Other real estate owned - Summary of Other Real Estate Owned (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Other Real Estate [Roll Forward]
Balance at beginning of period	$ 17,072	$ 12,828	$ 18,939	$ 12,643
Transfers from loans	641	924	1,006	2,030
Transfers from (to) premises and equipment	0	2,640	(841)	2,640
Proceeds from sale of other real estate owned	(2,708)	(1,148)	(4,150)	(1,864)
Gain on sale of other real estate owned	170	329	345	322
Loans provided for sales of other real estate owned	0	0	0	(166)
Write-downs and partial liquidations	(84)	(52)	(208)	(84)
Balance at end of period	$ 15,091	$ 15,521	$ 15,091	$ 15,521