Income Taxes (Reconciliation of the Federal Statutory and Effective Income Tax Rate) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income before income tax provision	$ 14,258	$ 43,399
Statutory taxes at 21.0%	2,994	9,114
State and local income taxes	(626)	1,129
Non-deductible expenses	426	736
Percentage depletion	(3,744)	(4,451)
R&D and other federal credits	(367)	(255)
Settlements and uncertain tax positions	6,286	(2,377)
Coronavirus Aid, Relief, and Economic Security ("CARES") Act - carryback rate differential	(4,741)	0
Other, net	(763)	(129)
Income tax provision	$ (535)	$ 3,767
Effective income tax rate	(3.80%)	8.70%