CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenues	$ 146,595	$ 143,487	$ 145,733
Cost of Goods Sold	75,841	75,857	74,752
Gross Profit	70,754	67,630	70,981
Operating Expenses:
Selling	7,251	6,611	6,043
General and administrative	16,430	15,319	16,082
Research and development	5,799	6,574	6,346
Operating Expenses, Total	29,480	28,504	28,471
Operating Income	41,274	39,126	42,510
Interest Income	1,065	448	771
Other Income (Expense), net	1	(308)	(2,411)
Income before Provision for Income Taxes	42,340	39,266	40,870
Provision for Income Taxes	(5,747)	(11,685)	(11,945)
Net Income	$ 36,593	$ 27,581	$ 28,925
Net Income Per Basic Share	$ 19.82	$ 15.12	$ 15.67
Weighted Average Basic Shares Outstanding	1,846	1,824	1,846
Net Income Per Diluted Share	$ 19.71	$ 14.85	$ 15.47
Weighted Average Diluted Shares Outstanding	1,857	1,857	1,870
Dividends Per Common Share	$ 4.5	$ 3.9	$ 3.3