Significant Accounting Policies (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2014		Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Significant Accounting Policies [Line Items]
Maturity of Canadian government securities			90 days	90 days
Canadian government securities with maturities greater than 90 days at the date of acquisition	$ 461,313,000	[1]	$ 173,288,000	$ 461,313,000	[1]
Impairment of assets			$ 2,493,156,000	51,314,000		$ 21,587,000
Goodwill	0			$ 0
Stock Options [Member]
Significant Accounting Policies [Line Items]
Stock-based compensation, fair value assumption model			Black-Scholes option pricing model
Performance Based Restricted Stock [Member]
Significant Accounting Policies [Line Items]
Stock-based compensation, fair value assumption model			Monte Carlo valuation model
Stock-based compensation, vesting period			3 years
Minimum [Member]
Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage			20.00%
Maturity of Canadian government securities				90 days
Minimum [Member] | Stock Options [Member]
Significant Accounting Policies [Line Items]
Stock-based compensation, vesting period			2 years
Maximum [Member]
Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage			50.00%
Maximum [Member] | Stock Options [Member]
Significant Accounting Policies [Line Items]
Stock-based compensation, vesting period			3 years
Natural Gas Processing Facilities [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Depreciable lives, straight-line method			20 years
Natural Gas Processing Facilities [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Depreciable lives, straight-line method			25 years
Syncrude [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Turnarounds for major processing units			2 years
Syncrude [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Turnarounds for major processing units			3 years
Canada [Member]
Significant Accounting Policies [Line Items]
Impairment of assets	$ 37,047,000

[1] Reclassified to conform to current presentation.