Income taxes - Schedule of Net Deferred Tax liability (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Deferred tax assets:
Allowance for loan losses	$ 8,198	$ 7,539
Operating lease liability	9,839	0
Amortization of core deposit intangible	1,273	1,012
Deferred compensation	5,891	5,878
Unrealized loss on available-for-sale debt securities	115	3,299
Other	2,451	1,998
Subtotal	27,767	19,726
Deferred tax liabilities:
FHLB stock dividends	(550)	(550)
Operating lease - right of use asset	(9,514)	0
Depreciation	(4,466)	(4,812)
Cash flow hedges	(3,418)	(736)
Mortgage servicing rights	(17,342)	(23,146)
Goodwill	(8,244)	(6,583)
Other	(901)	(562)
Subtotal	(44,435)	(36,389)
Net deferred tax liability	$ (16,668)	$ (16,663)