Derivative Instruments (Offsetting Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Offsetting of Financial Assets, Derivatives
Gross Amounts of Recognized Financial Instruments	$ 77,887	$ 115,086
Gross Amounts Offset in the Consolidated Statement of Financial Position	(27,078)	(115,086)
Net Amounts Presented in the Consolidated Statement of Financial Position	50,809	0
Financial Instruments/Collateral	(7,307)	0
Net Amount	43,502	0
Securities purchased under agreements to resell
Gross Amounts of Recognized Financial Instruments	143,000	148,000
Gross Amounts Offset in the Consolidated Statement of Financial Position	0	0
Net Amounts Presented in the Consolidated Statement of Financial Position	143,000	148,000
Financial Instruments/Collateral	(143,000)	(148,000)
Net Amount	0	0
Total Assets
Gross Amounts of Recognized Financial Instruments	220,887	263,086
Gross Amounts Offset in the Consolidated Statement of Financial Position	(27,078)	(115,086)
Net Amounts Presented in the Consolidated Statement of Financial Position	193,809	148,000
Financial Instruments/Collateral	(150,307)	(148,000)
Net Amount	43,502	0
Offsetting of Financial Liabilities, Derivatives
Gross Amounts of Recognized Financial Instruments	26,862	74,378
Gross Amounts Offset in the Consolidated Statement of Financial Position	(26,862)	(69,718)
Net Amounts Presented in the Consolidated Statement of Financial Position	0	4,660
Financial Instruments/Collateral	0	(245)
Net Amount	0	4,415
Securities sold under agreements 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	26,862	74,378
Gross Amounts Offset in the Consolidated Statement of Financial Position	(26,862)	(69,718)
Net Amounts Presented in the Consolidated Statement of Financial Position	0	4,660
Financial Instruments/Collateral	0	(245)
Net Amount	$ 0	$ 4,415