Subsequent Events (Details) $ in Thousands, CAD in Millions			3 Months Ended	12 Months Ended
	Jun. 01, 2016 USD ($)	Feb. 15, 2016	Mar. 31, 2016 CAD	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Subsequent Event [Line Items]
Proceeds from sales of property, plant and equipment | $				$ 423,911	$ 1,467,046	$ 1,650
Cost of acquired assets | $				12,600	$ 100,300	$ 48,800
Scenario, Forecast [Member]
Subsequent Event [Line Items]
Cost of acquired assets | CAD			CAD 475
Cost of acquired assets, cash paid | CAD			250
Cost of acquired assets, carried interest | CAD			CAD 225
Cost of acquired assets, interest carry period			5 years
Scenario, Forecast [Member] | Kaybob Duvernay Lands, Alberta [Member]
Subsequent Event [Line Items]
Interest in assets acquired			70.00%
Scenario, Forecast [Member] | Montney Lands, Alberta [Member]
Subsequent Event [Line Items]
Interest in assets acquired			30.00%
Subsidiary [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Proceeds from sales of property, plant and equipment | CAD			CAD 538
Committed Credit Facility [Member]
Subsequent Event [Line Items]
Credit facility maximum borrowing capacity | $				$ 2,000,000
Credit facility, maturity date				May 01, 2017
Committed Credit Facility [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Interest rate increase	1.00%
Committed Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Credit facility interest rate above LIBOR		1.45%
Committed Credit Facility [Member] | Subsequent Event [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Outstanding notes subject to interest rate increase | $	$ 1,500,000
Interest rate increase	1.00%