Repurchase Agreements Remaining Term to Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 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	$ 3,314,991	$ 4,752,348
Assets Sold under Agreements to Repurchase, Interest Rate	0.38%	2.01%
WAVG Original Term to Maturity	29	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	$ 1,875,520	$ 2,078,185
Assets Sold under Agreements to Repurchase, Interest Rate	0.40%	2.12%
WAVG Original Term to Maturity	26	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	$ 1,439,471	$ 2,674,163
Assets Sold under Agreements to Repurchase, Interest Rate	0.35%	1.93%
WAVG Original Term to Maturity	32	52