Derivative Instruments (Offsetting Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Offsetting of Financial Assets, Derivatives
Gross Amounts of Recognized Financial Instruments	$ 251,765	$ 77,887
Gross Amounts Offset in the Consolidated Statement of Financial Position	(239,220)	(27,078)
Net Amounts Presented in the Consolidated Statement of Financial Position	12,545	50,809
Financial Instruments/Collateral	(12,545)	(7,307)
Net Amount	0	43,502
Securities purchased under agreements to resell
Gross Amounts of Recognized Financial Instruments	0	143,000
Gross Amounts Offset in the Consolidated Statement of Financial Position	0	0
Net Amounts Presented in the Consolidated Statement of Financial Position	0	143,000
Financial Instruments/Collateral	0	(143,000)
Net Amount	0	0
Total Assets
Gross Amounts of Recognized Financial Instruments	251,765	220,887
Gross Amounts Offset in the Consolidated Statement of Financial Position	(239,220)	(27,078)
Net Amounts Presented in the Consolidated Statement of Financial Position	12,545	193,809
Financial Instruments/Collateral	(12,545)	(150,307)
Net Amount	0	43,502
Offsetting of Financial Liabilities, Derivatives
Gross Amounts of Recognized Financial Instruments	97,802	26,862
Gross Amounts Offset in the Consolidated Statement of Financial Position	(97,802)	(26,862)
Net Amounts Presented in the Consolidated Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	0	0
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	97,802	26,862
Gross Amounts Offset in the Consolidated Statement of Financial Position	(97,802)	(26,862)
Net Amounts Presented in the Consolidated Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	$ 0	$ 0