Repurchase Agreements Remaining Term to Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	$ 2,032,089	$ 2,437,163
Assets Sold under Agreements to Repurchase, Interest Rate	0.26%	0.34%
WAVG Original Term to Maturity	30	44
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	$ 1,119,808	$ 1,416,608
Assets Sold under Agreements to Repurchase, Interest Rate	0.27%	0.37%
WAVG Original Term to Maturity	24	53
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	$ 753,223	$ 845,394
Assets Sold under Agreements to Repurchase, Interest Rate	0.28%	0.31%
WAVG Original Term to Maturity	42	35
Maturity Greater than 90 Days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	$ 159,058	$ 175,161
Assets Sold under Agreements to Repurchase, Interest Rate	0.17%	0.22%
WAVG Original Term to Maturity	14	13