Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 264,498	$ 223,091	$ 715,218	$ 620,539
Lease bonus - mineral acreage	1,711	0	1,711	0
Realized gain (loss) on derivatives	3,346	5,424	7,781	(1,322)
Unrealized gain (loss) on derivatives	9,847	(21,337)	(29,715)	(9,492)
Total revenue	279,402	207,178	694,995	609,725
Oil revenues
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	198,302	169,913	541,590	484,343
Natural gas revenues
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	31,075	46,369	92,116	122,912
Third-party midstream services revenues
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	15,257	6,809	41,454	13,284
Sales of purchased natural gas
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	19,864	0	40,058	0
Lease bonus - mineral acreage	1,711		1,711
Total revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 264,498	$ 223,091	$ 715,218	$ 620,539