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Loans and Allowance for Loan Losses - Percentage of Loans Geographically and by Collateral (Details) | Dec. 31, 2017 | Dec. 31, 2016
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Commercial real estate |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Percentage of loans by class to all loans | 67.00% |
Commercial real estate | California |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Percentage of loans by class and geographic location | 85.00% |
Loans secured by real estate |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Percentage of loans by class to all loans | 87.00% | 85.00%

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