Property, Plant and Equipment Aging of Capitalized Exploratory Well Costs - (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) well project	Mar. 31, 2019 USD ($) well project	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 178,433	$ 227,126	$ 217,326	$ 207,855
No. of Wells (in wells) | well	11	9
No. of Projects (in projects) | project	5	4
Zero to one year
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 24,637	$ 78,016
No. of Wells (in wells) | well	3	3
No. of Projects (in projects) | project	3	2
One to two years
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 31,541	$ 0
No. of Wells (in wells) | well	2	0
No. of Projects (in projects) | project	2	0
Two to three years
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 0	$ 27,270
No. of Wells (in wells) | well	0	1
No. of Projects (in projects) | project	0	1
Three years or more
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 122,255	$ 121,840
No. of Wells (in wells) | well	6	5
No. of Projects (in projects) | project	0	1