Summary of Significant Accounting Policies - Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net earnings	$ 5,846	$ 3,073	$ 3,503	$ (11,427)	$ 2,653	$ 640	$ 6	$ 4,908	$ 995	$ 8,207	$ 2,945
Basic weighted average number of shares outstanding (in shares)									4,240	4,228	4,218
Basic earnings per share (in dollars per share)	$ 1.38	$ 0.72	$ 0.83	$ (2.70)	$ 0.63	$ 0.15	$ 0	$ 1.16	$ 0.23	$ 1.94	$ 0.70
Diluted weighted average number of shares outstanding (in shares)									4,254	4,233	4,218
Diluted earnings per share (in dollars per share)	$ 1.37	$ 0.72	$ 0.82	$ (2.69)	$ 0.63	$ 0.15	$ 0	$ 1.16	$ 0.23	$ 1.94	$ 0.70
Restricted stock units awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units award (in shares)									11	5	0
Performance share unit awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units award (in shares)									3	0	0