Goodwill and other intangible assets - Components of other intangible assets subject to amortization (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets
Core deposits - Gross		$ 24,400
Customer relationships - Gross		$ 16,300
Gross Amount	$ 39,954		$ 80,621
Finite Lived Intangible Assets Accumulated Amortization	22,600		58,005
Finite-Lived Intangible Assets, Net	17,354		22,616
Core deposits
Finite-Lived Intangible Assets
Core deposits - Gross	12,810		37,224
Finite Lived Intangible Assets Accumulated Amortization	7,152		29,792
Finite-Lived Intangible Assets, Net	5,658		7,432
Other customer relationship
Finite-Lived Intangible Assets
Customer relationships - Gross	26,656		42,909
Finite Lived Intangible Assets Accumulated Amortization	15,236		28,075
Finite-Lived Intangible Assets, Net	11,420		14,834
Trademarks
Finite-Lived Intangible Assets
Gross Amount	488		488
Finite Lived Intangible Assets Accumulated Amortization	212		138
Finite-Lived Intangible Assets, Net	$ 276		$ 350