Derivative Instruments - Gain From Derivative Instruments (Details) - Not designated as hedging instruments - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Gain impact of derivative instruments not designated as hedging instruments
Gain impact that derivative instruments not designated as hedging instruments had on results of operations	$ 1,162,272	$ (112,018)	$ 191,909
Futures
Gain impact of derivative instruments not designated as hedging instruments
Gain impact that derivative instruments not designated as hedging instruments had on results of operations	1,180,483	(78,234)	191,046
Currency forwards
Gain impact of derivative instruments not designated as hedging instruments
Gain impact that derivative instruments not designated as hedging instruments had on results of operations	(16,431)	(32,785)	(1,817)
Options
Gain impact of derivative instruments not designated as hedging instruments
Gain impact that derivative instruments not designated as hedging instruments had on results of operations	(1,784)	(987)	$ 2,680
Interest rate swaps
Gain impact of derivative instruments not designated as hedging instruments
Gain impact that derivative instruments not designated as hedging instruments had on results of operations	$ 4	$ (12)