Goodwill and intangible assets - Schedule of Core Deposit and Other Intangibles (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 62,523	$ 52,363
Accumulated Amortization	(38,599)	(34,774)
Net Carrying Amount	23,924	17,589
Core deposit intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	59,835	49,675
Accumulated Amortization	(37,403)	(33,861)
Net Carrying Amount	22,432	15,814
Customer base trust intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,600	1,600
Accumulated Amortization	(507)	(387)
Net Carrying Amount	1,093	1,213
Manufactured housing servicing intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,088	1,088
Accumulated Amortization	(689)	(526)
Net Carrying Amount	$ 399	$ 562