Offsetting Assets and Liabilities - Offsetting Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Offsetting Assets [Line Items]
Derivative, Collateral, Obligation to Return Cash	$ (1,500)	$ (1,000)
Securities Borrowed [Member]
Offsetting Assets [Line Items]
Securities Borrowed, Gross	75,274	158,147
Securities Borrowed, Liability	0	0
Securities Borrowed	75,274	158,147
Securities Borrowed, Collateral, Obligation to Return Securities	0	0
Securities Borrowed. Collateral, Obligation to Return Cash	(75,274)	(158,147)
Securities Borrowed, Amount Offset Against Collateral	0	0
Derivatives [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	12,588	6,787
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Asset	12,588	6,787
Derivative, Collateral, Obligation to Return Securities	0	0
Derivative, Collateral, Obligation to Return Cash	(1,518)	(990)
Derivative Asset, Fair Value, Amount Offset Against Collateral	11,070	5,797
Exchange Traded [Member] | Long [Member] | Exchange Traded Options [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	5,910	22,290
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Asset	5,910	22,290
Derivative, Collateral, Obligation to Return Securities	0	0
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	$ 5,910	$ 22,290