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				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic earnings per share:
Net (losses) earnings	$ 3,503	$ (11,427)	$ 6	$ 4,908	$ (7,924)	$ 4,914
Basic weighted average number of shares outstanding (in shares)	4,239		4,227		4,237	4,223
Basic earnings per share (in dollars per share)	$ 0.83		$ 0		$ (1.87)	$ 1.16
Diluted weighted average number of shares outstanding:
Basic weighted average number of shares outstanding (in shares)	4,239		4,227		4,237	4,223
Total diluted shares (in shares)	4,253		4,227		4,237	4,229
Diluted earnings per share (in dollars per share)	$ 0.82		$ 0		$ (1.87)	$ 1.16
Restricted stock units awards
Diluted weighted average number of shares outstanding:
Unit awards (in shares)	12		0		0	6
Performance share unit awards
Diluted weighted average number of shares outstanding:
Unit awards (in shares)	2		0		0	0