CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
OPERATING ACTIVITIES:
Net income	$ 5,544	$ 5,128
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	4,655	4,121
Amortization of deferred financing costs	2	4
Deferred income taxes	990	1,246
(Gain) loss on disposition of property, plant and equipment	(13)	386
Stock-based compensation	379	309
Changes in operating assets and liabilities:
Trade receivables, net	(200)	(3,108)
Inventories, net	(146)	25
Prepaid expenses and other current assets	249	216
Other assets	14	31
Accounts payable and accrued expenses	21	(899)
Other liabilities	13	15
Net cash provided by operating activities	11,508	7,474
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(6,106)	(5,684)
Proceeds from sale of property, plant and equipment	16	142
Net cash used in investing activities	(6,090)	(5,542)
FINANCING ACTIVITIES:
Cash dividends paid	(899)	(757)
Proceeds from exercise of stock options	81
Purchase of treasury shares	(64)	(52)
Net cash used in financing activities	(882)	(809)
Net increase in cash and cash equivalents	4,536	1,123
Cash and cash equivalents at beginning of period	54,260	67,218
Cash and cash equivalents at end of period	$ 58,796	$ 68,341