Fair value measurements - Quantitative Information About Level 3 Fair Value Measurements (Details) - Level 3 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Loans
Fair value measurements
Fair value	$ 25	$ 77
Home equity line of credit | Fair value of property or collateral
Fair value measurements
Fair value	$ 77
Selling cost	7.00%
Residential loan | Fair value of property or collateral
Fair value measurements
Fair value	$ 25
Selling cost		7.00%
Real estate acquired in settlement of loans
Fair value measurements
Fair value		$ 186
Real estate acquired in settlement of loans | Fair value of property or collateral
Fair value measurements
Selling cost	7.00%