Offsetting Assets and Liabilities (Offsetting Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Derivative Liability [Abstract]
Cash Collateral Pledged	$ (5,100)	$ (12,800)
Securities loaned
Securities Loaned [Abstract]
Gross Amounts of Recognized Liabilities	4,690	9,518
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	4,690	9,518
Financial Instruments	0	0
Cash Collateral Pledged	(4,690)	(9,518)
Net Amount	0	0
Derivatives
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	7,050	12,221
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	7,050	12,221
Financial Instruments	0	0
Cash Collateral Pledged	(5,092)	(12,221)
Net Amount	1,958	0
Exchange-traded options | Short
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	4,321	843
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	4,321	843
Financial Instruments	0	0
Cash Collateral Pledged	0	0
Net Amount	4,321	$ 843
Consolidated VIEs
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	4,238
Gross Amounts Offset in the Statement of Financial Position	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	4,238
Financial Instruments	0
Cash Collateral Pledged	(3,016)
Net Amount	$ 1,222