Fair value measurements (Details 3) (Fair Value, Inputs, Level 3, USD $) In Thousands, unless otherwise specified	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%