Repurchase Agreements Remaining Term to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 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	$ 2,527,065	$ 2,437,163
Assets Sold under Agreements to Repurchase, Interest Rate	0.20%	0.34%
WAVG Original Term to Maturity	165	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	$ 479,019	$ 1,416,608
Assets Sold under Agreements to Repurchase, Interest Rate	0.30%	0.37%
WAVG Original Term to Maturity	110	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	$ 620,085	$ 845,394
Assets Sold under Agreements to Repurchase, Interest Rate	0.12%	0.31%
WAVG Original Term to Maturity	125	35
Maturity90-180DaysMember
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	$ 1,122,552	$ 175,161
Assets Sold under Agreements to Repurchase, Interest Rate	0.22%	0.22%
WAVG Original Term to Maturity	168	13
Maturity 181 days to 1 year
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	$ 305,409
Assets Sold under Agreements to Repurchase, Interest Rate	0.15%
WAVG Original Term to Maturity	318