Goodwill and intangible assets - Activity (Details) - USD ($) $ in Thousands			9 Months Ended
	Aug. 15, 2020	Feb. 14, 2020	Sep. 30, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Goodwill, beginning balance			$ 169,051
Goodwill, ending balance			236,086
Finite-lived Intangible Assets [Roll Forward]
Core deposit and other intangibles, beginning balance			17,589
Accumulated Amortization			(38,599)	$ (34,774)
Core deposit and other intangibles, ending balance			23,924
Core deposit and other intangibles
Finite-lived Intangible Assets [Roll Forward]
Core deposit and other intangibles, beginning balance			17,589
Accumulated Amortization			(3,825)
Core deposit and other intangibles, ending balance			23,924
Farmers National
Goodwill [Roll Forward]
Addition from acquisition/merger		$ 6,390	6,390
Farmers National | Core deposit and other intangibles
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets acquired			2,490
Franklin
Goodwill [Roll Forward]
Addition from acquisition/merger	$ 60,645		60,645
Franklin | Core deposit and other intangibles
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets acquired			$ 7,670