Summary of Significant Accounting Policies - Reconciliation of Basic and Diluted Earnings (Losses) per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic earnings (losses) per share:
Net earnings (losses)	$ 3,620	$ (282)	$ 4,758	$ (1,142)
Weighted average number of shares outstanding – Basic (in shares)	4,218,000	4,218,000	4,218,000	4,218,000
Basic earnings (losses) per share (in dollars per share)	$ 0.86	$ (0.07)	$ 1.13	$ (0.27)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net (losses) earnings	$ 3,620	$ (282)	$ 4,758	$ (1,142)
Diluted earnings (losses) per share:
Total (in shares)	4,218,000	4,218,000	4,218,000	4,218,000
Diluted earnings (losses) per share (in dollars per share)	$ 0.86	$ (0.07)	$ 1.13	$ (0.27)
Restricted stock units awards
Diluted earnings (losses) per share:
Unit awards	0	0	0	0
Performance share unit awards
Diluted earnings (losses) per share:
Unit awards	0	0	0	0

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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