Summary of Significant Accounting Policies - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income	$ 3,334	$ 3,695	$ 9,438	$ 9,395
Less: Income allocated to unvested participating securities	61	63	173	160
Net income available to common stockholders	$ 3,273	$ 3,632	$ 9,265	$ 9,235
Denominator:
Denominator for basic earnings per share - weighted average shares	5,834	5,822	5,840	5,833
Effect of dilutive securities:
Denominator for diluted earnings per share - adjusted weighted-average shares and assumed conversions	5,834	5,822	5,840	5,833
Earnings per share:
Basic	$ 0.56	$ 0.62	$ 1.59	$ 1.58
Diluted	$ 0.56	$ 0.62	$ 1.59	$ 1.58