Goodwill and other intangible assets - Components of other intangible assets subject to amortization (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets
Core deposits - Gross	$ 24,400
Customer relationships - Gross	16,300
Gross Amount	39,871	$ 80,621
Finite Lived Intangible Assets Accumulated Amortization	21,524	58,005
Finite-Lived Intangible Assets, Net	18,347	22,616
Core deposits
Finite-Lived Intangible Assets
Core deposits - Gross	12,810	37,224
Finite Lived Intangible Assets Accumulated Amortization	6,832	29,792
Finite-Lived Intangible Assets, Net	5,978	7,432
Other customer relationship
Finite-Lived Intangible Assets
Customer relationships - Gross	26,573	42,909
Finite Lived Intangible Assets Accumulated Amortization	14,504	28,075
Finite-Lived Intangible Assets, Net	12,069	14,834
Trademarks
Finite-Lived Intangible Assets
Gross Amount	488	488
Finite Lived Intangible Assets Accumulated Amortization	188	138
Finite-Lived Intangible Assets, Net	$ 300	$ 350