CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 20,121	$ 23,802	$ 22,974
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	43,755	37,425	35,929
Losses (gains) on sales and/or abandonment of property and equipment	530	(23)	916
Write-off of patents and intangible assets	101	141	1,427
Acquired in-process research and development	461	1,000	0
Amortization of deferred credits	(170)	(171)	(175)
Amortization of long-term debt issuance costs	952	987	987
Deferred income taxes	(962)	3,450	3,870
Excess tax benefits from stock-based compensation	(669)	(2,124)	(576)
Stock-based compensation expense	2,506	2,243	1,460
Changes in operating assets and liabilities, net of effects from acquisitions:
Trade receivables	(6,816)	(5,872)	(13,599)
Employee receivables	15	(52)	46
Other receivables	1,146	387	(3,042)
Inventories	(3,656)	(13,113)	(9,396)
Prepaid expenses	271	(696)	(58)
Prepaid income taxes	404	(1,788)	(41)
Income tax refund receivables	406	(784)	11
Other assets	(3,763)	(362)	(1,388)
Trade payables	(6,835)	14,766	5,326
Accrued expenses	3,245	5,656	6,137
Advances from employees	(3)	217	142
Income taxes payable	1,451	2,199	1,083
Liabilities related to unrecognized tax benefits	597	536	(76)
Deferred compensation payable	712	(135)	802
Other long-term obligations	(200)	1,769	566
Total adjustments	33,478	45,656	30,351
Net cash provided by operating activities	53,599	69,458	53,325
Capital expenditures for:
Property and equipment	(32,837)	(50,959)	(34,181)
Intangible assets	(2,217)	(1,956)	(1,714)
Proceeds from sale-leaseback transactions	0	2,017	5,521
Proceeds from Sale of Other Assets, Investing Activities	1,089	0	0
Proceeds from the sale of property and equipment	19	1,247	98
Cash paid in acquisitions, net of cash acquired	(125,161)	(12,368)	(5,927)
Net cash used in investing activities	(159,107)	(62,019)	(36,203)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	5,271	6,668	8,146
Proceeds from issuance of long-term debt	219,505	152,375	144,018
Payments on long-term debt	(102,098)	(169,272)	(169,392)
Excess tax benefits from stock-based compensation	669	2,124	576
Long-term debt issuance costs	(1,948)	0	0
Contingent payments related to acquisitions	(218)	(1,212)	(67)
Payment of taxes related to an exchange of common stock	(86)	(918)	(249)
Net cash provided by (used in) financing activities	121,095	(10,235)	(16,968)
EFFECT OF EXCHANGE RATES ON CASH	(593)	(382)	(258)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	14,994	(3,178)	(104)
CASH AND CASH EQUIVALENTS:
Beginning of year	4,177	7,355	7,459
End of year	19,171	4,177	7,355
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest (net of capitalized interest of $460, $325 and $389, respectively)	8,872	6,273	9,014
Income taxes	2,318	3,409	3,289
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING ACTIVITIES
Property and equipment purchases in accounts payable	2,398	3,199	2,896
Receivable due for sale of equipment	0	0	1,256
Cost method investment converted to intangible asset in acquisition in lieu of additional cash payment	0	1,010	0
Contingent receivable in exchange for sale of cost method investment	711	0	0
Acquisition purchases in accrued expenses and other long-term obligations	0	1,300	1,000
Merit common stock surrendered (14, 185 and 127 shares, respectively) in exchange for exercise of stock options	$ 346	$ 3,802	$ 1,941