Fair Value Disclosure (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	May 02, 2022	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Income from privately-held company's earnings and immaterial basis difference adjustments	$ 2,156	$ 0	$ 2,156	$ 0
Carrying amount of long-lived asset after impairment	0		0
Private Equity Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Income from privately-held company's earnings and immaterial basis difference adjustments	2,200
Mineral Management
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-cash asset impairment charge	3,900
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on equity securities	200	400	1,000	1,600
Significant Unobservable Inputs (Level 3) | Fair value measurements, nonrecurring | Coal Mining
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment					$ 5,000
Fair value of privately-held company					12,800
Significant Unobservable Inputs (Level 3) | Fair value measurements, nonrecurring | Mineral Management
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value gained from contract termination					$ 4,100
Bellaire | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on equity securities	$ (500)	$ 100	$ (2,700)	$ 1,000
Carrying Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities cost						$ 2,000
Carrying Value | Bellaire | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities cost						$ 5,000