Supplemental Financial Data - Oil and Gas Producing Activities (unaudited) (Details 7)	12 Months Ended
	Dec. 31, 2018 USD_Bbl	Dec. 31, 2017 Per_Mcf
Oil (per Bbl) [Member]
Average Sales Price And Production Cost Per Unit [Abstract]
Weighted averaged adjusted prices	51.34	65.56
Natural Gas (per Mcf) [Member]
Average Sales Price And Production Cost Per Unit [Abstract]
Weighted averaged adjusted prices	3.10	2.98