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Derivative Instruments (Details) - Successor - Not Designated as Hedging Instrument - Natural gas swap contracts $ in Thousands, BTU in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2017 USD ($) BTU | Dec. 31, 2016 USD ($) BTU
Commodity Contract, Maturity Q4 2017 |  |
Derivative [Line Items] |  |
Derivative energy measure (in BTUs) | BTU | 1,980 | 7,920
Commodity Contract, Maturity Q4 2018 |  |
Derivative [Line Items] |  |
Derivative energy measure (in BTUs) | BTU | 2,400 |
Commodity Contract |  |
Derivative [Line Items] |  |
Natural gas swap contracts, asset | $ 300 |
Natural gas swap contracts, current asset | 250 |
Natural gas swap contracts, noncurrent asset | $ 50 |
Natural gas swap contracts, current liability |  | $ 3,800

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