CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
OPERATING ACTIVITIES:
Net income	$ 18,124	$ 11,645
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	10,575	9,453
Amortization of deferred financing costs	2	2
Deferred income taxes	1,779	2,484
(Gain) loss on disposition of property, plant and equipment	(78)	239
Stock-based compensation	1,118	842
Changes in operating assets and liabilities:
Trade receivables, net	(4,483)	1,756
Inventories, net	587	(1,034)
Prepaid expenses and other current assets	445	896
Other assets	(132)	40
Accounts payable and accrued expenses	(618)	779
Other liabilities	53	27
Net cash provided by operating activities	27,372	27,129
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(17,776)	(10,599)
Proceeds from sale of property, plant and equipment	10	46
Net cash used in investing activities	(17,766)	(10,553)
FINANCING ACTIVITIES:
Cash dividends paid	(1,809)	(1,800)
Proceeds from exercise of stock options	83	81
Purchase of treasury shares	(95)	(282)
Net cash used in financing activities	(1,821)	(2,001)
Net increase in cash and cash equivalents	7,785	14,575
Cash and cash equivalents at beginning of period	83,562	54,260
Cash and cash equivalents at end of period	$ 91,347	$ 68,835