Property, Plant and Equipment (Schedule of Recognized Impairments) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Mar. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Impairment of oil and gas Properties	$ 171,300	$ 171,296	$ 1,206,284	$ 1,206,300
Corporate
Property, Plant and Equipment [Line Items]
Impairment of oil and gas Properties		0	14,060
United States
Property, Plant and Equipment [Line Items]
Impairment of oil and gas Properties		0	1,152,515
Canada
Property, Plant and Equipment [Line Items]
Impairment of oil and gas Properties		171,296	0
Other Foreign
Property, Plant and Equipment [Line Items]
Impairment of oil and gas Properties		$ 0	$ 39,709