Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended					9 Months Ended
	Jan. 31, 2017	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Apr. 01, 2017	Dec. 31, 2015
Property Plant And Equipment [Line Items]
Total capitalized exploratory well costs		$ 178,384		$ 148,500	$ 128,156		$ 178,384	$ 128,156		$ 130,514
Exploratory well costs capitalized more than one year		136,800					136,800
Proceeds from sales of property, plant and equipment							69,146	1,154,623
Gain (loss) on sale of assets		117			$ (730)		$ 130,765	3,101
Impairment of assets								95,088
Cost of acquired assets, cash paid						$ 206,700
Athabasca Oil Corporation [Member]
Property Plant And Equipment [Line Items]
Cost of acquired assets, carried interest						$ 168,000
Cost of acquired assets, interest carry period							5 years
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 (loss) on sale of assets			$ 132,400
Syncrude [Member]
Property Plant And Equipment [Line Items]
Gain (loss) on sale of assets								71,700
Percentage of interest in oil and gas property sold during period						5.00%
Eagle Ford Shale [Member]
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment							$ 19,400
Gain (loss) on sale of assets							0
Montney Natural Gas Fields [Member]
Property Plant And Equipment [Line Items]
Deferred gain on sale of property		185,000				$ 187,000	185,000
Amortization of deferred gain on sale of property							$ 5,300	$ 3,400
Deferred gain, period of recognition							19 years
Murphy Oil Corp [Member] | Syncrude [Member]
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment						739,100
Canadian Subsidiary [Member] | Athabasca Oil Corporation [Member]
Property Plant And Equipment [Line Items]
Cost of acquired assets						$ 375,000
Brunei [Member]
Property Plant And Equipment [Line Items]
Exploratory well costs capitalized more than one year		70,400					$ 70,400
Vietnam [Member]
Property Plant And Equipment [Line Items]
Exploratory well costs capitalized more than one year		43,200					43,200
Malaysia [Member]
Property Plant And Equipment [Line Items]
Exploratory well costs capitalized more than one year		23,200					23,200
Redetermination expense				$ 39,100
Reduction in capital lease obligations		56,700					$ 56,700
Kaybob Duvernay Lands, Alberta [Member]
Property Plant And Equipment [Line Items]
Redetermination expense paid		$ 21,800
Interest in assets acquired						70.00%
Working interest			8.60%						6.70%
Montney Lands, Alberta [Member]
Property Plant And Equipment [Line Items]
Interest in assets acquired						30.00%