Fair value estimates - Schedule of Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Details) - Nonrecurring Basis - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Impaired loans	$ 2,474	$ 3,193
Other real estate owned	236	371
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Impaired loans	2,474	3,193
Other real estate owned	$ 236	$ 371