Loans - Risk category of loans by class (Details 1) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 272,016	$ 263,973
Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	268,202	260,664
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	992	116
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,822	3,193
Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Commercial & industrial loans | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	267,701	260,224
Real estate loans | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	263,932	256,915
Real estate loans | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	116
Real estate loans | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,822	3,193
Real estate loans | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans | Secured by one-to-four family residences
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	217,157	206,894
Real estate loans | Secured by one-to-four family residences | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	214,547	203,815
Real estate loans | Secured by one-to-four family residences | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	116
Real estate loans | Secured by one-to-four family residences | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,610	2,963
Real estate loans | Secured by one-to-four family residences | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans | Secured by multi-family residences
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	10,440	10,650
Real estate loans | Secured by multi-family residences | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	10,440	10,650
Real estate loans | Secured by multi-family residences | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans | Secured by multi-family residences | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans | Secured by multi-family residences | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,530	10,750
Real estate loans | Construction | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,530	10,750
Real estate loans | Construction | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans | Construction | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans | Construction | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	17,046	14,803
Real estate loans | Commercial real estate | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	16,099	14,803
Real estate loans | Commercial real estate | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	947	0
Real estate loans | Commercial real estate | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans | Commercial real estate | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans | Home equity lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	16,528	17,127
Real estate loans | Home equity lines of credit | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	16,316	16,897
Real estate loans | Home equity lines of credit | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Real estate loans | Home equity lines of credit | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	212	230
Real estate loans | Home equity lines of credit | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Other Loans Portfolio Segment | Commercial & industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,260	3,679
Other Loans Portfolio Segment | Commercial & industrial loans | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,215	3,679
Other Loans Portfolio Segment | Commercial & industrial loans | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	45	0
Other Loans Portfolio Segment | Commercial & industrial loans | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Other Loans Portfolio Segment | Commercial & industrial loans | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Other Loans Portfolio Segment | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	55	70
Other Loans Portfolio Segment | Other loans | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	55	70
Other Loans Portfolio Segment | Other loans | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Other Loans Portfolio Segment | Other loans | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	0
Other Loans Portfolio Segment | Other loans | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 0	$ 0