Offsetting Assets and Liabilities (Offsetting Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Derivative Liability [Abstract]
Cash Collateral Pledged	$ (6,400)	$ (13,200)
Securities Loaned [Member]
Securities Loaned [Abstract]
Gross Amounts of Recognized Liabilities	6,900	33,645
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	6,900	33,645
Financial Instruments	0	0
Cash Collateral Pledged	(6,900)	(33,645)
Net Amount	0	0
Derivatives [Member]
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	10,615	9,392
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	10,615	9,392
Financial Instruments	0	0
Cash Collateral Pledged	(6,353)	(9,392)
Net Amount	4,262	0
Exchange Traded Options [Member] | Short [Member]
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	1,907	7,118
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	1,907	7,118
Financial Instruments	0	0
Cash Collateral Pledged	0	0
Net Amount	$ 1,907	$ 7,118