Offsetting Assets and Liabilities (Offsetting Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Derivative Asset [Abstract]
Cash Collateral Received	$ (1,800)	$ (1,500)
Securities borrowed
Securities Borrowed [Abstract]
Gross Amounts of Recognized Assets	25,855	75,274
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	25,855	75,274
Financial Instruments	0	0
Cash Collateral Received	(25,855)	(75,274)
Net Amount	0	0
Derivatives
Derivative Asset [Abstract]
Gross Amounts of Recognized Assets	9,155	12,588
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	9,155	12,588
Financial Instruments	0	0
Cash Collateral Received	(1,788)	(1,518)
Net Amount	7,367	11,070
Exchange-traded options | Long
Derivative Asset [Abstract]
Gross Amounts of Recognized Assets	4,709	5,910
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	4,709	5,910
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	4,709	$ 5,910
Consolidated VIEs
Derivative Asset [Abstract]
Gross Amounts of Recognized Assets	66,227
Gross Amounts Offset in the Statement of Financial Position	0
Net Amounts of Assets Presented in the Statement of Financial Position	66,227
Financial Instruments	0
Cash Collateral Received	(1,460)
Net Amount	$ 64,767