CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF INCOME
Revenues	$ 147,591,000	$ 155,066,000	$ 152,448,000
Cost of Goods Sold	81,428,000	84,378,000	80,670,000
Gross Profit	66,163,000	70,688,000	71,778,000
Operating Expenses:
Selling	7,520,000	8,813,000	8,341,000
General and administrative	17,330,000	16,308,000	16,217,000
Research and development	5,645,000	5,038,000	5,513,000
Total operating expense	30,495,000	30,159,000	30,071,000
Operating Income	35,668,000	40,529,000	41,707,000
Interest and Dividend Income	1,444,000	2,487,000	1,667,000
Other Investment Income (Loss)	1,355,000	152,000	(1,380,000)
Other Income	0	0	42,000
Income before Provision for Income Taxes	38,467,000	43,168,000	42,036,000
Provision for Income Taxes	(6,352,000)	(6,407,000)	(7,781,000)
Net Income	$ 32,115,000	$ 36,761,000	$ 34,255,000
Net Income Per Basic Share	$ 17.49	$ 19.82	$ 18.49
Weighted Average Basic Shares Outstanding	1,836	1,855	1,853
Net Income Per Diluted Share	$ 17.44	$ 19.73	$ 18.44
Weighted Average Diluted Shares Outstanding	1,841	1,863	1,858
Dividends Per Common Share	$ 6.60	$ 5.80	$ 5.10