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Discontinued operations (Tables) | 12 Months Ended
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Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |
Disposal Groups, Including Discontinued Operations [Table Text Block] | The carrying amounts of the major classes of assets and liabilities that are classified as held for sale on the Company's Consolidated Balance Sheets at December 31 were as follows:
| 2015 |  | 2014 |
| (In thousands)
Assets |  |
Current assets: |  |
Receivables, net | $ | 13,387 |  | $ | 94,132 |
Inventories | 1,308 |  | 11,401 |
Commodity derivative instruments | — |  | 18,335 |
Prepayments and other current assets | 9,886 |  | 7,309 |
Total current assets held for sale | 24,581 |  | 131,177 |
Noncurrent assets: |  |
Investments | 37 |  | 37 |
Net property, plant and equipment | 793,422 |  | 1,618,099 |
Deferred income taxes | 127,655 |  | — |
Other | 161 |  | 2,334 |
Less allowance for impairment of assets held for sale | 754,541 |  | — |
Total noncurrent assets held for sale | 166,734 |  | 1,620,470 |
Total assets held for sale | $ | 191,315 |  | $ | 1,751,647 |
Liabilities |  |
Current liabilities: |  |
Long-term debt due within one year | $ | — |  | $ | 897 |
Accounts payable | 25,013 |  | 103,556 |
Taxes payable | 1,052 |  | 19,900 |
Deferred income taxes | 3,620 |  | 8,206 |
Accrued compensation | 13,080 |  | 5,373 |
Other accrued liabilities | 4,838 |  | 16,796 |
Total current liabilities held for sale | 47,603 |  | 154,728 |
Noncurrent liabilities: |  |
Deferred income taxes | — |  | 238,391 |
Other liabilities | — |  | 57,050 |
Total noncurrent liabilities held for sale | — |  | 295,441 |
Total liabilities held for sale | $ | 47,603 |  | $ | 450,169 |
Reconciliation of Major Classes of Income And Expense [Table Text Block] | The reconciliation of the major classes of income and expense constituting pretax income (loss) from discontinued operations to the after-tax net income (loss) from discontinued operations of the Company's Consolidated Statements of Income at December 31 were as follows:
| 2015 |  | 2014 |  | 2013 |
| (In thousands)
Operating revenues | $ | 184,853 |  | $ | 547,571 |  | $ | 536,023 |
Operating expenses | 1,423,037 |  | 378,891 |  | 364,120 |
Operating income (loss) | (1,238,184 | ) | 168,680 |  | 171,903 |
Other income | 2,374 |  | 1,163 |  | 549 |
Interest expense | 235 |  | 110 |  | 114 |
Income (loss) from discontinued operations before income taxes | (1,236,045 | ) | 169,733 |  | 172,338 |
Income taxes | (463,660 | ) | 54,558 |  | 62,459 |
Income (loss) from discontinued operations | $ | (772,385 | ) | $ | 115,175 |  | $ | 109,879 |

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- Definition Tabular disclosure of information related to a disposal group. Includes, but is not limited to, a discontinued operation, disposal classified as held-for-sale or disposed of by means other than sale or disposal of an individually significant component. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=51716988&loc=SL51721533-107759 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 4B -URI http://asc.fasb.org/extlink&oid=51717284&loc=SL51721665-107760 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=51717284&loc=d3e1474-107760 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=51717284&loc=d3e1361-107760 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=51717284&loc=SL51721683-107760 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 3A -URI http://asc.fasb.org/extlink&oid=51719941&loc=SL51724579-110230 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5C -URI http://asc.fasb.org/extlink&oid=51717284&loc=SL51721675-107760 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 4A -URI http://asc.fasb.org/extlink&oid=51717284&loc=SL51721663-107760 Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=51719941&loc=d3e2941-110230 Reference 10: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5B -URI http://asc.fasb.org/extlink&oid=51717284&loc=SL51721673-107760 Reference 11: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 3A -URI http://asc.fasb.org/extlink&oid=51717284&loc=SL51721659-107760 Reference 12: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5A -URI http://asc.fasb.org/extlink&oid=51717284&loc=SL51721671-107760 Reference 13: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5D -URI http://asc.fasb.org/extlink&oid=51717284&loc=SL51721677-107760 + Details
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