Mergers and acquisitions - FNB Financial Corp. - Narrative (Details) - FNB Financial Corp. $ / shares in Units, $ in Thousands		12 Months Ended
	Feb. 14, 2020 USD ($) branch $ / shares shares	Dec. 31, 2020 USD ($)
Business Acquisition [Line Items]
Assets assumed in acquisition	$ 258,218
Loans assumed in acquisition	182,171
Deposits assumed in acquisition	$ 209,535
Business acquisition, shares issued (in shares) | shares	954,797
Cash consideration paid	$ 15,001
Business acquisition, share price (in dollars per share) | $ / shares	$ 36.70
Purchase price	$ 50,042
Goodwill resulting from merger	$ 6,319	$ 6,319
Kentucky
Business Acquisition [Line Items]
Number of branches acquired | branch	4