Segment Reporting - Reconciliation of Segment Earnings to Earnings Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Operating earnings (losses)	$ 7,800	$ 1,408	$ 1,502
General and administrative	(10,198)	(8,937)	(9,707)
Loss on deconsolidation of subsidiary	0	0	(3,505)
Impairment of investment in unconsolidated affiliate	0	0	(2,500)
Gain on dissolution of investment	573	0	0
Interest income	2,766	2,155	1,103
Interest expense	(636)	(109)	(27)
(Losses) earnings before income taxes	10,503	3,454	(3,427)
Voluntary early retirement program expense			400
Selling and Administrative Expenses
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Voluntary early retirement program expense			1,000
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Operating earnings (losses)	17,998	10,345	11,209
Segment Reconciling Items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Loss on deconsolidation of subsidiary	0	0	(3,505)
Impairment of investment in unconsolidated affiliate	0	0	(2,500)
Gain on dissolution of investment	573	0	0
Interest income	2,766	2,155	1,103
Interest expense	$ (636)	$ (109)	$ (27)