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Acquisitions (Details) a in Thousands, $ in Thousands |  |  | 12 Months Ended
--- | --- | --- | ---
Oct. 15, 2014 USD ($) | Sep. 24, 2014 USD ($) a | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) a | Dec. 31, 2013 USD ($)
Business Acquisition [Line Items] |  |  |  |  |
Proved Oil and Gas Property, Successful Effort Method |  |  | $ 7,606,405 | $ 7,348,436 |
Unproved Oil and Gas Property, Successful Effort Method |  |  | 284,538 | 532,498 |
Asset Retirement Obligations, Noncurrent |  |  | (137,525) | (120,867) |
Payments to Acquire Oil and Gas Property and Equipment |  |  | $ 7,984 | 544,553 | $ 61,603
Gooseneck Prospect Acquisition 2014 [Member] |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Net acres acquired | a |  | 61 |  |  |
Payments to Acquire Businesses, Gross |  | $ 321,807 |  |  |
Proved Oil and Gas Property, Successful Effort Method |  | 203,467 |  |  |
Unproved Oil and Gas Property, Successful Effort Method |  | 126,588 |  |  |
Oil and Gas Property, Successful Effort Method, Net |  | 330,055 |  |  |
Working Capital Acquired |  | (6,135) |  |  |
Asset Retirement Obligations, Noncurrent |  | (2,113) |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net |  | $ 321,807 |  |  |
Gooseneck Second Prospect Acquisition 2014 [Member] |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Payments to Acquire Businesses, Gross | $ 84,836 |  |  |  |
Proved Oil and Gas Property, Successful Effort Method | 54,612 |  |  |  |
Unproved Oil and Gas Property, Successful Effort Method | 29,610 |  |  |  |
Oil and Gas Property, Successful Effort Method, Net | 84,222 |  |  |  |
Working Capital Acquired | 2,232 |  |  |  |
Asset Retirement Obligations, Noncurrent | (1,618) |  |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net | $ 84,836 |  |  |  |
Rocky Mountain Acquisition 2014 [Member] |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Payments to Acquire Oil and Gas Property and Equipment |  |  |  | $ 135,500 |
Leasehold Acres Consideration to Acquire Unproved Property | a |  |  |  | 7 |

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