Derivative Instruments (Offsetting Assets and Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Derivatives Assets
Gross Amounts of Recognized Financial Instruments	$ 317,165	$ 251,765
Gross Amounts Offset in the Consolidated Statement of Financial Position	(281,406)	(239,220)
Net Amounts Presented in the Consolidated Statement of Financial Position	35,759	12,545
Financial Instruments/Collateral	(34,768)	(12,545)
Net Amount	991	0
Securities Purchased under Agreements to Resell
Gross Amounts of Recognized Financial Instruments	139,384	0
Gross Amounts Offset in the Consolidated Statement of Financial Position	0	0
Net Amounts Presented in the Consolidated Statement of Financial Position	139,384	0
Financial Instruments/Collateral	(139,384)	0
Net Amount	0	0
Total Assets
Gross Amounts of Recognized Financial Instruments	456,549	251,765
Gross Amounts Offset in the Consolidated Statement of Financial Position	(281,406)	(239,220)
Net Amounts Presented in the Consolidated Statement of Financial Position	175,143	12,545
Financial Instruments/Collateral	(174,152)	(12,545)
Net Amount	991	0
Derivatives Liabilities
Gross Amounts of Recognized Financial Instruments	74,351	97,802
Gross Amounts Offset in the Consolidated Statement of Financial Position	(74,351)	(97,802)
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	74,351	97,802
Gross Amounts Offset in the Consolidated Statement of Financial Position	(74,351)	(97,802)
Net Amounts Presented in the Consolidated Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	$ 0	$ 0