Natural Gas and Oil Properties (Narrative) (Details)	3 Months Ended
	Mar. 31, 2019 derivative_position $ / bbl $ / MMBTU	Mar. 31, 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	3.07	3.00
Oil | West Texas Intermediate
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per barrel (in dollars per bbl)	63.00	49.94
NGL | West Texas Intermediate
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per barrel (in dollars per bbl)	17.65	14.90