Fair value measurements - Summary of Level 3 financial instruments (Details) - Level 3 - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Fair value measurements
Fair value	$ 224	$ 77
Fair value of property or collateral | Home equity line of credit
Fair value measurements
Fair value	$ 199	$ 77
Appraised value, selling cost	7.00%	7.00%
Fair value of property or collateral | Residential land
Fair value measurements
Fair value	$ 25
Appraised value, selling cost	7.00%
Fair value of property or collateral | Real estate acquired in settlement of loans
Fair value measurements
Fair value		$ 186
Appraised value, selling cost		7.00%