CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net income	$ 7,225	$ 15,773
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	3,584	2,916
Investment premium amortization, net	322	448
Net loss on disposals of property and equipment	6	20
Net (gain) loss on foreign exchange translation	(406)	292
Share-based compensation expense	4,102	3,511
Excess tax benefits from share-based awards	(1,729)	(1,145)
Provision for deferred income taxes	(428)	(303)
Equity in net (income) loss of unconsolidated affiliate	(16)	34
Changes in assets and liabilities:
Receivables, net	4,962	(17,691)
Inventories	(1,174)	(3,121)
Prepaid expenses and other current assets	(699)	3,988
Other assets	13	6
Accounts payable	(1,126)	1,824
Accrued payroll and related expenses	(769)	1,736
Accrued taxes	(17)	3,700
Other accrued liabilities	(460)	1,118
Deferred rent	22	50
Deferred revenue	535	585
Warranty reserve	229	(366)
Net cash provided by operating activities	14,176	13,375
Cash flows from investing activities:
Purchases of held-to-maturity investments	(8,036)	(13,961)
Proceeds from maturities and redemptions of held-to-maturity investments	15,113	11,951
Proceeds from maturities and redemptions of available-for-sale investments	525	249
Purchases of property and equipment	(2,761)	(2,945)
Proceeds from disposals of property and equipment	9	0
Net cash provided by (used in) investing activities	4,850	(4,706)
Cash flows from financing activities:
Proceeds from the exercise of stock options	26	261
Tax withholdings related to net share settlements of restricted stock units	(4,591)	(1,495)
Excess tax benefits from share-based awards	1,729	1,145
Net cash used in financing activities	(2,836)	(89)
Effect of exchange rate changes on cash and cash equivalents	346	(314)
Net increase in cash and cash equivalents	16,536	8,266
Cash and cash equivalents at beginning of period	54,910	45,843
Cash and cash equivalents at end of period	71,446	54,109
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds	4,006	3,308
Supplemental disclosure of non-cash flow information:
Change in unrealized gain (loss) on investments, net of tax	(8)	22
Transfers of equipment between inventory and property and equipment, net	618	693
Net change in capitalized share-based compensation	26	35
Common stock withheld for employee taxes in connection with share-based compensation	4,591	1,495
Repayment of notes payable by credits from municipal agency	$ 50	$ 50