Income taxes - Schedule of Reconciliation of Income Taxes Computed at the United States Federal Statutory Tax Rates to the Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Federal taxes calculated at statutory rate	$ 173	$ 5,368
Federal taxes calculated at statutory rate, percent	21.00%	21.00%
Increase (decrease) resulting from:
State taxes, net of federal benefit	$ (132)	$ 1,138
Benefit of equity based compensation	139	(392)
Municipal interest income, net of interest disallowance	(264)	(216)
Bank owned life insurance	(18)	(12)
Stock offering costs	131	0
Other	51	89
Total	$ 80	$ 5,975
Effective Income Tax Rate Reconciliation, Percent [Abstract]
State taxes, net of federal benefit, percent	(16.00%)	4.50%
Benefit of equity based compensation, percent	16.80%	(1.50%)
Municipal interest income, net of interest disallowance, percent	(32.00%)	(0.80%)
Bank owned life insurance, percent	(2.20%)	(0.00%)
Stock offering costs, percent	15.90%	0.00%
Other, percent	6.20%	0.20%
Income tax expense, as reported	9.70%	23.40%

Effective income tax rate reconciliation, municipal interest income net of interest disallowance, percent.

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Effective income tax rate reconciliation nondeductible expense merger costs.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to life insurance expense.

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