CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Net sales and contract revenues:
Net product sales and contract revenues	$ 98,489	$ 114,124	$ 192,818
Net service revenues	88,191	89,428	85,758
Total net sales and contract revenues	186,680	203,552	278,576
Cost of sales and contracts:
Cost of product sales and contracts	68,214	65,500	104,062
Cost of service revenues	39,047	44,935	45,312
Total cost of sales and contracts	107,261	110,435	149,374
Gross profit	79,419	93,117	129,202
Operating expenses:
Selling, general and administrative expenses	29,533	35,624	42,139
Research and development expenses	23,618	25,544	22,619
Total operating expenses	53,151	61,168	64,758
Operating income	26,268	31,949	64,444
Other income (expense):
Interest and investment income, net	657	655	678
Interest expense	(65)	(91)	(110)
Other, net	(414)	(55)	(137)
Total other income	178	509	431
Income before provision for income taxes	26,446	32,458	64,875
Provision for income taxes	8,992	11,036	22,058
Net income	17,454	21,422	42,817
Other comprehensive income (loss):
Unrealized gain (loss) on available for sale securities (net of tax)	(20)	(5)	(12)
Comprehensive income	$ 17,434	$ 21,417	$ 42,805
Income per share - Basic (in dollars per share)	$ 2.08	$ 2.37	$ 4.73
Income per share - Diluted (in dollars per share)	$ 2.07	$ 2.34	$ 4.63
Weighted average shares - Basic (in shares)	8,394	9,046	9,045
Weighted average shares - Diluted (in shares)	8,448	9,148	9,247
Dividends declared per share (in dollars per share)	$ 2.00	$ 1.60	$ 1.20