Fair Value Disclosure (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized gain (loss) on the Mine Water Treatment Trust	$ 108	$ 397	$ 1,067	$ 481
Bellaire Corporation | Level 1 | Fair value measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mine Water Treatment Trust					$ 5,000
Realized gain (loss) on the Mine Water Treatment Trust	$ 100	$ 400	$ 1,100	$ 500