Short-Term Borrowings - Mortgage Loans Sold Under Agreement to Repurchase by Counterparty (Details) - Loan Repo Facility $ in Thousands	Dec. 31, 2021 USD ($)
Credit Suisse First Boston Mortgage Capital LLC Tranche Two
Mortgage loans sold under agreement to repurchase
Amount at risk	$ 2,688,383
Credit Suisse First Boston Mortgage Capital LLC Tranche One
Mortgage loans sold under agreement to repurchase
Amount at risk	137,054
Bank of America, N.A.
Mortgage loans sold under agreement to repurchase
Amount at risk	674,074
JP Morgan Chase Bank
Mortgage loans sold under agreement to repurchase
Amount at risk	355,202
JP Morgan
Mortgage loans sold under agreement to repurchase
Amount at risk	9,914
BNP Paribas
Mortgage loans sold under agreement to repurchase
Amount at risk	17,568
Barclays
Mortgage loans sold under agreement to repurchase
Amount at risk	74,455
Goldman Sachs
Mortgage loans sold under agreement to repurchase
Amount at risk	48,483
Citibank, N.A.
Mortgage loans sold under agreement to repurchase
Amount at risk	20,948
Morgan Stanley Bank, N.A.
Mortgage loans sold under agreement to repurchase
Amount at risk	17,469
Royal Bank of Canada
Mortgage loans sold under agreement to repurchase
Amount at risk	68,643
Wells Fargo Bank, N.A.
Mortgage loans sold under agreement to repurchase
Amount at risk	$ 12,395