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Loans and Allowance for Loan Losses - Percentage of Loans Geographically and by Collateral (Details)	Dec. 31, 2018	Dec. 31, 2017
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans by class to all loans	67.00%	67.00%
Commercial real estate | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans by class and geographic location	85.00%	85.00%
Loans secured by real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans by class to all loans	88.00%	87.00%

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