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, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic earnings per share:
Net earnings	$ 640	$ 6	$ 4,908	$ 2,035	$ 3,620	$ 1,138	$ 5,554	$ 6,793
Basic weighted average number of shares outstanding (in shares)	4,234			4,218			4,226	4,218
Basic earnings per share (in dollars per share)	$ 0.15			$ 0.48			$ 1.31	$ 1.61
Diluted weighted average number of shares outstanding:
Basic weighted average number of shares outstanding (in shares)	4,234			4,218			4,226	4,218
Total (in shares)	4,238			4,219			4,230	4,218
Diluted earnings per share (in dollars per share)	$ 0.15			$ 0.48			$ 1.31	$ 1.61
Restricted stock unit awards
Diluted weighted average number of shares outstanding:
Unit awards	3			1			4	0
Performance Unit Awards
Diluted weighted average number of shares outstanding:
Unit awards	1			0			0	0