Offsetting Assets and Liabilities (Offsetting Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Derivative Liability [Abstract]
Cash Collateral Pledged	$ (5,900)	$ (12,800)
Securities loaned
Securities Loaned [Abstract]
Gross Amounts of Recognized Liabilities	13,200	9,518
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	13,200	9,518
Financial Instruments	0	0
Cash Collateral Pledged	(13,200)	(9,518)
Net Amount	0	0
Derivatives
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	9,548	12,221
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	9,548	12,221
Financial Instruments	0	0
Cash Collateral Pledged	(5,905)	(12,221)
Net Amount	3,643	0
Exchange-traded options | Short
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	772	843
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	772	843
Financial Instruments	0	0
Cash Collateral Pledged	0	0
Net Amount	772	$ 843
Consolidated VIEs
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	57,467
Gross Amounts Offset in the Statement of Financial Position	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	57,467
Financial Instruments	0
Cash Collateral Pledged	(9,493)
Net Amount	$ 47,974