Goodwill and other intangible assets - Components of other intangible assets subject to amortization (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets
Gross Amount	$ 74,356	$ 72,627
Finite Lived Intangible Assets Accumulated Amortization	59,040	51,958
Finite-Lived Intangible Assets, Net	15,316	20,669
Core deposits
Finite-Lived Intangible Assets
Core deposits - Gross	37,224	37,224
Finite Lived Intangible Assets Accumulated Amortization	28,861	26,070
Finite-Lived Intangible Assets, Net	8,363	11,154
Other customer relationship
Finite-Lived Intangible Assets
Customer relationships - Gross	36,644	34,915
Finite Lived Intangible Assets Accumulated Amortization	30,065	25,847
Finite-Lived Intangible Assets, Net	6,579	9,068
Trademarks
Finite-Lived Intangible Assets
Gross Amount	488	488
Finite Lived Intangible Assets Accumulated Amortization	114	41
Finite-Lived Intangible Assets, Net	$ 374	$ 447