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, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic earnings per share:
Net earnings	$ 6	$ 4,908	$ 3,620	$ 1,138	$ 4,914	$ 4,758
Basic weighted average number of shares outstanding (in shares)	4,227		4,218		4,223	4,218
Basic earnings per share (in dollars per share)	$ 0		$ 0.86		$ 1.16	$ 1.13
Diluted weighted average number of shares outstanding:
Basic weighted average number of shares outstanding (in shares)	4,227		4,218		4,223	4,218
Total (in shares)	4,227		4,218		4,229	4,218
Diluted earnings per share (in dollars per share)	$ 0		$ 0.86		$ 1.16	$ 1.13
Restricted stock unit awards
Diluted weighted average number of shares outstanding:
Unit awards	0		0		6	0
Performance Unit Awards
Diluted weighted average number of shares outstanding:
Unit awards	0		0		0	0