Selected Quarterly Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Effect of Fourth Quarter Events [Line Items]
Net (loss) gain									$ (6,693)	$ (38,511)
Net (loss) gain per share - basic and diluted									$ (0.08)	$ (0.63)
Weighted-average shares outstanding-basic and diluted									81,890	61,107
Quarterly Financial Information [Member]
Effect of Fourth Quarter Events [Line Items]
Oil and gas sales
Net (loss) gain	$ (1,591)	$ (1,619)	$ (1,313)	$ (2,170)	$ (31,800)	$ 781	$ (1,241)	$ (6,251)
Net (loss) gain per share - basic and diluted	$ (0.02)	$ (0.02)	$ (0.02)	$ (0.03)	$ (0.48)	$ 0.02	$ (0.02)	$ (0.11)
Weighted-average shares outstanding-basic and diluted	100,769	82,001	74,126	69,987	66,135	61,089	59,346	57,504