Income taxes - Schedule of Net Deferred Tax liability (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Allowance for loan losses	$ 8,113	$ 7,539
Operating lease liability	9,373	0
Amortization of core deposit intangible	1,386	1,012
Deferred compensation	5,231	5,878
Unrealized loss on debt securities	54	3,278
Unrealized loss on equity securities	60	21
Other	2,388	1,998
Subtotal	26,605	19,726
Deferred tax liabilities:
FHLB stock dividends	(550)	(550)
Operating lease - right of use asset	(8,641)	0
Depreciation	(5,078)	(4,812)
Unrealized gain on cash flow hedges	(203)	(736)
Unrealized gain on debt securities	(3,051)	0
Mortgage servicing rights	(19,678)	(23,146)
Goodwill	(8,859)	(6,583)
Other	(1,035)	(562)
Subtotal	(47,095)	(36,389)
Net deferred tax liability	$ (20,490)	$ (16,663)