Summary of Significant Accounting Policies - Reconciliation of Basic and Diluted Earnings (Losses) per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic earnings per share:
Net (losses) earnings	$ 3,073	$ 3,503	$ (11,427)	$ 640	$ 6	$ 4,908	$ (4,851)	$ 5,554
Basic weighted average number of shares outstanding (in shares)	4,242			4,234			4,239	4,226
Basic earnings per share (in dollars per share)	$ 0.72			$ 0.15			$ (1.14)	$ 1.31
Diluted weighted average number of shares outstanding:
Basic weighted average number of shares outstanding (in shares)	4,242			4,234			4,239	4,226
Total diluted shares (in shares)	4,253			4,238			4,239	4,230
Diluted earnings per share (in dollars per share)	$ 0.72			$ 0.15			$ (1.14)	$ 1.31
Restricted stock units awards
Diluted weighted average number of shares outstanding:
Unit awards (in shares)	9			3			0	4
Performance share unit awards
Diluted weighted average number of shares outstanding:
Unit awards (in shares)	2			1			0	0