Goodwill and intangible assets - Schedule of Core Deposit and Other Intangibles (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 54,853	$ 52,363
Accumulated Amortization	(35,977)	(34,774)
Net Carrying Amount	18,876	17,589
Core deposit intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	52,165	49,675
Accumulated Amortization	(34,970)	(33,861)
Net Carrying Amount	17,195	15,814
Customer base trust intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,600	1,600
Accumulated Amortization	(427)	(387)
Net Carrying Amount	1,173	1,213
Manufactured housing servicing intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,088	1,088
Accumulated Amortization	(580)	(526)
Net Carrying Amount	$ 508	$ 562