Segment Reporting - Reconciliation of Segment Earnings to Earnings Before Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Abstract]
Operating earnings	$ 303	$ 2,239	$ 4,913	$ 7,614
Gain on dissolution of investment	0	0	573	0
Interest income	758	601	2,145	1,486
Interest expense	(242)	(26)	(424)	(60)
Earnings before income taxes	819	2,814	7,207	9,040
Reporting Segments
Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Abstract]
Operating earnings	3,042	3,772	12,918	13,714
General and administrative
Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Abstract]
Operating earnings	(2,739)	(1,533)	(8,005)	(6,100)
Segment reconciling items
Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Abstract]
Gain on dissolution of investment	0	0	573	0
Interest income	758	601	2,145	1,486
Interest expense	$ (242)	$ (26)	$ (424)	$ (60)

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 income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

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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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