Offsetting Assets and Liabilities, Offsetting Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivative Liability [Abstract]
Cash Collateral Pledged	$ (11,931)	$ (13,241)
Securities Loaned [Member]
Securities Loaned [Abstract]
Gross Amounts of Recognized Liabilities	2,184	33,645
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	2,184	33,645
Financial Instruments	0	0
Cash Collateral Pledged	(2,184)	(33,645)
Net Amount	0	0
Derivatives [Member]
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	9,773	9,392
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	9,773	9,392
Financial Instruments	0	0
Cash Collateral Pledged	(9,773)	(9,392)
Net Amount	0	0
Exchange Traded Options [Member] | Short [Member]
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	5,602	7,118
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	5,602	7,118
Financial Instruments	0	0
Cash Collateral Pledged	0	0
Net Amount	$ 5,602	$ 7,118