Property, Plant and Equipment (Schedule of Recognized Impairments) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Impairment Expense	$ 20,000,000	$ 0	$ 95,088,000	[1]
United States Onshore [Member]
Property Plant And Equipment [Line Items]
Impairment Expense	$ 20,000,000
Canada [Member]
Property Plant And Equipment [Line Items]
Impairment Expense			$ 95,088,000

[1] Reclassified to conform to current presentation (see Note B).