Natural Gas and Oil Properties (Narrative) (Details)	6 Months Ended
	Jun. 30, 2019 derivative_position $ / bbl $ / MMBTU	Jun. 30, 2018 derivative_position $ / bbl $ / MMBTU
Natural Gas and Oil Properties [Line Items]
Natural gas, oil and NGL reserves discount	10.00%
Period of time needed to calculate ceiling value of reserves	12 months
Number of hedge positions designated for hedge accounting | derivative_position	0	0
Natural Gas | Henry Hub
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per MMBtu (in dollars per MMBtu) | $ / MMBTU	3.02	2.92
Oil | West Texas Intermediate
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per barrel (in dollars per bbl)	61.39	54.15
NGL | West Texas Intermediate
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per barrel (in dollars per bbl)	16.35	15.56