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Multifamily Loans - Geographic Concentration of Multifamily Loans (Details) - Multifamily loans | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 100.00% | 100.00%
Texas |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 13.00% | 9.00%
California |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 11.00% | 11.00%
Florida |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 10.00% | 0.00%
Arizona |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 6.00% | 8.00%
Georgia |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 6.00% | 6.00%
Washington |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 5.00% | 0.00%
Colorado |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 5.00% | 0.00%
Other states (none greater than 5%) |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Concentration risk percentage | 44.00% | 66.00%

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