Derivative Instruments (Offsetting Assets and Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivatives Assets
Gross Amounts of Recognized Financial Instruments	$ 334,977	$ 251,765
Gross Amounts Offset in the Consolidated Statement of Financial Position	(309,388)	(239,220)
Net Amounts Presented in the Consolidated Statement of Financial Position	25,589	12,545
Financial Instruments/Collateral	(25,589)	(12,545)
Net Amount	0	0
Securities Purchased under Agreements to Resell
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 Assets
Gross Amounts of Recognized Financial Instruments	334,977	251,765
Gross Amounts Offset in the Consolidated Statement of Financial Position	(309,388)	(239,220)
Net Amounts Presented in the Consolidated Statement of Financial Position	25,589	12,545
Financial Instruments/Collateral	(25,589)	(12,545)
Net Amount	0	0
Derivatives Liabilities
Gross Amounts of Recognized Financial Instruments	130,443	97,802
Gross Amounts Offset in the Consolidated Statement of Financial Position	(130,443)	(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	130,443	97,802
Gross Amounts Offset in the Consolidated Statement of Financial Position	(130,443)	(97,802)
Net Amounts Presented in the Consolidated Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	$ 0	$ 0