Goodwill and intangible assets - Schedule of Core Deposit and Other Intangibles (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Finite-lived Intangible Assets [Roll Forward]
Beginning Balance			$ 11,628
Amortization of intangibles	$ (1,254)	$ (802)	(1,983)	$ (1,655)
Ending Balance	19,945		19,945
Core Deposit and Other Intangibles
Finite-lived Intangible Assets [Roll Forward]
Beginning Balance	10,439	14,027	11,628	14,902
Finite-lived intangible assets acquired	10,760	0	10,760	0
Reclassification of leasehold intangible	0	0	(460)	0
Amortization of intangibles	(1,254)	(824)	(1,983)	(1,699)
Ending Balance	19,945	$ 13,203	19,945	$ 13,203
Lease Agreements | Occupancy and equipment expense
Finite-lived Intangible Assets [Roll Forward]
Amortization of intangibles	$ (22)		$ (44)