Summary of Significant Accounting Policies - Basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator:
Net income (loss)	$ 3,253	$ 758	$ (4,911)	$ 1,680	$ 4,011	$ (3,231)
Less: Income (loss) allocated to unvested participating securities	35		(104)		43	(68)
Net income (loss) available to common stockholders	$ 3,218		$ (4,807)		$ 3,968	$ (3,163)
Denominator:
Denominator for basic earnings per share ??? weighted average shares	5,917		5,868		5,915	5,867
Effect of dilutive securities:
Common stock equivalents	0		0		0	0
Denominator for diluted earnings per share ??? adjusted weighted-average shares and assumed conversions	5,917		5,868		5,915	5,867
Basic earnings (loss) per share
Basic	$ 0.54		$ (0.82)		$ 0.67	$ (0.54)
Diluted earnings (loss) per share
Diluted earning per share	$ 0.54		$ (0.82)		$ 0.67	$ (0.54)