CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenues	$ 152,448	$ 146,595	$ 143,487
Cost of Goods Sold	80,670	75,841	75,857
Gross Profit	71,778	70,754	67,630
Operating Expenses:
Selling	8,341	7,251	6,611
General and administrative	16,217	16,430	15,319
Research and development	5,513	5,799	6,574
Operating Expenses, Total	30,071	29,480	28,504
Operating Income	41,707	41,274	39,126
Interest and Dividend Income	1,667	1,061	448
Other Investment Income (Loss)	(1,380)	4	(311)
Other Income (Expense), net	42	1	3
Income before Provision for Income Taxes	42,036	42,340	39,266
Provision for Income Taxes	(7,781)	(5,747)	(11,685)
Net Income	$ 34,255	$ 36,593	$ 27,581
Net Income Per Basic Share	$ 18.49	$ 19.82	$ 15.12
Weighted Average Basic Shares Outstanding	1,853	1,846	1,824
Net Income Per Diluted Share	$ 18.44	$ 19.71	$ 14.85
Weighted Average Diluted Shares Outstanding	1,858	1,857	1,857
Dividends Per Common Share	$ 5.1	$ 4.5	$ 3.9