Segment Reporting - Reconciliation of Segment Earnings to Earnings Before Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Abstract]
Operating (losses) earnings	$ 6,056	$ 303	$ (10,949)	$ 4,913
Gain on dissolution of investment	0	0	0	573
Interest income	105	758	614	2,145
Interest expense	(70)	(242)	(288)	(424)
(Losses) Earnings before income taxes	6,091	819	(10,623)	7,207
Operating Segments
Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Abstract]
Operating (losses) earnings	7,461	3,042	(3,919)	12,918
General and administrative
Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Abstract]
Operating (losses) earnings	(1,405)	(2,739)	(7,030)	(8,005)
Segment reconciling items
Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Abstract]
Gain on dissolution of investment	0	0	0	573
Interest income	105	758	614	2,145
Interest expense	$ (70)	$ (242)	$ (288)	$ (424)