Supplemental Oil and Gas Disclosures (Schedule of Prices Used for Standardized Measure of Discounted Future Cash Flows Relating to Proved Reserves Disclosure) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Natural Gas [Member]
Reserve Quantities [Line Items]
Full cost ceiling test, price per MMBtu	$ 3.10	$ 2.98	$ 2.48
Oil [Member]
Reserve Quantities [Line Items]
Full cost ceiling test, price per barrel	65.56	47.79	39.25
NGL [Member]
Reserve Quantities [Line Items]
Full cost ceiling test, price per barrel	$ 17.64	$ 14.41	$ 6.74