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Asset Retirement Obligations - Reconciliation of Beginning and Ending Aggregate Carrying Amounts of Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Asset Retirement Obligation, Roll Forward Analysis      
Beginning balance $ 54,402 $ 424,117 $ 498,410
Liability incurred upon acquiring and drilling wells 1,662 4,968 5,078
Revisions in estimated cash flows 44,060 (5,848) (3,077)
Liability settled or disposed in current period (1,023) (377,927) (113,071)
Accretion 4,477 9,092 36,777
Ending balance 103,578 54,402 424,117
Less: current portion 8,399 0 87,063
Asset retirement obligations, net of current $ 95,179 $ 54,402 $ 337,054