Segment Reporting - Reconciliation of Segment Earnings to Earnings Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Operating earnings (losses)	$ (5,747)	$ 7,800	$ 1,408
General and administrative	(10,284)	(10,198)	(8,937)
Gain on dissolution of investment	0	573	0
Interest income	656	2,766	2,155
Interest expense	(444)	(636)	(109)
(Losses) earnings before income taxes	(5,535)	10,503	3,454
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Operating earnings (losses)	4,537	17,998	10,345
Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Operating earnings (losses)	0	0	0
Segment Reconciling Items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gain on dissolution of investment	0	573	0
Interest income	656	2,766	2,155
Interest expense	$ (444)	$ (636)	$ (109)