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Fair Value Measurements - Reconciliation of Fair Value Measurements for Commodity Derivative Contracts (Details) - Commodity derivatives contracts - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Level 3 Fair Value Measurements - Commodity Derivative Contracts      
Beginning balance $ 350 $ 0 $ (512)
Loss on commodity derivative contracts (350) 0 (133)
Purchases (1,748) 350 0
Settlements paid 0 0 645
Level 3 commodity derivative contracts at December 31 $ (1,748) $ 350 $ 0