Loans - Analysis of the age of the loan delinquencies by type and by amount past due (Details 2) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 598	$ 136
Current	253,699	226,933
Loans	254,297	227,069
30-59 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	495	136
60-89 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
90 Days and Over
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	103	0
Real estate loans:
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	532	89
Current	250,494	224,958
Loans	251,026	225,047
Real estate loans: | 30-59 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	495	89
Real estate loans: | 60-89 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | 90 Days and Over
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	37	0
Real estate loans: | Secured by one-to-four family residences
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	532	89
Current	201,179	188,484
Loans	201,711	188,573
Real estate loans: | Secured by one-to-four family residences | 30-59 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	495	89
Real estate loans: | Secured by one-to-four family residences | 60-89 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Secured by one-to-four family residences | 90 Days and Over
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	37	0
Real estate loans: | Secured by multi-family residences
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	8,602	5,103
Loans	8,602	5,103
Real estate loans: | Secured by multi-family residences | 30-59 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Secured by multi-family residences | 60-89 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Secured by multi-family residences | 90 Days and Over
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	10,295	6,134
Loans	10,295	6,134
Real estate loans: | Construction | 30-59 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Construction | 60-89 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Construction | 90 Days and Over
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	12,728	8,440
Loans	12,728	8,440
Real estate loans: | Commercial | 30-59 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Commercial | 60-89 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Commercial | 90 Days and Over
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	17,690	16,797
Loans	17,690	16,797
Real estate loans: | Home equity lines of credit | 30-59 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Home equity lines of credit | 60-89 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate loans: | Home equity lines of credit | 90 Days and Over
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Other Loans Portfolio Segment | Commercial & industrial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	66	47
Current	3,137	1,900
Loans	3,203	1,947
Other Loans Portfolio Segment | Commercial & industrial loans | 30-59 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	47
Other Loans Portfolio Segment | Commercial & industrial loans | 60-89 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Other Loans Portfolio Segment | Commercial & industrial loans | 90 Days and Over
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	66	0
Other Loans Portfolio Segment | Other loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	68	75
Loans	68	75
Other Loans Portfolio Segment | Other loans | 30-59 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Other Loans Portfolio Segment | Other loans | 60-89 Days Past Due And Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Other Loans Portfolio Segment | Other loans | 90 Days and Over
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0	$ 0