Goodwill and other intangible assets - Components of other intangible assets subject to amortization (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets
Gross Amount	$ 80,621	$ 80,621
Finite Lived Intangible Assets Accumulated Amortization	60,478	58,005
Finite-Lived Intangible Assets, Net	20,143	22,616
Core deposits
Finite-Lived Intangible Assets
Core deposits - Gross	37,224	37,224
Finite Lived Intangible Assets Accumulated Amortization	30,723	29,792
Finite-Lived Intangible Assets, Net	6,501	7,432
Other customer relationship
Finite-Lived Intangible Assets
Customer relationships - Gross	42,909	42,909
Finite Lived Intangible Assets Accumulated Amortization	29,592	28,075
Finite-Lived Intangible Assets, Net	13,317	14,834
Trademarks
Finite-Lived Intangible Assets
Gross Amount	488	488
Finite Lived Intangible Assets Accumulated Amortization	163	138
Finite-Lived Intangible Assets, Net	$ 325	$ 350