Fair Value Measurements (Fair Value Hierarchy for Net Assets and Liabilities Measured Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value	$ 26,613
Derivative liability, fair value	3,827
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI	47,082
Assets, fair value disclosure	73,695
Recurring basis | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value	26,613
Derivative liability, fair value	3,827
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI	47,082
Assets, fair value disclosure	47,082
Recurring basis | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	26,613
Recurring basis | Significant Other Observable Inputs (Level 2) | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value	26,613
Derivative liability, fair value	$ 3,827
Predecessor
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value		$ 3,402
Derivative liability, fair value		746
Predecessor | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		3,402
Derivative liability, fair value		746
Predecessor | Recurring basis | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value		2,696
Derivative liability, fair value		721
Predecessor | Recurring basis | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value		706
Derivative liability, fair value		25
Predecessor | Recurring basis | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		3,402
Derivative liability, fair value		746
Predecessor | Recurring basis | Significant Other Observable Inputs (Level 2) | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value		2,696
Derivative liability, fair value		721
Predecessor | Recurring basis | Significant Other Observable Inputs (Level 2) | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value		706
Derivative liability, fair value		$ 25