Other assets and other liabilities - Summary of Other Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Other Assets And Other Liabilities [Abstract]
Cash surrender value on bank owned life insurance	$ 11,357	$ 11,115
Prepaid expenses	4,575	3,283
Software	1,999	1,313
Mortgage lending receivable	10,765	3,876
Derivatives	21,981	14,316
FHLB lender risk account receivable	11,225	5,225
Margin Deposit Assets	33,616	13,904
Other assets	27,196	17,070
Total other assets	$ 122,714	$ 70,102