CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
OPERATING ACTIVITIES:
Net income	$ 5,128	$ 4,262
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	4,121	4,230
Amortization of deferred financing costs	4	8
Deferred income taxes	1,246	471
Loss on disposition of property, plant and equipment	386	211
Stock-based compensation	309	316
Changes in operating assets and liabilities:
Trade receivables, net	(3,108)	(2,601)
Inventories, net	25	947
Prepaid expenses and other current assets	216	417
Other assets	31	20
Accounts payable and accrued expenses	(899)	(1,705)
Other liabilities	15	(56)
Net cash provided by operating activities	7,474	6,520
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(5,684)	(7,620)
Proceeds from sale of property, plant and equipment	142	108
Net cash used in investing activities	(5,542)	(7,512)
FINANCING ACTIVITIES:
Cash dividends paid	(757)	(755)
Proceeds from exercise of stock options		73
Purchase of treasury shares	(52)	(61)
Net cash used in financing activities	(809)	(743)
Net increase (decrease) in cash and cash equivalents	1,123	(1,735)
Cash and cash equivalents at beginning of period	67,218	85,000
Cash and cash equivalents at end of period	$ 68,341	$ 83,265