Derivative Instruments (Offsetting Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Offsetting of Financial Assets, Derivatives
Gross Amounts of Recognized Financial Instruments	$ 300,655	$ 243,118
Securities purchased under agreement to resell
Gross Amounts of Recognized Financial Instruments	156,064	93,633
Gross Amounts Offset in the Consolidated Statement of Financial Position	0	0
Net Amounts Presented in the Consolidated Statement of Financial Position	156,064	93,633
Financial Instruments/Collateral	(156,064)	(93,633)
Net Amount	0	0
Total Assets
Gross Amounts of Recognized Financial Instruments	453,435	336,156
Gross Amounts Offset in the Consolidated Statement of Financial Position	(230,554)	(215,066)
Net Amounts Presented in the Consolidated Statement of Financial Position	222,881	121,090
Financial Instruments/Collateral	(171,221)	(100,827)
Net Amount	51,660	20,263
Offsetting of Financial Liabilities, Derivatives
Gross Amounts of Recognized Financial Instruments	32,849	58,687
Securities sold under agreement to repurchase
Gross Amounts of Recognized Financial Instruments	0	0
Gross Amounts Offset in the Consolidated Statement of Financial Position	0	0
Net Amounts Presented in the Consolidated Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	0	0
Total Liabilities
Gross Amounts of Recognized Financial Instruments	32,849	58,687
Gross Amounts Offset in the Consolidated Statement of Financial Position	(32,849)	(58,687)
Net Amounts Presented in the Consolidated Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	0	0
Counterparty
Offsetting of Financial Assets, Derivatives
Gross Amounts of Recognized Financial Instruments	297,371	242,523
Gross Amounts Offset in the Consolidated Statement of Financial Position	(230,554)	(215,066)
Net Amounts Presented in the Consolidated Statement of Financial Position	66,817	27,457
Financial Instruments/Collateral	(15,157)	(7,194)
Net Amount	51,660	20,263
Offsetting of Financial Liabilities, Derivatives
Gross Amounts of Recognized Financial Instruments	32,849	58,687
Gross Amounts Offset in the Consolidated Statement of Financial Position	(32,849)	(58,687)
Net Amounts Presented in the Consolidated Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	$ 0	$ 0