Related party transactions - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Deposits from related parties	$ 281,119		$ 287,156
Aviation Time Sharing Agreement
Related Party Transaction [Line Items]
Payments to related party	27	$ 72
Certain Executive Officers, Certain Management and Directors and Their Associates
Related Party Transaction [Line Items]
Unfunded commitments	18,382		15,000
Director
Related Party Transaction [Line Items]
Unamortized leasehold improvements	111		116
Lease expense	129	$ 148
Amount of investment held by the company	$ 29		$ 29

For investments which are quantified by principal amount, the principle balance held at close of period.

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