Statements of Income - USD ($)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Revenue
Revenue	$ 29,863,881	$ 28,326,196	$ 27,717,278
Cost of sales	6,274,744	6,078,294	6,616,852
Gross profit	23,589,137	22,247,902	21,100,426
Expenses
Selling, general, and administrative	1,435,592	1,458,598	1,752,962
Research and development	3,702,918	3,344,101	3,061,184
Total expenses	5,138,510	4,802,699	4,814,146
Income from operations	18,450,627	17,445,203	16,286,280
Interest income	1,558,197	1,650,808	1,890,817
Income before taxes	20,008,824	19,096,011	18,177,097
Provision for income taxes	6,096,152	6,147,142	5,884,782
Net income	$ 13,912,672	$ 12,948,869	$ 12,292,315
Net income per share – basic (in dollars per share)	$ 2.87	$ 2.68	$ 2.53
Net income per share – diluted (in dollars per share)	2.87	2.68	2.53
Cash dividends declared per common share (in dollars per share)	$ 4	$ 4	$ 4
Weighted average shares outstanding
Basic (in shares)	4,841,347	4,836,602	4,850,209
Diluted (in shares)	4,846,212	4,838,389	4,852,602
Product [Member]
Revenue
Revenue	$ 27,321,810	$ 26,182,453	$ 24,410,391
Contract Research and Development [Member]
Revenue
Revenue	$ 2,542,071	$ 2,143,743	$ 3,306,887