CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Cash flows from operating activities:
Net income	$ 13,091	$ 14,537	$ 13,023
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	5,090	4,562	4,935
Investment premium amortization, net	986	526	211
Net loss on disposals of property and equipment	13	16	104
Net loss (gain) on foreign exchange translation	144	(275)	60
Share-based compensation expense	5,683	4,844	5,337
Excess tax benefits from share-based awards	(862)	(2,260)	(2,096)
Provision for deferred income taxes	673	2,087	1,245
Equity in net loss of unconsolidated affiliate	143	31	0
Changes in assets and liabilities:
Receivables, net	(2,827)	(4,132)	(1,833)
Inventories	(1,236)	(1,846)	(5,068)
Prepaid expenses and other current assets	(1,199)	(156)	(585)
Other assets	44	(55)	(52)
Accounts payable	232	(3,248)	5,436
Accrued payroll and related expenses	208	514	1,917
Accrued taxes	(276)	582	884
Other accrued liabilities	299	336	140
Deferred rent	225	253	26
Deferred revenue	918	174	(58)
Warranty reserve	624	(121)	(954)
Net cash provided by operating activities	21,973	16,369	22,672
Cash flows from investing activities:
Purchases of available-for-sale investments	(8,268)	0	(3,030)
Purchases of held-to-maturity investments	(18,174)	(62,686)	(70,562)
Proceeds from redemptions of available-for-sale investments	0	0	3,000
Proceeds from maturities and redemptions of held-to-maturity investments	42,584	68,604	27,381
Purchases of property and equipment	(7,663)	(6,926)	(3,413)
Cash paid for investment in unconsolidated affiliate	0	(2,800)	0
Net cash provided by (used in) investing activities	8,479	(3,808)	(46,624)
Cash flows from financing activities:
Proceeds from notes payable from municipal agency	147	853	0
Proceeds from the exercise of stock options	615	1,684	915
Tax withholdings related to net share settlements of restricted stock units	(2,211)	(2,013)	(446)
Excess tax benefits from share-based awards	862	2,260	2,096
Repurchases of common stock	(27,328)	0	0
Net cash provided by (used in) financing activities	(27,915)	2,784	2,565
Effect of exchange rate changes on cash and cash equivalents	(165)	269	7
Net increase (decrease) in cash and cash equivalents	2,372	15,614	(21,380)
Cash and cash equivalents at beginning of year	43,471	27,857	49,237
Cash and cash equivalents at end of year	45,843	43,471	27,857
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds	6,161	6,194	6,349
Supplemental disclosure of non-cash flow information:
Change in unrealized gain on investments, net of tax	25	0	0
Transfers of equipment between inventory and property and equipment, net	1,485	1,112	1,797
Net change in capitalized share-based compensation	32	13	61
Common stock withheld for employee taxes in connection with share-based compensation	2,211	2,013	446
Repayment of notes payable by credits from municipal agency	95	22	0
Warrants issued for intangible assets	$ 388	$ 249	$ 0