Loans - Risk category of loans by class (Details 1) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 267,899	$ 263,973
Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	264,513	260,664
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,070	116
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,316	3,193
Doubtful
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	263,700	260,224
Real estate loans: | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	260,314	256,915
Real estate loans: | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,070	116
Real estate loans: | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,316	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	211,265	206,894
Real estate loans: | Secured by one-to-four family residences | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	209,049	203,815
Real estate loans: | Secured by one-to-four family residences | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	115	116
Real estate loans: | Secured by one-to-four family residences | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,101	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	10,499	10,650
Real estate loans: | Secured by multi-family residences | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	10,499	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	8,401	10,750
Real estate loans: | Construction | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,401	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	16,713	14,803
Real estate loans: | Commercial real estate | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	15,758	14,803
Real estate loans: | Commercial real estate | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	955	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	16,822	17,127
Real estate loans: | Home equity lines of credit | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	16,607	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	215	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	4,142	3,679
Other Loans Portfolio Segment | Commercial & industrial loans | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,142	3,679
Other Loans Portfolio Segment | Commercial & industrial loans | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0	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	57	70
Other Loans Portfolio Segment | Other loans | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	57	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