Derivative Instruments - Gain (Loss) on Derivatives (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2018
Realized gain (loss) on derivatives
Total realized gain (loss) on derivatives	$ (14,496)	$ (15,482)	$ 74
Unrealized gain (loss) on derivatives
Total unrealized gain (loss) on derivatives	(51,050)	108,015	(16,779)
Commodity derivative options
Realized gain (loss) on derivatives
Total realized gain (loss) on derivatives	5,571	(83)	172
Unrealized gain (loss) on derivatives
Total unrealized gain (loss) on derivatives	(19,611)	28,965	313
Commodity derivative swaps
Realized gain (loss) on derivatives
Total realized gain (loss) on derivatives	(20,245)	(15,399)	45
Unrealized gain (loss) on derivatives
Total unrealized gain (loss) on derivatives	(31,053)	79,121	(16,866)
Interest rate swaps
Realized gain (loss) on derivatives
Total realized gain (loss) on derivatives	178	0	(143)
Unrealized gain (loss) on derivatives
Total unrealized gain (loss) on derivatives	(666)	0	(226)
Series B Preferred Stock bifurcated derivative
Unrealized gain (loss) on derivatives
Total unrealized gain (loss) on derivatives	$ 280	$ (71)	$ 0