CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $)	6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities:
Net income	$ 15,773,000	$ 5,535,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	2,916,000	2,435,000
Investment premium amortization, net	448,000	503,000
Net loss on disposals of property and equipment	20,000	8,000
Net loss on foreign exchange translation	292,000	141,000
Share-based compensation expense	3,511,000	2,682,000
Excess tax benefits from share-based awards	(1,145,000)	(486,000)
Provision for deferred income taxes	(303,000)	374,000
Equity in net loss of unconsolidated affiliate	34,000	72,000
Changes in assets and liabilities:
Receivables, net	(17,691,000)	288,000
Inventories	(3,121,000)	41,000
Prepaid expenses and other current assets	3,988,000	(1,144,000)
Other assets	6,000	20,000
Accounts payable	1,824,000	839,000
Accrued payroll and related expenses	1,736,000	744,000
Accrued taxes	3,700,000	(316,000)
Other accrued liabilities	1,118,000	96,000
Deferred rent	50,000	114,000
Deferred revenue	585,000	518,000
Warranty reserve	(366,000)	214,000
Net cash provided by operating activities	13,375,000	12,678,000
Cash flows from investing activities:
Purchases of held-to-maturity investments	(13,961,000)	(18,174,000)
Proceeds from maturities and redemptions of held-to-maturity investments	11,951,000	33,141,000
Proceeds from maturities and redemptions of available-for-sale investments	249,000	0
Purchases of property and equipment	(2,945,000)	(4,777,000)
Net cash (used in) provided by investing activities	(4,706,000)	10,190,000
Cash flows from financing activities:
Proceeds from notes payable from municipal agency	0	147,000
Proceeds from the exercise of stock options	261,000	430,000
Tax withholdings related to net share settlements of restricted stock units	(1,495,000)	(2,019,000)
Repurchases of common stock	0	(27,328,000)
Excess tax benefits from share-based awards	1,145,000	486,000
Net cash used in financing activities	(89,000)	(28,284,000)
Effect of exchange rate changes on cash and cash equivalents	(314,000)	(61,000)
Net increase (decrease) in cash and cash equivalents	8,266,000	(5,477,000)
Cash and cash equivalents at beginning of period	45,843,000	43,471,000
Cash and cash equivalents at end of period	54,109,000	37,994,000
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds	3,308,000	2,796,000
Supplemental disclosure of non-cash flow information:
Change in unrealized gain (loss) on investments, net of tax	22,000	0
Transfers of equipment between inventory and property and equipment, net	693,000	645,000
Net change in capitalized share-based compensation	35,000	(19,000)
Common stock withheld for employee taxes in connection with share-based compensation	1,495,000	2,019,000
Repayment of notes payable by credits from municipal agency	$ 50,000	$ 44,000