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Summary of Significant Accounting Policies (Tables) | 9 Months Ended
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Sep. 30, 2018
Accounting Standards Update 2016-15, 2016-18 [Member] |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |
Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] | The accompanying unaudited condensed consolidated statements of cash flows (“accompanying statements of cash flows”) line items that were adjusted as a result of the adoption of ASU 2016-15 and ASU 2016-18 for the nine months ended September 30, 2017, are summarized as follows:
| For the Nine Months Ended September 30, 2017
| As Reported |  | As Adjusted
| (in thousands)
Cash flows from operating activities: |  |  |
Non-cash (gain) loss on extinguishment of debt, net | $ | 22 |  |  | N/A |
Loss on extinguishment of debt | N/A |  |  | $ | 35 |
Net cash provided by operating activities | $ | 370,597 |  |  | $ | 370,610 |
Cash flows from investing activities: |  |  |
Acquisition deposit held in escrow | $ | 3,000 |  |  | N/A |
Net cash provided by (used in) investing activities | $ | 69,007 |  |  | $ | 66,007 |
Cash flows from financing activities: |  |  |
Cash paid for extinguishment of debt (1) | N/A |  |  | $ | (13 | )
Net cash used in financing activities | $ | (7,561 | ) |  | $ | (7,574 | )
Net change in cash and cash equivalents | $ | 432,043 |  |  | N/A |
Net change in cash, cash equivalents, and restricted cash | N/A |  |  | $ | 429,043 |
Cash and cash equivalents at beginning of period | $ | 9,372 |  |  | N/A |
Cash, cash equivalents, and restricted cash at beginning of period | N/A |  |  | $ | 12,372 |
Cash and cash equivalents at end of period | $ | 441,415 |  |  | N/A |
Cash, cash equivalents, and restricted cash at end of period | N/A |  |  | $ | 441,415 |
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(1) | Included as a component within the cash paid to repurchase Senior Notes, including premium line item on the accompanying statements of cash flows.
Accounting Standards Update 2017-07 [Member] |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |
Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] | The accompanying statements of operations line items that were adjusted as a result of the adoption of ASU 2017-07 for the three and nine months ended September 30, 2017, are summarized as follows:
| For the Three Months Ended September 30, 2017 |  | For the Nine Months Ended September 30, 2017
| As Reported |  | As Adjusted |  | As Reported |  | As Adjusted
| (in thousands)
Operating expenses: |  |  |  |  |  |  |
Exploration | $ | 14,243 |  |  | $ | 14,119 |  |  | $ | 39,293 |  |  | $ | 38,919 |
General and administrative | $ | 27,880 |  |  | $ | 27,564 |  |  | $ | 85,564 |  |  | $ | 84,618 |
Total operating expenses | $ | 380,971 |  |  | $ | 380,531 |  |  | $ | 856,475 |  |  | $ | 855,155 |
Income (loss) from operations | $ | (85,592 | ) |  | $ | (85,152 | ) |  | $ | (67,637 | ) |  | $ | (66,317 | )
Other non-operating income, net | $ | 1,301 |  |  | $ | 861 |  |  | $ | 2,901 |  |  | $ | 1,581 |

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