Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
OPERATING ACTIVITIES:
Net income	$ 37,045	$ 28,223	$ 26,056
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	20,898	19,611	17,617
Impairment of long-lived assets		1,550	930
Amortization of deferred financing costs	6	5	9
Deferred income taxes	1,524	4,313	4,848
Loss on disposition of property, plant and equipment	10	462	439
Stock-based compensation	2,236	1,915	1,524
Changes in operating assets and liabilities:
Trade receivables, net	(3,736)	1,109	(3,346)
Inventories, net	94	(1,390)	(542)
Prepaid expenses and other current assets	(999)	(106)	(447)
Other assets	(41)	3	117
Accounts payable and accrued expenses	(1,101)	2,579	(165)
Other liabilities	(247)	301	(29)
Net cash provided by operating activities	55,689	58,575	47,011
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(29,914)	(17,133)	(27,100)
Acquisition of a business		(8,392)
Proceeds from sale of property, plant and equipment	285	331	558
Net cash used in investing activities	(29,629)	(25,194)	(26,542)
FINANCING ACTIVITIES:
Cash dividends paid	(3,620)	(3,603)	(33,058)
Proceeds from exercise of stock options	84	81	75
Purchase of treasury shares	(731)	(557)	(444)
Net cash used in financing activities	(4,267)	(4,079)	(33,427)
Net increase (decrease) in cash and cash equivalents	21,793	29,302	(12,958)
Cash and cash equivalents at beginning of period	83,562	54,260	67,218
Cash and cash equivalents at end of period	$ 105,355	$ 83,562	$ 54,260