Investment in Securities, Master Netting Arrangements for Swaps (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Offsetting Derivative Assets [Abstract]
Gross amounts of recognized assets	$ 174	$ 896	$ 156
Swaps [Member]
Offsetting Derivative Assets [Abstract]
Gross amounts of recognized assets	174	896	156
Gross amounts offset in the Statements of Financial Position	0	0	0
Net Amounts of Assets Presented in the Statements of Financial Position	174	896	156
Gross Amounts Not Offset in the Statements of Financial Position, Assets [Abstract]
Financial Instruments	(107)	(634)	(156)
Cash collateral received	0	0	0
Net amount	67	262	0
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized liabilities	107	634	205
Gross amounts offset in the Statements of Financial Position	0	0	0
Net Amounts of Assets Presented in the Statements of Financial Position	107	634	205
Gross Amounts Not Offset in the Statements of Financial Position, Liabilities [Abstract]
Financial Instruments	(107)	(634)	(156)
Cash collateral received	0	0	0
Net amount	$ 0	$ 0	$ 49