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Asset Retirement Obligations Reconciliation of Asset Retirement Obligation Liability (Tables) | 12 Months Ended
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Dec. 31, 2015
Asset Retirement Obligation [Abstract] |
Schedule of Change in Asset Retirement Obligation [Table Text Block] | A reconciliation of the Company’s total asset retirement obligation liability is as follows:
| As of December 31,
| 2015 |  | 2014
| (in thousands)
Beginning asset retirement obligation | $ | 122,124 |  |  | $ | 121,186 |
Liabilities incurred | 14,471 |  |  | 13,506 |
Liabilities settled | (24,781 | ) |  | (11,372 | )
Accretion expense | 5,091 |  |  | 6,090 |
Revision to estimated cash flows | 23,969 |  |  | (7,286 | )
Ending asset retirement obligation | $ | 140,874 |  |  | $ | 122,124 |

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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859 + Details
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