Natural Gas and Oil Properties (Narrative) (Details)	9 Months Ended
	Sep. 30, 2018 USD ($) item	Sep. 30, 2017 USD ($) item
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 | item	0	0
Natural Gas [Member] | Henry Hub [Member]
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per MMBtu	$ 2.91	$ 3.00
Oil [Member] | West Texas Intermediate [Member]
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per barrel	63.43	46.27
NGL [Member] | West Texas Intermediate [Member]
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per barrel	$ 17.47	$ 12.47