Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES:
Net income	$ 28,223	$ 26,056	$ 19,685
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	19,611	17,617	17,603
Impairment of long-lived assets	1,550	930
Amortization of deferred financing costs	5	9	14
Deferred income taxes	4,313	4,848	20
Loss on disposition of property, plant and equipment	462	439	624
Stock-based compensation	1,915	1,524	1,489
Changes in operating assets and liabilities:
Trade receivables, net	1,109	(3,346)	(3,129)
Inventories, net	(1,390)	(542)	700
Prepaid expenses and other current assets	(106)	(447)	1,377
Other assets	3	117	(1)
Accounts payable and accrued expenses	2,579	(165)	438
Other liabilities	301	(29)	(85)
Net cash provided by operating activities	58,575	47,011	38,735
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(17,133)	(27,100)	(53,762)
Acquisition of a business	(8,392)
Proceeds from sale of property, plant and equipment	331	558	605
Net cash used in investing activities	(25,194)	(26,542)	(53,157)
FINANCING ACTIVITIES:
Cash dividends paid	(3,603)	(33,058)	(3,022)
Proceeds from exercise of stock options	81	75	73
Purchase of treasury shares	(557)	(444)	(411)
Net cash used in financing activities	(4,079)	(33,427)	(3,360)
Net increase (decrease) in cash and cash equivalents	29,302	(12,958)	(17,782)
Cash and cash equivalents at beginning of period	54,260	67,218	85,000
Cash and cash equivalents at end of period	$ 83,562	$ 54,260	$ 67,218