Summary of Significant Accounting Policies - Basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Numerator:
Net income	$ 758	$ 1,680
Less: Income allocated to unvested participating securities	8	37
Net income available to common stockholders	$ 750	$ 1,643
Denominator:
Denominator for basic earnings per share - weighted average shares	5,913	5,866
Effect of dilutive securities:
Common stock equivalents	0	0
Denominator for diluted earnings per share - adjusted weighted-average shares and assumed conversions	5,913	5,866
Basic earnings per share:
Basic	$ 0.13	$ 0.28
Diluted earnings per share
Diluted earning per share	$ 0.13	$ 0.28

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