Loans and allowance for credit losses - Deferrals Program (Details) $ in Thousands	Jun. 30, 2020 USD ($)
Financing Receivable, Troubled Debt Restructuring [Line Items]
Outstanding loans balance	$ 918,258
Percentage of loans held for investment	19.00%
Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Outstanding loans balance	$ 164,804
Percentage of loans held for investment	12.80%
Residential real estate: | 1-to-4 family mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Outstanding loans balance	$ 83,590
Percentage of loans held for investment	11.30%
Residential real estate: | Residential line of credit
Financing Receivable, Troubled Debt Restructuring [Line Items]
Outstanding loans balance	$ 14,200
Percentage of loans held for investment	6.00%
Residential real estate: | Multi-family mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Outstanding loans balance	$ 45,321
Percentage of loans held for investment	39.40%
Construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Outstanding loans balance	$ 82,514
Percentage of loans held for investment	14.90%
Commercial real estate: | Owner occupied
Financing Receivable, Troubled Debt Restructuring [Line Items]
Outstanding loans balance	$ 190,044
Percentage of loans held for investment	27.80%
Commercial real estate: | Non-owner occupied
Financing Receivable, Troubled Debt Restructuring [Line Items]
Outstanding loans balance	$ 321,707
Percentage of loans held for investment	34.80%
Consumer and other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Outstanding loans balance	$ 16,078
Percentage of loans held for investment	5.70%