Summary of Significant Accounting Policies - Schedule of Gains and Losses from Derivative Financial Instruments (Detail) - USD ($) $ in Thousands	1 Months Ended	2 Months Ended	3 Months Ended	7 Months Ended	9 Months Ended
	Aug. 13, 2018	Sep. 30, 2018	Sep. 30, 2017	Aug. 13, 2018	Sep. 30, 2017
Derivative [Line Items]
Gain (loss) from derivative financial instruments		$ (2,015)
Predecessor
Derivative [Line Items]
Gain (loss) from derivative financial instruments	$ (83)		$ 1,430	$ 881	$ 14,585
Gain (Loss) from Derivative Financial Instruments | Natural Gas Price Derivatives
Derivative [Line Items]
Gain (loss) from derivative financial instruments		$ (2,015)
Gain (Loss) from Derivative Financial Instruments | Natural Gas Price Derivatives | Predecessor
Derivative [Line Items]
Gain (loss) from derivative financial instruments	$ (83)		$ 1,430	$ 881	$ 14,585