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Multifamily Loans - Geographic Concentration of Multifamily Loans (Details) - Multifamily securities - Geographic Concentration Risk - Loan Benchmark | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 100.00% | 100.00%
California |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 13.00% | 13.00%
Florida |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 13.00% | 13.00%
North Carolina |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 9.00% | 9.00%
Oregon |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 7.00% | 7.00%
Hawaii |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 5.00% | 5.00%
Tennessee |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 5.00% | 5.00%
Other states (none greater than 5%) |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 48.00% | 48.00%

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