Offsetting Assets and Liabilities (Offsetting Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Derivative Liability [Abstract]
Cash Collateral Pledged	$ (3,500)	$ (13,200)
Securities loaned
Securities Loaned [Abstract]
Gross Amounts of Recognized Liabilities	4,751	33,645
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	4,751	33,645
Financial Instruments	0	0
Cash Collateral Pledged	(4,751)	(33,645)
Net Amount	0	0
Derivatives
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	11,354	9,392
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	11,354	9,392
Financial Instruments	0	0
Cash Collateral Pledged	(3,545)	(9,392)
Net Amount	7,809	0
Exchange-traded options | Short
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	4,103	7,118
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	4,103	7,118
Financial Instruments	0	0
Cash Collateral Pledged	0	0
Net Amount	$ 4,103	$ 7,118