Offsetting Assets and Liabilities (Offsetting Assets) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Derivative Asset [Abstract]
Cash Collateral Received	$ (1,800)	$ (1,000)
Securities Borrowed [Member]
Securities Borrowed [Abstract]
Gross Amounts of Recognized Assets	92,500	158,147
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	92,500	158,147
Financial Instruments	0	0
Cash Collateral Received	(92,500)	(158,147)
Net Amount	0	0
Derivatives [Member]
Derivative Asset [Abstract]
Gross Amounts of Recognized Assets	14,569	6,787
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	14,569	6,787
Financial Instruments	0	0
Cash Collateral Received	(1,828)	(990)
Net Amount	12,741	5,797
Exchange Traded Options [Member] | Long [Member]
Derivative Asset [Abstract]
Gross Amounts of Recognized Assets	7,935	22,290
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	7,935	22,290
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	$ 7,935	$ 22,290