Offsetting Assets and Liabilities - Offsetting Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Derivative Liability [Abstract]
Collateral Pledged	$ (6,200)	$ (12,800)
Consolidated VIEs [Member]
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	2,081
Gross Amounts Offset in the Statement of Financial Position	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	2,081
Financial Instruments	0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	(2,081)
Collateral Pledged	(3,311)
Net Amount	0
Securities Loaned [Member]
Securities Loaned [Abstract]
Gross Amounts of Recognized Liabilities	0	9,518
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	0	9,518
Financial Instruments	0	0
Collateral Pledged	0	(9,518)
Net Amount	0	0
Derivatives [Member]
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	8,649	12,221
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	8,649	12,221
Financial Instruments	0	0
Collateral Pledged	(6,239)	(12,221)
Net Amount	2,410	0
Exchange Traded Options [Member] | Short [Member]
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	692	843
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	692	843
Financial Instruments	0	0
Collateral Pledged	0	0
Net Amount	$ 692	$ 843