Fair value measurements (Details 3) - Fair Value, Inputs, Level 3 - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Fair value measurements
Fair value	$ 2,494	$ 2,445
Residential loan | Fair value of property or collateral
Fair value measurements
Fair value	$ 2,377	$ 2,297
Appraised value, selling cost	7.00%	7.00%
Appraised value, weighted average rate (as a percent)	78.00%	83.00%
Residential loan | Fair value of property or collateral | Minimum
Fair value measurements
Appraised value (as a percent)	39.00%	39.00%
Residential loan | Fair value of property or collateral | Maximum
Fair value measurements
Appraised value (as a percent)	99.00%	99.00%
Home equity line of credit | Fair value of property or collateral
Fair value measurements
Fair value	$ 3	$ 3
Appraised value, selling cost	7.00%	7.00%
Appraised value, weighted average rate (as a percent)	7.00%	7.00%
Commercial loans | Fair value of property or collateral
Fair value measurements
Fair value	$ 114	$ 145
Fair value, weighted average rate (as a percent)	88.00%	91.00%
Real estate acquired in settlement of loans | Fair value of property or collateral
Fair value measurements
Fair value	$ 665	$ 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%