Loans and allowance for credit losses - Changes in Value of Accretable Yield for PCI Loans (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Accretion		$ 2,554	$ 3,928
Purchased Credit Impaired
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at the beginning of period	$ (14,814)		(16,587)
Additions through business combinations	(1,167)		(1,167)
Principal reductions and other reclassifications from nonaccretable difference	30		250
Accretion	1,705		3,888
Changes in expected cash flows	(616)		(1,246)
Balance at end of period	$ (14,862)		$ (14,862)