Goodwill and intangible assets - Schedule of Core Deposit and Other Intangibles (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 52,363	$ 42,190
Accumulated Amortization	(34,774)	(30,562)
Net Carrying Amount	17,589	11,628
Core deposit intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	49,675	38,915
Accumulated Amortization	(33,861)	(29,901)
Net Carrying Amount	15,814	9,014
Leasehold intangible(1)
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		587
Accumulated Amortization		(127)
Net Carrying Amount		460
Customer base trust intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,600	1,600
Accumulated Amortization	(387)	(227)
Net Carrying Amount	1,213	1,373
Manufactured housing servicing intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,088	1,088
Accumulated Amortization	(526)	(307)
Net Carrying Amount	$ 562	$ 781