	[1]	9,737	9,737	9,737
Goodwill acquired during the year		0	0	0
Balance as of end of period	[1]	9,737	9,737	9,737
Goodwill, impaired, accumulated impairment loss		12,300	12,300	12,300
Construction materials and contracting [Member]
Goodwill [Roll Forward]
Balance as of beginning of period		176,290	176,290	176,290
Goodwill acquired during the year		0	0	0
Balance as of end of period		176,290	176,290	176,290
Construction services [Member]
Goodwill [Roll Forward]
Balance as of beginning of period		103,441	103,441	103,441
Goodwill acquired during the year		6,323	0	0
Balance as of end of period		$ 109,764	$ 103,441	$ 103,441
[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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 6,529,000	$ 7,908,000	$ 6,529,000	$ 7,908,000	$ 7,342,000
Amortization of intangible assets	600,000	600,000	1,900,000	2,000,000
Estimated amortization expense for amortizable intangible assets [Abstract]
2,016	2,500,000		2,500,000
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
Thereafter	1,000,000		1,000,000
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	17,145,000	20,975,000	17,145,000	20,975,000	20,975,000
Intangible assets, accumulated amortization	(13,524,000)	(16,455,000)	(13,524,000)	(16,455,000)	(16,845,000)
Intangible assets, net (excluding goodwill)	3,621,000	4,520,000	3,621,000	4,520,000	4,130,000
Noncompete agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,430,000	4,409,000	2,430,000	4,409,000	4,409,000
Intangible assets, accumulated amortization	(1,622,000)	(3,632,000)	(1,622,000)	(3,632,000)	(3,655,000)
Intangible assets, net (excluding goodwill)	808,000	777,000	808,000	777,000	754,000
Other intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	7,764,000	8,300,000	7,764,000	8,300,000	8,304,000
Intangible assets, accumulated amortization	(5,664,000)	(5,689,000)	(5,664,000)	(5,689,000)	(5,846,000)
Intangible assets, net (excluding goodwill)	$ 2,100,000	$ 2,611,000	$ 2,100,000	$ 2,611,000	$ 2,458,000

Derivative instruments (Details

Derivative instruments (Details)	9 Months Ended
	Sep. 30, 2016USD ($)bblMMBTU	Dec. 31, 2015USD ($)bblMMBTU	Sep. 30, 2015USD ($)bblMMBTU
Derivative instruments [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months from AOCI into earnings	$ (400,000)
Oil swap and\or collar [Member]
Derivative instruments [Line Items]
Derivative, nonmonetary notional amount | bbl	0	0	552,000
Natural gas swap and\or collar [Member]
Derivative instruments [Line Items]
Derivative, nonmonetary notional amount | MMBTU	0	0	920,000
Interest rate swap [Member]
Derivative instruments [Line Items]
Derivative, notional amount	$ 0	$ 0	$ 0

Gains and losses on derivative

Gains and losses on derivative instruments (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative instruments [Line Items]
Amount of loss reclassified from accumulated other comprehensive loss into interest expense (effective portion), net of tax	$ 92	$ 100	$ 275	$ 299
Designated as hedging instrument [Member] | Interest rate derivatives designated as cash flow hedges [Member]
Derivative instruments [Line Items]
Amount of loss reclassified from accumulated other comprehensive loss into interest expense (effective portion), net of tax	92	100	275	299
Not designated as hedging instrument [Member] | Commodity derivatives [Member]
Derivative instruments [Line Items]
Amount of gain (loss) recognized in discontinued operations, before tax	$ 0	$ 9,607	$ 0	$ (9,702)

Derivative instruments (Detai57

Derivative instruments (Details 3) - Discontinued operations, held-for-sale or disposed of by sale [Member] $ in Thousands	Sep. 30, 2015USD ($)
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	$ 8,633
Commodity contract [Member] | Not designated as hedging instrument [Member] | Disposal group current assets held for sale [Member]
Derivatives, Fair Value [Line Items]
Other derivatives not designated as hedging instruments assets at fair value	$ 8,633

Subject to master netting agree

Subject to master netting agreements (Details 4) - Discontinued operations, held-for-sale or disposed of by sale [Member] $ in Thousands	Sep. 30, 2015USD ($)
Derivative instruments [Line Items]
Derivative asset, fair value, gross asset	$ 8,633
Commodity derivative instruments assets [Member]
Derivative instruments [Line Items]
Derivative asset, fair value, gross asset	8,633
Gross amount not offset	0
Derivative asset, fair value, net	8,633
Total assets [Member]
Derivative instruments [Line Items]
Derivative asset, fair value, gross asset	8,633
Gross amount not offset	0
Derivative asset, fair value, net	$ 8,633

Fair value measurements Insuran

Fair value measurements Insurance contracts (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Investments used to satisfy nonqualified benefit plans obligations	$ 72,800,000	$ 66,500,000	$ 72,800,000	$ 66,500,000	$ 67,500,000
Net unrealized gain (loss) of investments used to satisfy obligations under nonqualified benefit plans	$ 1,400,000	$ (1,700,000)	$ 5,300,000	$ 700,000

Available-for-sale securities (

Available-for-sale securities (Details 2) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Available-for-sale securities [Abstract]
Cost	$ 9,882	$ 10,443	$ 10,167
Gross unrealized gains	43	19	33
Gross unrealized losses	(17)	(55)	(22)
Fair value	9,908	10,407	10,178
Mortgage backed securities [Member]
Available-for-sale securities [Abstract]
Cost	9,882	9,128	7,843
Gross unrealized gains	43	19	29
Gross unrealized losses	(17)	(49)	(18)
Fair value	$ 9,908	9,098	7,854
US Treasury securities [Member]
Available-for-sale securities [Abstract]
Cost		1,315	2,324
Gross unrealized gains		0	4
Gross unrealized losses		(6)	(4)
Fair value		$ 1,309	$ 2,324

Fair value measurements (Detail

Fair value measurements (Details 3) - USD ($) $ in Thousands	Sep. 30, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015
Fair value measurements [Line Items]
Nonrecurring fair value measurement					$ 10,800		$ 1,100
Concentration risks, percentage [Abstract]
Percentage in fixed-income and other investments	65.00%		63.00%		65.00%
Percentage investment in common stock of large-cap companies	18.00%		19.00%		18.00%
Percentage investment in common stock of mid-cap companies	9.00%		9.00%		9.00%
Percentage investment in common stock of small-cap companies	6.00%		7.00%		6.00%
Percentage Investment in target date investments	1.00%		1.00%		1.00%
Percentage investment in cash and cash equivalents	1.00%		1.00%		1.00%
Fair value, measurements, recurring [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	$ 85,010		$ 79,286		$ 77,861
Fair value, measurements, recurring [Member] | Money market funds [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	2,284		1,420		1,219
Fair value, measurements, recurring [Member] | insurance contract [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	72,818	[1]	67,459	[2]	66,464	[3]
Fair value, measurements, recurring [Member] | Mortgage backed securities [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	9,908		9,098		7,854
Fair value, measurements, recurring [Member] | US Treasury securities [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure			1,309		2,324
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		0
Fair value, measurements, recurring [Member] | Fair value, inputs, level 2 [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	85,010		79,286		77,861
Fair value, measurements, recurring [Member] | Fair value, inputs, level 2 [Member] | Money market funds [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	2,284		1,420		1,219
Fair value, measurements, recurring [Member] | Fair value, inputs, level 2 [Member] | insurance contract [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure	72,818	[1]	67,459	[2]	66,464	[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	9,908		9,098		7,854
Fair value, measurements, recurring [Member] | Fair value, inputs, level 2 [Member] | US Treasury securities [Member]
Fair value measurements [Line Items]
Assets, fair value disclosure			1,309		2,324
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		$ 0
[1]	The insurance contract invests approximately 65 percent in fixed-income investments, 18 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.
[2]	The insurance contract invests approximately 63 percent in fixed-income investments, 19 percent in common stock of large-cap companies, 9 percent in common stock of mid-cap companies, 7 percent in common stock of small-cap companies, 1 percent in target date investments and 1 percent in cash equivalents.
[3]	The insurance contract invests approximately 65 percent in fixed-income investments, 18 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 (Deta62

Fair value measurements (Details 4) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Carrying amount [Member]
Fair value, balance sheet grouping [Line Items]
Long-term debt	$ 1,901,948	$ 1,796,163	$ 2,200,773
Fair value [Member]
Fair value, balance sheet grouping [Line Items]
Long-term debt, fair value	$ 2,047,339	$ 1,819,828	$ 2,277,074

Long-term debt (Details)

Long-term debt (Details) - Centennial Energy Holdings, Inc [Member] $ in Millions	Sep. 23, 2016USD ($)
Line of Credit Facility [Line Items]
Facility, decrease borrowing capacity	$ 150
Facility, maximum borrowing capacity	$ 500
Ratio of total debt to total capitalization as specified in debt convenants.	65.00%

Equity (Details)

Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Increase decrease in stockholders equity roll forward
Total stockholders' equity			$ 2,396,505
Noncontrolling interest			124,043
Balance			2,520,548	$ 3,249,784
Net income (loss)	$ 82,986	$ (149,226)	(132,988)	(696,029)
Other comprehensive income	315	402	(743)	2,259
Dividends declared on preferred stocks			(514)	(514)
Dividends declared on common stock			(109,858)	(106,714)
Stock-based compensation			2,955	2,266
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings			(323)
Excess tax benefit (net tax deficit) on stock-based compensation			(1,664)	(1,632)
Issuance of common stock				21,894
Contribution from noncontrolling interest			7,648	52,000
Distribution to noncontrolling interest				(8,443)
Total stockholders' equity	2,285,061	2,376,631	2,285,061	2,376,631
Noncontrolling interest	0	138,240	0	138,240
Balance	2,285,061	2,514,871	2,285,061	2,514,871
Total stockholders’ equity [Member]
Increase decrease in stockholders equity roll forward
Total stockholders' equity			2,396,505	3,134,041
Net income (loss) attributable to parent			(1,297)	(674,969)
Other comprehensive income			(743)	2,259
Dividends declared on preferred stocks			(514)	(514)
Dividends declared on common stock			(109,858)	(106,714)
Stock-based compensation			2,955	2,266
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings			(323)
Excess tax benefit (net tax deficit) on stock-based compensation			(1,664)	(1,632)
Issuance of common stock				21,894
Contribution from noncontrolling interest			0	0
Distribution to noncontrolling interest				0
Total stockholders' equity	2,285,061	2,376,631	2,285,061	2,376,631
Noncontrolling interest [Member]
Increase decrease in stockholders equity roll forward
Noncontrolling interest			124,043	115,743
Loss from discontinued operations attributable to noncontrolling interest			(131,691)	(21,060)
Other comprehensive income			0	0
Dividends declared on preferred stocks			0	0
Dividends declared on common stock			0	0
Stock-based compensation			0	0
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings			0
Excess tax benefit (net tax deficit) on stock-based compensation			0	0
Issuance of common stock				0
Contribution from noncontrolling interest			7,648	52,000
Distribution to noncontrolling interest				(8,443)
Noncontrolling interest	$ 0	$ 138,240	$ 0	$ 138,240

Business segment data (Details)

Business segment data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Revenues	$ 1,208,567	$ 1,198,342	$ 3,112,730	$ 2,997,225
Intersegment operating revenues	0	0	0	0
Earnings (loss) on common stock before loss from discontinued operations	88,215	73,715	166,036	119,974
Loss from discontinued operations, net of tax	(5,400)	(223,112)	(299,538)	(816,517)
Loss from discontinued operations attributable to noncontrolling interest	0	(9,778)	(131,691)	(21,060)
Earnings (loss) on common stock	82,815	(139,619)	(1,811)	(675,483)
Regulated operation [Member]
Segment Reporting Information [Line Items]
Revenues	192,079	185,417	783,997	807,585
Intersegment operating revenues	3,278	3,740	30,969	31,365
Earnings (loss) on common stock before loss from discontinued operations	5,564	5,699	53,021	45,696
Nonregulated operation [Member]
Segment Reporting Information [Line Items]
Revenues	1,016,488	1,012,925	2,328,733	2,189,640
Intersegment operating revenues	2,403	4,880	6,614	26,151
Earnings (loss) on common stock before loss from discontinued operations	77,052	62,775	107,416	70,771
Electric [Member] | Regulated operation [Member]
Segment Reporting Information [Line Items]
Revenues	82,156	74,604	238,911	210,646
Intersegment operating revenues	0	0	0	0
Earnings (loss) on common stock before loss from discontinued operations	12,699	12,605	31,840	26,842
Natural gas distribution [Member] | Regulated operation [Member]
Segment Reporting Information [Line Items]
Revenues	87,941	89,520	500,106	553,058
Intersegment operating revenues	0	0	0	0
Earnings (loss) on common stock before loss from discontinued operations	(12,524)	(12,298)	4,940	3,777
Pipeline and midstream [Member] | Regulated operation [Member]
Segment Reporting Information [Line Items]
Revenues	21,982	21,293	44,980	43,881
Intersegment operating revenues	3,278	3,740	30,969	31,365
Earnings (loss) on common stock before loss from discontinued operations	5,389	5,392	16,241	15,077
Pipeline and midstream [Member] | Nonregulated operation [Member]
Segment Reporting Information [Line Items]
Revenues	10,732	14,545	29,697	42,294
Intersegment operating revenues	41	145	161	460
Earnings (loss) on common stock before loss from discontinued operations	1,304	(8,587)	2,043	(8,498)
Construction materials and contracting [Member] | Nonregulated operation [Member]
Segment Reporting Information [Line Items]
Revenues	724,535	774,288	1,475,643	1,475,585
Intersegment operating revenues	155	244	370	2,450
Earnings (loss) on common stock before loss from discontinued operations	69,523	68,823	88,747	74,324
Construction services [Member] | Nonregulated operation [Member]
Segment Reporting Information [Line Items]
Revenues	280,801	223,676	822,226	670,594
Intersegment operating revenues	3	2,112	541	17,298
Earnings (loss) on common stock before loss from discontinued operations	7,234	4,742	20,198	16,505
Other [Member] | Nonregulated operation [Member]
Segment Reporting Information [Line Items]
Revenues	420	416	1,167	1,167
Intersegment operating revenues	2,204	2,379	5,542	5,943
Earnings (loss) on common stock before loss from discontinued operations	(1,009)	(2,203)	(3,572)	(11,560)
Intersegment eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment operating revenues	(5,681)	(8,620)	(37,583)	(57,516)
Earnings (loss) on common stock before loss from discontinued operations	$ 5,599	$ 5,241	$ 5,599	$ 3,507

Employee benefit plans (Details

Employee benefit plans (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension benefits [Member]
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	$ 0		$ 0	$ 0	$ 86,000
Interest cost	4,305,000		4,285,000	12,915,000	12,855,000
Expected return on assets	(5,231,000)		(5,563,000)	(15,693,000)	(16,689,000)
Amortization of prior service credit	0		0	0	36,000
Amortization of net actuarial loss	1,553,000		1,734,000	4,660,000	5,282,000
Curtailment loss				0	258,000
Net periodic benefit cost, including amount capitalized	627,000		456,000	1,882,000	1,828,000
Less amount capitalized	82,000		90,000	284,000	219,000
Net periodic benefit cost	545,000		366,000	1,598,000	1,609,000
Other postretirement benefits [Member]
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Service cost	412,000		454,000	1,236,000	1,362,000
Interest cost	922,000		902,000	2,766,000	2,705,000
Expected return on assets	(1,133,000)		(1,199,000)	(3,400,000)	(3,597,000)
Amortization of prior service credit	(343,000)		(343,000)	(1,029,000)	(1,028,000)
Amortization of net actuarial loss	371,000		511,000	1,118,000	1,525,000
Curtailment loss				0	0
Net periodic benefit cost, including amount capitalized	229,000		325,000	691,000	967,000
Less amount capitalized	(34,000)		36,000	4,000	98,000
Net periodic benefit cost	263,000		289,000	687,000	869,000
Supplemental employee retirement plans [Member]
Defined benefit plan disclosure, net periodic benefit cost [Line Items]
Curtailment loss		$ (3,300,000)
Net periodic benefit cost	$ 1,300,000		$ 1,700,000	$ 600,000	$ 5,300,000

Multiemployer plan (Details 2)

Multiemployer plan (Details 2) - Multiemployer plans, pension [Member] - Operating Engineers Local 800 and WY Contractors Association Pension Plan for WY [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2015	Sep. 30, 2016
Multiemployer Plans [Line Items]
Additional multiemployer plan withdrawal obligation	$ 2.4
Multiemployer plans, withdrawal obligation		$ 16.4

Regulatory matters (Details)

Regulatory matters (Details) - USD ($)

Oct. 27, 2016

Oct. 14, 2016

Oct. 06, 2016

Sep. 06, 2016

Aug. 12, 2016

Jul. 07, 2016

Jun. 15, 2016

Jun. 10, 2016

Jun. 01, 2016

Apr. 29, 2016

Mar. 09, 2016

Feb. 10, 2016

Jan. 05, 2016

Jan. 01, 2016

Dec. 01, 2015

Sep. 30, 2015

Jun. 30, 2015

SDPUC-Electric [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 2,700,000

Percent above current rates requested

19.20%

Interim rate increase (decrease), amount

$ 2,700,000

Rate increase approved

$ 1,400,000

SDPUC-Natural Gas [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 1,500,000

Percent above current rates requested

3.10%

Interim rate increase (decrease), amount

1,500,000

Rate increase approved

$ 1,200,000

MNPUC [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 1,600,000

Percent above current rates requested

6.40%

Interim rate increase (decrease), amount

$ 1,500,000

Rate increase approved

$ 1,100,000

Interim rate increase (decrease), percent

6.40%

Percent above current rates approved

5.20%

NDPSC-Renewable Rider [Member]

Regulatory matters [Line Items]

Interim rate increase (decrease), amount

$ 15,100,000

Return on equity, percentage

10.50%

NDPSC-Electric Rider [Member]

Regulatory matters [Line Items]

Interim rate increase (decrease), amount

$ 9,700,000

Return on equity, percentage

10.50%

NDPSC-Transmission Adjustment [Member]

Regulatory matters [Line Items]

Interim rate increase (decrease), amount

$ 6,800,000

Return on equity, percentage

10.50%

WUTC [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 10,500,000

Percent above current rates requested

4.20%

Rate increase approved

$ 4,000,000

OPUC [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 1,900,000

Percent above current rates requested

2.80%

WUTC-Pipeline Replacement [Member]

Regulatory matters [Line Items]

Replacement cost recovery mechanism

$ 4,600,000

Percent of additional revenue requested

2.00%

Incremental pipeline recovery investment

$ 2,400,000

Incremental operation and maintenance costs

$ 2,200,000

WYPSC [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 3,200,000

Percent above current rates requested

13.10%

IPUC [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 10,200,000

Percent above current rates requested

4.10%

Subsequent event [Member] | OPUC [Member]

Regulatory matters [Line Items]

Settlement agreement

$ 754,000

Subsequent event [Member] | WUTC-Pipeline Replacement [Member]

Regulatory matters [Line Items]

Incremental pipeline recovery investment, allowed amount

$ 1,900,000

Subsequent event [Member] | NDPSC [Member]

Regulatory matters [Line Items]

Rate increase requested

$ 13,400,000

Percent above current rates requested

6.60%

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

$ 13,000,000

Litigation (Details)

Litigation (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Loss Contingencies [Line Items]
Potential liabilities related to litigation and environmental matters	$ 20	$ 19.5	$ 21.4

Environmental matters (Details

Environmental matters (Details 2) - USD ($)	9 Months Ended
	Sep. 30, 2016	Jun. 08, 2016
Portland Harbor Site [Member]
Site Contingency [Line Items]
Environmental matters investigative costs	$ 100,000,000
Environmental matters, estimated costs		$ 746,000,000
Eugene, OR Manufactured Gas Plant Site [Member]
Site Contingency [Line Items]
Site contingency, low estimate, loss exposure	500,000
Site contingency, high estimate, loss exposure	$ 11,000,000
Estimated proportional share of cleanup liability	50.00%
Accrual for environmental loss contingencies	$ 1,700,000
Bremerton, WA Manufactured Gas Plant Site [Member]
Site Contingency [Line Items]
Site contingency, low estimate, loss exposure	340,000
Site contingency, high estimate, loss exposure	6,400,000
Accrual for environmental loss contingencies	12,700,000
Bellingham, WA Manufactured Gas Plant Site [Member]
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	$ 8,000,000

Guarantees (Details 3)

Guarantees (Details 3)	Sep. 30, 2016USD ($)
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 110,000,000
Fixed maximum amounts guaranteed by year 2016	4,200,000
Fixed maximum amounts guaranteed by year 2017	30,300,000
Fixed maximum amounts guaranteed by year 2018	12,000,000
Fixed maximum amounts guaranteed by year 2019	59,500,000
No scheduled maturity date	4,000,000
Amount outstanding under guarantees that is reflected on balance sheet	0
Letters of credit	34,900,000
Letters of credit set to expire - 2016	2,900,000
Letters of credit set to expire - 2017	32,000,000
Outstanding letters of credit	0
Amount of surety bonds outstanding	560,700,000
Financial guarantee [Member]
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 64,900,000

Commitment and contingencies va

Commitment and contingencies variable interest entities (Details 4) - USD ($) $ in Thousands	Sep. 30, 2016	Jun. 27, 2016	Dec. 31, 2015	Sep. 30, 2015	Feb. 07, 2013
Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Total project costs	$ 300,000
Portion of capital commitment	150,000
Partner portion of capital commitment	75,000
Excess capital commitments	300,000
Term loan for project debt financing	75,000
Dakota Prairie Refining, LLC [Member] | Cash and cash equivalents [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets			$ 851	$ 625
Dakota Prairie Refining, LLC [Member] | Accounts receivable [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets			7,693	14,648
Dakota Prairie Refining, LLC [Member] | Inventories [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets			13,176	12,354
Dakota Prairie Refining, LLC [Member] | Other current assets [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets			6,215	7,125
Dakota Prairie Refining, LLC [Member] | Total current assets [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets			27,935	34,752
Dakota Prairie Refining, LLC [Member] | Net property, plant and equipment [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets			425,123	428,383
Dakota Prairie Refining, LLC [Member] | Other [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets			9,626	5,052
Dakota Prairie Refining, LLC [Member] | Total deferred charges and other assets [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets			9,626	5,052
Dakota Prairie Refining, LLC [Member] | Total assets [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets			462,684	468,187
Dakota Prairie Refining, LLC [Member] | Short-term borrowings [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities			45,500	29,500
Dakota Prairie Refining, LLC [Member] | Long-term debt due within one year [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities			5,250	4,125
Dakota Prairie Refining, LLC [Member] | Accounts payable [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities			24,766	21,686
Dakota Prairie Refining, LLC [Member] | Taxes payable [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities			1,391	1,630
Dakota Prairie Refining, LLC [Member] | Accrued compensation [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities			938	1,059
Dakota Prairie Refining, LLC [Member] | Other accrued liabilities [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities			4,953	1,217
Dakota Prairie Refining, LLC [Member] | Total current liabilities [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities			82,798	59,217
Dakota Prairie Refining, LLC [Member] | Long-term debt [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities			63,750	64,875
Dakota Prairie Refining, LLC [Member] | Total liabilities [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities			$ 146,548	$ 124,092
Fuel contract [Member]
Variable Interest Entities [Line Items]
Variable interest entity, reporting entity involvement, maximum loss exposure, amount	$ 44,100
Calumet [Member]
Variable Interest Entities [Line Items]
Previous percentage of ownership					50.00%
WBI Energy [Member]
Variable Interest Entities [Line Items]
Previous percentage of ownership					50.00%
Percentage of ownership acquired		50.00%