Property, Plant and Equipment (Narrative) (Details) $ in Thousands	1 Months Ended	6 Months Ended	12 Months Ended
	Jul. 31, 2019 USD ($) business	Jun. 30, 2020 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Well costs		$ 180,135		$ 217,326	$ 245,017	$ 207,855
Exploratory well costs capitalized more than one year		155,700
Impairment of oil and gas Properties		987,146
Athabasca Oil Corporation | Canadian Subsidiary
Property, Plant and Equipment [Line Items]
Cost of acquired assets, carried interest			$ 168,000
Malaysia Subsidiaries
Property, Plant and Equipment [Line Items]
Number of businesses divested (in businesses) | business	2
Cash received from divestiture	$ 2,000,000
Gain (loss) on disposition of business	960,000
Contingent bonus payment	$ 100,000
Vietnam
Property, Plant and Equipment [Line Items]
Exploratory well costs capitalized more than one year		87,600
United States
Property, Plant and Equipment [Line Items]
Exploratory well costs capitalized more than one year		27,400
Impairment of oil and gas Properties		947,437
Brunei
Property, Plant and Equipment [Line Items]
Exploratory well costs capitalized more than one year		25,200
MEXICO
Property, Plant and Equipment [Line Items]
Exploratory well costs capitalized more than one year		$ 15,500
Kaybob Duvernay Lands, Alberta | Canadian Subsidiary
Property, Plant and Equipment [Line Items]
Interest in assets acquired			70.00%
Placid Montney Lands, Alberta | Canadian Subsidiary
Property, Plant and Equipment [Line Items]
Interest in assets acquired			30.00%