Income taxes - Schedule of Net Deferred Tax liability (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Deferred tax assets:
Allowance for loan losses	$ 7,853	$ 7,539
Operating lease liability	10,090	0
Amortization of core deposit intangible	1,197	1,012
Deferred compensation	4,851	5,878
Unrealized loss on available-for-sale debt securities	100	3,299
Other	2,011	1,998
Subtotal	26,102	19,726
Deferred tax liabilities:
FHLB stock dividends	(550)	(550)
Operating lease - right of use asset	(9,806)	0
Depreciation	(4,615)	(4,812)
Cash flow hedges	(2,252)	(736)
Mortgage servicing rights	(17,296)	(23,146)
Other	(8,474)	(7,145)
Subtotal	(42,993)	(36,389)
Net deferred tax liability	$ (16,891)	$ (16,663)