Income taxes - 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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Federal taxes calculated at statutory rate, amount	$ 11,916	$ 6,369	$ 26,293	$ 6,542
Amount increase (decrease) resulting from:
State taxes, net of federal benefit	1,879	1,298	3,629	1,166
(Benefit) expense from equity based compensation	(124)	22	(345)	161
Municipal interest income, net of interest disallowance	(419)	(310)	(843)	(574)
Bank owned life insurance	(82)	(17)	(166)	(35)
Merger and offering costs	127	32	127	163
Section 162(m) limitation	21	0	248	0
Other	122	61	85	112
Total	$ 13,440	$ 7,455	$ 29,028	$ 7,535
Federal taxes calculated at statutory rate, percent	21.00%	21.00%	21.00%	21.00%
Percentage increase (decrease) resulting from:
State taxes, net of federal benefit	3.30%	4.30%	2.90%	3.70%
(Benefit) expense from equity based compensation	(0.20%)	0.10%	(0.30%)	0.50%
Municipal interest income, net of interest disallowance	(0.70%)	(1.00%)	(0.70%)	(1.80%)
Bank owned life insurance	(0.10%)	(0.10%)	(0.10%)	(0.10%)
Merger and offering costs	0.20%	0.10%	0.10%	0.50%
Section 162(m) limitation	0	0	0.002	0
Other	0.20%	0.20%	0.10%	0.40%
Total	23.70%	24.60%	23.20%	24.20%