Revenue Recognition Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Oil and gas sales	$ 51,347	$ 45,782	$ 104,099	$ 88,194
Oil sales [Member]
Disaggregation of Revenue [Line Items]
Oil, natural gas and NGL sales	9,638	6,527	21,078	13,728
Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Oil, natural gas and NGL sales	36,369	35,043	72,136	66,106
NGL sales [Member]
Disaggregation of Revenue [Line Items]
Oil, natural gas and NGL sales	5,339	4,215	10,900	8,363
Other sales [Member]
Disaggregation of Revenue [Line Items]
Oil, natural gas and NGL sales	$ 0	$ (3)	$ (14)	$ (3)