Fair value measurements (Details 3) - Fair Value, Inputs, Level 3 - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Fair value measurements
Fair value	$ 951	$ 2,445
Fair value of property or collateral | Residential loan
Fair value measurements
Fair value	$ 823	$ 2,297
Appraised value, selling cost	7.00%	7.00%
Appraised value, weighted average rate (as a percent)	70.00%	83.00%
Fair value of property or collateral | Residential loan | Minimum
Fair value measurements
Appraised value (as a percent)	31.00%	39.00%
Fair value of property or collateral | Residential loan | Maximum
Fair value measurements
Appraised value (as a percent)	91.00%	99.00%
Fair value of property or collateral | Home equity line of credit
Fair value measurements
Fair value	$ 128	$ 3
Appraised value, selling cost	7.00%	7.00%
Appraised value, weighted average rate (as a percent)	52.00%	7.00%
Fair value of property or collateral | Commercial loans
Fair value measurements
Fair value		$ 145
Fair value, weighted average rate (as a percent)		91.00%
Fair value of property or collateral | Real estate acquired in settlement of loans
Fair value measurements
Fair value	$ 70	$ 288
Appraised value, selling cost	7.00%	7.00%
Appraised value (as a percent)	100.00%	100.00%
Appraised value, weighted average rate (as a percent)	100.00%	100.00%