Financial Instruments - Schedule of Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Oil and Natural Gas Derivatives
Debt Instrument [Line Items]
Carrying Amount	$ (156,941)	$ (67,814)
Fair Value	(156,941)	(67,814)
12.00% Second-Priority Senior Secured Notes – due January 2026
Debt Instrument [Line Items]
Carrying Amount	581,728
Fair Value	636,012
11.00% Second-Priority Senior Secured Notes – due April 2022
Debt Instrument [Line Items]
Carrying Amount		343,579
Fair Value		355,935
7.50% Senior Notes – due May 2022
Debt Instrument [Line Items]
Carrying Amount	6,060	6,060
Fair Value	3,333	5,238
Bank Credit Facility – matures May 2022
Debt Instrument [Line Items]
Carrying Amount	461,577	635,873
Fair Value	$ 465,000	$ 640,000