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Segment Information Reconciliation of Segment Information, Revenue and Other Operating Income (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Revenue, Major Customer [Line Items]    
Total Segment Revenue from Contracts with External Customers $ 405,623 $ 317,763
Gain (Loss) on Commodity Derivative Instruments 35,087 (22,463)
Other Operating Income 10,710 15,650
Total Consolidated Revenue and Other Operating Income 495,729 319,929
Operating Segments [Member]    
Revenue, Major Customer [Line Items]    
Total Segment Revenue from Contracts with External Customers $ 449,932 $ 326,742