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Summary of significant accounting policies (Tables) | 12 Months Ended
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Dec. 31, 2017
Accounting Policies [Abstract] |
Inventories | Inventories at December 31 consisted of:
| 2017 |  | 2016 |
| (In thousands)
Aggregates held for resale | $ | 115,268 |  | $ | 115,471 |
Asphalt oil | 30,360 |  | 29,103 |
Natural gas in storage (current) | 20,950 |  | 25,761 |
Materials and supplies | 18,650 |  | 18,372 |
Merchandise for resale | 14,905 |  | 16,437 |
Other | 26,450 |  | 33,129 |
Total | $ | 226,583 |  | $ | 238,273 |
AFUDC and interest capitailized | The amount of AFUDC and interest capitalized for the years ended December 31 were as follows:
| 2017 |  | 2016 |  | 2015 |
|  | (In thousands) |  |
Interest capitalized | $ | — |  | $ | — |  | $ | 4,381 |
AFUDC - borrowed | $ | 966 |  | $ | 914 |  | $ | 4,907 |
AFUDC - equity | $ | 909 |  | $ | 565 |  | $ | 7,971 |
Property, plant and equipment | Property, plant and equipment at December 31 was as follows:
| 2017 |  | 2016 |  | Weighted Average Depreciable Life in Years |
| (Dollars in thousands, where applicable)
Regulated: |  |  |
Electric: |  |  |
Generation | $ | 1,034,765 |  | $ | 1,036,373 |  | 39 |
Distribution | 415,543 |  | 398,382 |  | 44 |
Transmission | 296,941 |  | 284,048 |  | 57 |
Construction in progress | 117,906 |  | 62,212 |  | — |
Other | 117,109 |  | 107,598 |  | 15 |
Natural gas distribution: |  |  |
Distribution | 1,831,795 |  | 1,718,633 |  | 47 |
Construction in progress | 19,823 |  | 19,934 |  | — |
Other | 468,227 |  | 440,846 |  | 18 |
Pipeline and midstream: |  |  |
Transmission | 516,932 |  | 490,143 |  | 53 |
Gathering | 37,837 |  | 37,831 |  | 20 |
Storage | 45,629 |  | 45,350 |  | 62 |
Construction in progress | 17,488 |  | 16,507 |  | — |
Other | 41,054 |  | 40,873 |  | 33 |
Nonregulated: |  |  |
Pipeline and midstream: |  |  |
Gathering and processing | 31,678 |  | 31,682 |  | 19 |
Construction in progress | 17 |  | 13 |  | — |
Other | 9,649 |  | 9,800 |  | 10 |
Construction materials and contracting: |  |  |
Land | 95,745 |  | 94,625 |  | — |
Buildings and improvements | 102,435 |  | 102,347 |  | 20 |
Machinery, vehicles and equipment | 947,979 |  | 930,471 |  | 12 |
Construction in progress | 7,750 |  | 16,181 |  | — |
Aggregate reserves | 406,139 |  | 405,751 |  | * |
Construction services: |  |  |
Land | 5,216 |  | 5,346 |  | — |
Buildings and improvements | 27,351 |  | 26,693 |  | 25 |
Machinery, vehicles and equipment | 137,924 |  | 132,217 |  | 6 |
Other | 6,774 |  | 7,105 |  | 4 |
Other: |  |  |
Land | 2,837 |  | 2,837 |  | — |
Other | 28,286 |  | 46,431 |  | 19 |
Less accumulated depreciation, depletion and amortization | 2,691,641 |  | 2,578,902 |  |
Net property, plant and equipment | $ | 4,079,188 |  | $ | 3,931,327 |  |
* | Depleted on the units-of-production method based on recoverable aggregate reserves.
Percentage-of-completion method | Costs and estimated earnings in excess of billings and billings in excess of costs and estimated earnings on uncompleted contracts at December 31 were as follows:
| 2017 |  | 2016 |
| (In thousands)
Costs and estimated earnings in excess of billings on uncompleted contracts | $ | 109,541 |  | $ | 64,558 |
Billings in excess of costs and estimated earnings on uncompleted contracts | $ | 84,123 |  | $ | 64,832 |
Amounts representing balances billed but not paid by customers under retainage provisions in contracts at December 31 were as follows:
| 2017 |  | 2016 |
| (In thousands)
Short-term retainage* | $ | 57,134 |  | $ | 45,109 |
Long-term retainage** | 1,410 |  | 1,506 |
Total retainage | $ | 58,544 |  | $ | 46,615 |
* | Expected to be paid within one year or less and included in receivables, net.
** | Included in deferred charges and other assets - other.
Schedule of earnings per share reconciliation | A reconciliation of the weighted average common shares outstanding used in the basic and diluted earnings (loss) per share calculation was as follows:
| 2017 |  | 2016 |  | 2015 |
|  | (In thousands) |  |
Weighted average common shares outstanding - basic | 195,304 |  | 195,299 |  | 194,928 |
Effect of dilutive performance share awards | 383 |  | 319 |  | 58 |
Weighted average common shares outstanding - diluted | 195,687 |  | 195,618 |  | 194,986 |
Shares excluded from the calculation of diluted earnings per share | — |  | — |  | — |
After-tax changes in the components of accumulated other comprehensive income (loss) | The after-tax changes in the components of accumulated other comprehensive loss as of December 31, 2017, 2016 and 2015, were as follows:
| Net Unrealized Gain (Loss) on Derivative Instruments Qualifying as Hedges |  | Post- retirement Liability Adjustment |  | Foreign Currency Translation Adjustment |  | Net Unrealized Gain (Loss) on Available- for-sale Investments |  | Total Accumulated Other Comprehensive Loss |
|  |  | (In thousands) |  |  |
Balance at December 31, 2015 | $ | (2,667 | ) | $ | (34,257 | ) | $ | (200 | ) | $ | (24 | ) | $ | (37,148 | )
Other comprehensive income (loss) before reclassifications | — |  | (1,470 | ) | 51 |  | (182 | ) | (1,601 | )
Amounts reclassified from accumulated other comprehensive loss | 367 |  | 2,506 |  | — |  | 143 |  | 3,016 |
Net current-period other comprehensive income (loss) | 367 |  | 1,036 |  | 51 |  | (39 | ) | 1,415 |
Balance at December 31, 2016 | (2,300 | ) | (33,221 | ) | (149 | ) | (63 | ) | (35,733 | )
Other comprehensive loss before reclassifications | — |  | (1,812 | ) | (6 | ) | (139 | ) | (1,957 | )
Amounts reclassified from accumulated other comprehensive loss | 366 |  | 1,013 |  | — |  | 120 |  | 1,499 |
Amounts reclassified to accumulated other comprehensive loss from a regulatory asset | — |  | (1,143 | ) | — |  | — |  | (1,143 | )
Net current-period other comprehensive income (loss) | 366 |  | (1,942 | ) | (6 | ) | (19 | ) | (1,601 | )
Balance at December 31, 2017 | $ | (1,934 | ) | $ | (35,163 | ) | $ | (155 | ) | $ | (82 | ) | $ | (37,334 | )
Reclassification out of accumulated other comprehensive income (loss) | Reclassifications out of accumulated other comprehensive loss for the years ended December 31 were as follows:
| 2017 |  | 2016 |  | Location on Consolidated Statements of Income
| (In thousands) |
Reclassification adjustment for loss on derivative instruments included in net income (loss): |  |  |
Interest rate derivative instruments | $ | (590 | ) | $ | (593 | ) | Interest expense
| 224 |  | 226 |  | Income taxes
| (366 | ) | (367 | ) |
Amortization of postretirement liability losses included in net periodic benefit cost (credit) | (1,658 | ) | (3,931 | ) | (a)
| 645 |  | 1,425 |  | Income taxes
| (1,013 | ) | (2,506 | ) |
Reclassification adjustment for loss on available-for-sale investments included in net income (loss) | (185 | ) | (220 | ) | Other income
| 65 |  | 77 |  | Income taxes
| (120 | ) | (143 | ) |
Total reclassifications | $ | (1,499 | ) | $ | (3,016 | ) |
(a) | Included in net periodic benefit cost (credit). For more information, see Note 14.

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