Derivatives (Effect of Derivative Instruments in the Consolidated Statements of Operations) (Details) - USD ($) $ in Thousands	1 Months Ended	2 Months Ended	3 Months Ended							11 Months Ended	12 Months Ended
	Feb. 08, 2018	Mar. 31, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (loss) on derivative contracts		$ (22,600)	$ 52,800	$ (11,200)	$ (29,200)	$ (29,700)	$ (10,500)	$ 18,300	$ 30,200	$ (10,247)
Predecessor
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (loss) on derivative contracts	$ 6,663										$ 8,287	$ (40,460)
Derivatives Not Designated As Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (loss) on derivative contracts										(10,247)
Derivatives Not Designated As Hedging | Oil commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (loss) on derivative contracts										(3,559)
Derivatives Not Designated As Hedging | Natural gas commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (loss) on derivative contracts										(6,688)
Derivatives Not Designated As Hedging | Natural gas liquids commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (loss) on derivative contracts										$ 0
Derivatives Not Designated As Hedging | Predecessor
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (loss) on derivative contracts	6,663										8,287	(40,460)
Derivatives Not Designated As Hedging | Predecessor | Oil commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (loss) on derivative contracts	4,796										1,450	(36,572)
Derivatives Not Designated As Hedging | Predecessor | Natural gas commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (loss) on derivative contracts	1,867										7,288	(2,410)
Derivatives Not Designated As Hedging | Predecessor | Natural gas liquids commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (loss) on derivative contracts	$ 0										$ (451)	$ (1,478)