Fair Value Disclosure (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain on equity securities	$ 3,423	$ 1,226
Long-term debt fair value	20,500	45,200
Long-term Debt	20,370	45,000
Mineral Management
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived asset write off		7,300
Coal Mining customer
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived asset write off		1,100
Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain on equity securities	1,700	100
Level 1 | Fair Value, Measurements, Recurring | Reported Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in equity securities		2,000
Level 1 | Fair Value, Measurements, Recurring | Bellaire
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain on equity securities	$ 1,700	$ 1,200