Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Line Items]
Total capitalized exploratory well costs		$ 166,423	$ 148,500	$ 129,628	$ 130,514
Exploratory well costs capitalized more than one year		118,200
Proceeds from sales of property, plant and equipment		64,097		33
Gain on sale of assets		131,982		22
Impairment of assets				$ 95,088
Western Canada [Member]
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment	$ 49,000
Asset retirement obligation settled	85,900
Gain on sale of assets		132,400
Eagle Ford Shale [Member]
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment	$ 14,800
Gain on sale of assets		0
Brunei [Member]
Property Plant And Equipment [Line Items]
Exploratory well costs capitalized more than one year		64,500
Malaysia [Member]
Property Plant And Equipment [Line Items]
Exploratory well costs capitalized more than one year		$ 53,700
Redetermination expense			$ 39,000