Repurchase Agreements Remaining Term to Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	$ 4,408,106	$ 4,752,348
Assets Sold under Agreements to Repurchase, Interest Rate	1.71%	2.01%
WAVG Original Term to Maturity	56	45
Less than 30 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	$ 4,203,459	$ 2,078,185
Assets Sold under Agreements to Repurchase, Interest Rate	1.70%	2.12%
WAVG Original Term to Maturity	54	34
30 to 90 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	$ 204,647	$ 2,674,163
Assets Sold under Agreements to Repurchase, Interest Rate	1.80%	1.93%
WAVG Original Term to Maturity	93	52