CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income	$ 8,385	$ 11,164
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	3,725	3,326
Investment premium amortization, net	754	343
Net loss on disposals of property and equipment	10	5
Net loss (gain) on foreign exchange translation	402	(59)
Share-based compensation expense	4,194	3,547
Excess tax benefits from share-based awards	(717)	(1,908)
Provision for deferred income taxes	157	980
Equity in net loss of unconsolidated affiliate	101	0
Changes in assets and liabilities:
Receivables, net	1,703	(1,576)
Inventories	(1,100)	(1,250)
Prepaid expenses and other current assets	(1,142)	(1,983)
Other assets	21	(36)
Accounts payable	108	(1,804)
Accrued payroll and related expenses	(380)	(452)
Accrued taxes	(559)	294
Other accrued liabilities	380	152
Deferred rent	181	212
Deferred revenue	733	205
Warranty reserve	383	(476)
Net cash provided by operating activities	17,339	10,684
Cash flows from investing activities:
Purchases of available-for-sale investments	(8,268)	0
Purchases of held-to-maturity investments	(18,174)	(49,547)
Proceeds from maturities and redemptions of held-to-maturity investments	35,337	56,861
Purchases of property and equipment	(5,960)	(3,559)
Net cash provided by investing activities	2,935	3,755
Cash flows from financing activities:
Proceeds from notes payable from municipal agency	147	0
Proceeds from the exercise of stock options	576	1,288
Tax withholdings related to net share settlements of restricted stock units	(2,172)	(2,004)
Repurchases of common stock	(27,328)	0
Excess tax benefits from share-based awards	717	1,908
Net cash (used in) provided by financing activities	(28,060)	1,192
Effect of exchange rate changes on cash and cash equivalents	(317)	68
Net (decrease) increase in cash and cash equivalents	(8,103)	15,699
Cash and cash equivalents at beginning of period	43,471	27,857
Cash and cash equivalents at end of period	35,368	43,556
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds	4,809	5,849
Supplemental disclosure of non-cash flow information:
Change in unrealized loss on investments, net of tax	(14)	0
Transfers of equipment between inventory and property and equipment, net	1,130	746
Net change in capitalized share-based compensation	68	17
Common stock withheld for employee taxes in connection with share-based compensation	2,172	2,004
Repayment of notes payable by credits from municipal agency	70	0
Warrants issued for intangible assets	$ 388	$ 0