Derivative Financial Instruments (Settlement) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) item	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Derivatives
Gain on derivative instruments	$ 33,897	$ 121,669	$ 814
Amount received on settlements of derivatives	92,000		46,200
Amount paid on settlements of derivatives		10,800
Other income (expenses)
Derivatives
Gain on derivative instruments	$ 33,897	$ 121,669	$ 814
Not designated
Derivatives
Number of derivative contracts | item	0