Segment Reporting - Reconciliation of segment earnings to earnings before income taxes (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
Aug. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Operating earnings (losses)		$ 1,408	$ 1,502	$ 6,054
Loss on deconsolidation of subsidiary		0	(3,505)	0
Impairment of investment in unconsolidated affiliate		0	(2,500)	0
Interest income		2,155	1,103	582
Interest expense		(109)	(27)	(2)
(Losses) earnings before income taxes and investment in unconsolidated affiliate		3,454	(3,427)	6,634
Voluntary early retirement program expense	$ 400		1,000
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Operating earnings (losses)		10,345	11,209	16,464
Corporate, Non-Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Operating earnings (losses)		(8,937)	(9,707)	(10,410)
Segment Reconciling Items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Loss on deconsolidation of subsidiary		0	(3,505)	0
Impairment of investment in unconsolidated affiliate		0	(2,500)	0
Interest income		2,155	1,103	582
Interest expense		$ (109)	$ (27)	$ (2)

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Amount of gain (loss) from deconsolidation of subsidiary and derecognition of group of assets constituting transfer of business or nonprofit activity, excluding conveyance of oil and gas mineral rights and transfer of good or service in contract with customer.

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Amount of the cost of borrowed funds accounted for as interest expense.

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Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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The net result for the period of deducting operating expenses from operating revenues.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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