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	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Federal taxes calculated at statutory rate	$ (1,604)	$ 6,653	$ 4,938	$ 17,272
Federal taxes calculated at statutory rate, percent	21.00%	21.00%	21.00%	21.00%
Increase (decrease) resulting from:
State taxes, net of federal benefit	$ 100	$ 1,512	$ 1,266	$ 3,855
Expense (benefit) from equity based compensation	(7)	(275)	154	(668)
Municipal interest income, net of interest disallowance	(422)	(211)	(996)	(650)
Bank owned life insurance	(55)	(11)	(90)	(38)
Merger costs	126	0	289	0
Other	(177)	50	(65)	236
Total	$ (2,040)	$ 7,718	$ 5,495	$ 20,007
Effective Income Tax Rate Reconciliation, Percent [Abstract]
State taxes, net of federal benefit, percent	(1.30%)	4.70%	5.40%	4.70%
Expense (benefit) from equity based compensation, percent	0.10%	(0.90%)	0.70%	(0.80%)
Municipal interest income, net of interest disallowance, percent	5.50%	(0.70%)	(4.20%)	(0.80%)
Bank owned life insurance, percent	0.70%	0.10%	(0.40%)	0.10%
Merger costs, percent	(1.60%)	0.00%	1.20%	0.00%
Other, percent	2.30%	0.20%	(0.30%)	0.30%
Total, percentage	26.70%	24.40%	23.40%	24.30%

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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