Derivative Instruments (Offsetting Assets and Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Derivatives
Gross Amounts of Recognized Financial Instruments	$ 226,570	$ 243,118
Securities purchased under agreement to resell
Gross Amounts of Recognized Financial Instruments	103,223	93,633
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts Presented in the Statement of Financial Position	103,223	93,633
Financial Instruments/Collateral	(103,223)	(93,633)
Net Amount	0	0
Total Assets
Gross Amounts of Recognized Financial Instruments	328,961	336,156
Gross Amounts Offset in the Statement of Financial Position	(177,054)	(215,066)
Net Amounts Presented in the Statement of Financial Position	151,907	121,090
Financial Instruments/Collateral	(112,884)	(100,827)
Net Amount	39,023	20,263
Derivatives
Gross Amounts of Recognized Financial Instruments	71,526	58,687
Securities sold under agreement to repurchase
Gross Amounts of Recognized Financial Instruments	0	0
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts Presented in the Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	0	0
Total Liabilities
Gross Amounts of Recognized Financial Instruments	71,526	58,687
Gross Amounts Offset in the Statement of Financial Position	(71,526)	(58,687)
Net Amounts Presented in the Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	0	0
Counterparty
Derivatives
Gross Amounts of Recognized Financial Instruments	225,738	242,523
Gross Amounts Offset in the Statement of Financial Position	(177,054)	(215,066)
Net Amounts Presented in the Statement of Financial Position	48,684	27,457
Financial Instruments/Collateral	(9,661)	(7,194)
Net Amount	39,023	20,263
Derivatives
Gross Amounts of Recognized Financial Instruments	71,526	58,687
Gross Amounts Offset in the Statement of Financial Position	(71,526)	(58,687)
Net Amounts Presented in the Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	$ 0	$ 0