Shareholders' equity and regulatory matters (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Mar. 27, 2015
Total capital (to risk-weighted assets), Amount [Abstract]
For Capital Adequacy Purposes		$ 13,707
To be Well Capitalized Amount		$ 15,231
Total capital (to risk-weighted assets), Ratio [Abstract]
Actual Ratio (in percentage)		12.85%
To be Well Capitalized (in percentage)		6.50%
Leverage ratio (Tier 1 capital to average assets), Amount [Abstract]
To be Well Capitalized Amount		$ 20,970
Leverage ratio (Tier 1 capital to average assets), Ratio [Abstract]
For Capital Adequacy Purposes (in percentage)	4.00%		9.33%
To be Well Capitalized (in percentage)		5.00%
Common equity (Tier 1 risk based capital to risk weighted assets), Ratio [Abstract]
Actual Ratio (in percentage)	31.00%
For Capital Adequacy Purposes (in percentage)	7.00%
Subsidiaries [Member]
Total capital (to risk-weighted assets), Amount [Abstract]
Actual Amount	$ 49,225	$ 42,695
For Capital Adequacy Purposes	25,693	24,369
To be Well Capitalized Amount	$ 42,117	$ 30,461
Total capital (to risk-weighted assets), Ratio [Abstract]
Actual Ratio (in percentage)	15.33%	14.02%
For Capital Adequacy Purposes (in percentage)	8.00%	8.00%
To be Well Capitalized (in percentage)	10.00%	10.00%
Tier 1 capital (to risk-capital to average assets), Amount [Abstract]
Actual Amount	$ 45,852	$ 39,133
For Capital Adequacy Purposes	12,847	12,184
To be Well Capitalized Amount	$ 19,270	$ 18,277
Tier 1 capital (to risk-capital to average assets), Ratio [Abstract]
Actual Ratio (in percentage)	14.28%	12.85%
For Capital Adequacy Purposes (in percentage)	4.00%	4.00%
To be Well Capitalized (in percentage)	6.00%	6.00%
Leverage ratio (Tier 1 capital to average assets), Amount [Abstract]
Actual Amount	$ 45,852	$ 39,133
For Capital Adequacy Purposes	17,523	$ 16,776
To be Well Capitalized Amount	$ 21,903
Leverage ratio (Tier 1 capital to average assets), Ratio [Abstract]
Actual Ratio (in percentage)	10.47%	9.33%
For Capital Adequacy Purposes (in percentage)	4.00%	4.00%
To be Well Capitalized (in percentage)	5.00%
Common equity (Tier 1 risk based capital to risk weighted assets), Amount [Abstract]
Actual Amount	$ 45,852	$ 39,133
For Capital Adequacy Purposes	14,452
To be Well Capitalized Amount	$ 20,876
Common equity (Tier 1 risk based capital to risk weighted assets), Ratio [Abstract]
Actual Ratio (in percentage)	14.28%
For Capital Adequacy Purposes (in percentage)	4.50%	4.50%
To be Well Capitalized (in percentage)	6.50%