Acquisitions And Dispositions (Narrative) (Details) $ in Thousands, a in Millions				1 Months Ended				12 Months Ended
	Nov. 22, 2016	Mar. 14, 2016 USD ($)	Jan. 01, 2014	Apr. 30, 2017 USD ($)	Dec. 31, 2016 USD ($) item	Oct. 31, 2014 item	Nov. 30, 2006 a item	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Apr. 30, 2014 USD ($)
Business Acquisition [Line Items]
Proceeds from the sale of oil and gas properties								$ 250	$ 830	$ 398
Gain from sale of property								300
Allowance for accounts with partners					$ 500			$ 500	500
Offshore Gabon [Member]
Business Acquisition [Line Items]
Production license agreement term extended by government								5 years
Hefley Field [Member]
Business Acquisition [Line Items]
Proceeds received from sale of property					$ 800
Number of wells, interest for sale | item					2
East Poplar Dome Field [Member]
Business Acquisition [Line Items]
Proceeds from the sale of oil and gas properties				$ 300
Joint Operating With Republic Of Angola [Member]
Business Acquisition [Line Items]
Primary term of the production sharing contract								4 years
Optional term of extension of production sharing contract								3 years
Area under acquire property exploration rights agreement term (acres) | a							1.4
Number of exploration wells | item							2
Number Of Additional Exploration Wells | item						2
Joint operation agreement related to third party in working interest percentage							40.00%
Additional joint operation agreement related to third party in working interest percentage							10.00%
Stipulated payment for each exploration well, under PSA terms								$ 10,000
Drilling commitment, net								5,000
Liability for the penalty					$ 15,000			$ 15,000	15,000
Allowance for accounts with partners											$ 7,600
Working interest ownership other, percentage			40.00%
Sojitz [Member]
Business Acquisition [Line Items]
Percentage of working interest	2.98%
Percentage of participating interest	3.23%
Actual impact on revenue from acquisition									$ 200
Sonangol P&P [Member]
Business Acquisition [Line Items]
Payment from joint venture partners		$ 19,000
Reversal of allowance		7,600
Interest income		$ 3,200