Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands	6 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Cash flows from operating activities:
Net income	$ 9,450	$ 15,393
Adjustments to reconcile net income to cash provided by operating activities, net of the effects of the acquisition of Psytechnics:
Depreciation and amortization	7,977	6,875
Loss on disposal of fixed assets	127	76
Share-based compensation expense associated with equity awards	3,947	2,679
Deferred income taxes	1,163	2,338
Other losses (gains)	(67)	0
Changes in assets and liabilities
Accounts receivable	13,583	24,108
Inventories	(1,948)	(3,579)
Prepaid expenses and other current assets	463	1,100
Accounts payable	(1,329)	(892)
Accrued compensation and other expenses	(5,205)	(2,501)
Deferred revenue	(10,233)	(15,013)
Net cash provided by operating activities	17,928	30,584
Cash flows from investing activities:
Purchase of marketable securities	(67,380)	(29,146)
Proceeds from maturity of marketable securities	133,839	55,660
Purchase of fixed assets	(5,792)	(2,610)
Acquisition of Psytechnics, net of cash acquired	(16,945)	0
Net cash provided by investing activities	43,722	23,904
Cash flows from financing activities:
Proceeds from the exercise of stock options	196	593
Treasury stock repurchases	(17,797)	0
Repayment of long-term debt	(7,500)	(5,000)
Excess tax benefit from stock options exercised	142	640
Net cash used in financing activities	(24,959)	(3,767)
Net increase (decrease) in cash and cash equivalents	36,691	50,721
Cash and cash equivalents, beginning of period	67,168	63,322
Cash and cash equivalents, end of period	103,859	114,043
Supplemental disclosure of cash flow information:
Cash paid for interest	842	1,787
Cash paid for income taxes	3,934	5,318
Non-cash transactions:
Transfers of inventory to fixed assets	1,910	1,348
Additions to property, plant and equipment included in accounts payable	$ 96	$ 0