Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income from consolidated operations	$ 13,369	$ 19,750	$ 14,311
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	8,268	8,172	7,831
Loss (gain) on sales of property, plant and equipment	459	0	(47)
Share-based compensation	1,807	1,591	1,212
Interest expense on finance leases	2	0	0
Deferred income taxes	136	792	1,881
Changes in operating assets and liabilities:
Receivables, net	2,220	(327)	(2,556)
Inventories	(366)	1,300	(2,295)
Prepaid expenses	(256)	(98)	(249)
Refundable income taxes	295	2,006	(1,268)
Other assets	(73)	110	(76)
Accounts payable	(681)	(2,472)	1,113
Accrued expenses	(539)	25	1,472
Deferred revenue	(687)	67	35
Non-qualified deferred compensation plan and other liabilities	1,083	313	(44)
Net cash provided by operating activities	25,037	31,229	21,320
Cash flows from investing activities:
Additions to property, plant and equipment	(4,368)	(5,778)	(5,428)
Acquisition of Dieletrics, net of cash acquired	0	0	(76,978)
Proceeds from sale of property, plant and equipment	107	4	77
Net cash used in investing activities	(4,261)	(5,774)	(82,329)
Cash flows from financing activities:
Proceeds from advances on revolving line of credit	5,500	0	36,000
Payments on revolving line of credit	(5,500)	(8,000)	(28,000)
Proceeds from the issuance of long-term debt	0	0	20,000
Principal repayment of long-term debt	0	(17,143)	(2,857)
Principal payments on finance lease obligations	(11)	0	0
Proceeds from the exercise of stock options	474	705	1,270
Payment of statutory withholding for restricted stock units vested	(748)	(512)	(144)
Net cash (used in) provided by financing activities	(285)	(24,950)	26,269
Net change in cash and cash equivalents	20,491	505	(34,740)
Cash and cash equivalents at beginning of year	3,743	3,238	37,978
Cash and cash equivalents at end of year	$ 24,234	$ 3,743	$ 3,238