Summary Of Significant Accounting Policies (Narrative) (Details) $ in Thousands, in Billions			3 Months Ended	12 Months Ended
	Sep. 17, 2018 XAF ( )	Sep. 17, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 XAF ( ) $ / bbl / $	Dec. 31, 2018 USD ($) $ / bbl / $
Organization And Accounting Policies [Line Items]
Capitalized oil and gas property			$ 442,203		$ 409,367			$ 443,329
Deferred tax assets			50,195		1,260			$ 40,077
Exchange rate | / $							573.000	573.000
Other operating income (expense), net				$ 365	(84)	$ (266)
Inventory write-off				400
Asset retirement obligation, revision of estimate				(6,527)	703	(1)
Receivable balance, net					3,556			$ 11,907
Value added tax and other receivables, net			2,306		6,925			2,226
Gains on foreign currency transactions				100	500	30
Interest expense capitalized				$ 0	0	0
Monthly royalty rate, based on production at the published price				13.00%
Working interest of carried partner, percentage				7.50%
Future working interest of carried partner percentage				10.00%
Deferred tax assets, gross					154,465			131,012
Valuation allowance					153,205	211,800		$ 90,935
Change in valuation allowance				$ (16,500)	57,600
Derivative cap price | $ / bbl							74.00	74.00
Derivative floor price | $ / bbl							74.00	74.00
Cash paid to settle derivatives				700
Cash received to settle derivatives					200
Restatement Adjustment [Member]
Organization And Accounting Policies [Line Items]
Capitalized oil and gas property			18,612
Deferred tax assets			(18,612)
Accrued liabilities					(2,600)
Deferred Tax Liability, Understated [Member]
Organization And Accounting Policies [Line Items]
Amount misstated			$ 18,600
Gabon
Organization And Accounting Policies [Line Items]
Other operating income (expense), net				400	(300)	(300)
Receivable balance, gross |							6.9
Receivable balance, net |							2.3
Reduction of VAT receivable |	14.1
Reduction of VAT receivable, net	4.7	$ 4,200
Recoveries (allowances) of VAT receivable				$ 100	$ (400)	$ (700)
Office Equipment
Organization And Accounting Policies [Line Items]
Estimated useful life				5 years
Leasehold Improvements | Minimum
Organization And Accounting Policies [Line Items]
Estimated useful life				5 years
Leasehold Improvements | Maximum
Organization And Accounting Policies [Line Items]
Estimated useful life				7 years