Derivatives (Offsetting of Derivatives) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Derivative assets
Gross Amounts Recognized	$ 834,204	$ 330,316
Less: Master netting agreements	(158,674)	(121,561)
Less: Cash collateral received/pledged	(20,100)	(3,758)
Derivative asset, after netting	655,430	204,997
Less: Security Collateral Received	(29,103)	0
Net derivative assets	626,327	204,997
Derivative assets subject to master netting arrangements, gross amounts recognized	831,900	328,700
Contracts not subject to master netting arrangements, gross amounts recognized	2,300	1,600
Derivative, cash collateral received, including amount offset by fair value assets, and excess cash amount	20,100	3,800
Amount used to offset against derivative assets	20,100	3,758
Derivative liabilities
Gross Amounts Recognized	658,515	256,528
Less: Master netting agreements	(158,674)	(121,561)
Less: Cash collateral received/pledged	(84,427)	(38,238)
Derivative liability, after netting	415,414	96,729
Less: Security Collateral Pledged	(232,940)	(79,619)
Net derivative liabilities	182,474	17,110
Derivative liability subject to master netting arrangements, gross amounts recognized	657,600	256,528
Contracts not subject to master netting arrangements, gross amounts recognized	931	20
Derivative, cash collateral posted against derivative liabilities, including amount offset the derivative fair value liabilities, and excess cash amount	89,800	43,000
Amount used to offset against derivative liabilities	$ 84,427	$ 38,238