Offsetting Assets and Liabilities (Offsetting Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Derivative Asset [Abstract]
Cash Collateral Received	$ (800)	$ (1,500)
Securities borrowed
Securities Borrowed [Abstract]
Gross Amounts of Recognized Assets	42,761	75,274
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	42,761	75,274
Financial Instruments	0	0
Cash Collateral Received	(42,761)	(75,274)
Net Amount	0	0
Derivatives
Derivative Asset [Abstract]
Gross Amounts of Recognized Assets	6,944	12,588
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	6,944	12,588
Financial Instruments	0	0
Cash Collateral Received	(810)	(1,518)
Net Amount	6,134	11,070
Exchange-traded options | Long
Derivative Asset [Abstract]
Gross Amounts of Recognized Assets	3,549	5,910
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	3,549	5,910
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	3,549	$ 5,910
Consolidated VIEs
Derivative Asset [Abstract]
Gross Amounts of Recognized Assets	3,968
Gross Amounts Offset in the Statement of Financial Position	0
Net Amounts of Assets Presented in the Statement of Financial Position	3,968
Financial Instruments	0
Cash Collateral Received	(393)
Net Amount	$ 3,575