Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
OPERATING ACTIVITIES:
Net income	$ 26,056	$ 19,685	$ 27,148
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	17,617	17,603	16,549
Impairment of long-lived assets	930
Amortization of deferred financing costs	9	14	15
Deferred income taxes	4,848	20	(7,612)
Loss on disposition of property, plant and equipment	439	624	377
Stock-based compensation	1,524	1,489	1,405
Changes in operating assets and liabilities:
Trade receivables, net	(3,346)	(3,129)	308
Inventories, net	(542)	700	(1,113)
Prepaid expenses and other current assets	(447)	1,377	(1,594)
Other assets	117	(1)	5
Accounts payable and accrued expenses	(165)	438	(1,130)
Other liabilities	(29)	(85)	(76)
Net cash provided by operating activities	47,011	38,735	34,282
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(27,100)	(53,762)	(21,337)
Proceeds from sale of property, plant and equipment	558	605	592
Net cash used in investing activities	(26,542)	(53,157)	(20,745)
FINANCING ACTIVITIES:
Cash dividends paid	(33,058)	(3,022)	(3,013)
Proceeds from exercise of stock options	75	73	73
Purchase of treasury shares	(444)	(411)	(309)
Net cash used in financing activities	(33,427)	(3,360)	(3,249)
Net (decrease) increase in cash and cash equivalents	(12,958)	(17,782)	10,288
Cash and cash equivalents at beginning of period	67,218	85,000	74,712
Cash and cash equivalents at end of period	$ 54,260	$ 67,218	$ 85,000