CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $)	9 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities:
Net income	$ 20,761,000	$ 8,385,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	4,448,000	3,725,000
Investment premium amortization, net	638,000	754,000
Net loss on disposals of property and equipment	19,000	10,000
Net loss on foreign exchange translation	174,000	402,000
Share-based compensation expense	5,290,000	4,194,000
Excess tax benefits from share-based awards	(1,826,000)	(717,000)
Provision for deferred income taxes	(253,000)	157,000
Equity in net loss of unconsolidated affiliate	13,000	101,000
Changes in assets and liabilities:
Receivables, net	(5,368,000)	1,703,000
Inventories	(6,321,000)	(1,100,000)
Prepaid expenses and other current assets	(330,000)	(1,142,000)
Other assets	(13,000)	21,000
Accounts payable	5,156,000	108,000
Accrued payroll and related expenses	2,046,000	(380,000)
Accrued taxes	393,000	(559,000)
Other accrued liabilities	323,000	380,000
Deferred rent	71,000	181,000
Deferred revenue	1,297,000	733,000
Warranty reserve	(380,000)	383,000
Net cash provided by operating activities	26,138,000	17,339,000
Cash flows from investing activities:
Purchases of available-for-sale investments	0	(8,268,000)
Purchases of held-to-maturity investments	(18,337,000)	(18,174,000)
Proceeds from maturities and redemptions of held-to-maturity investments	18,261,000	35,337,000
Proceeds from maturities and redemptions of available-for-sale investments	249,000	0
Purchases of property and equipment	(4,334,000)	(5,960,000)
Proceeds from disposal of property and equipment	4,000	0
Net cash (used in) provided by investing activities	(4,157,000)	2,935,000
Cash flows from financing activities:
Proceeds from notes payable from municipal agency	0	147,000
Proceeds from the exercise of stock options	1,593,000	576,000
Tax withholdings related to net share settlements of restricted stock units	(1,584,000)	(2,172,000)
Excess tax benefits from share-based awards	1,826,000	717,000
Repurchases of common stock	0	(27,328,000)
Dividends paid	(22,023,000)	0
Net cash used in financing activities	(20,188,000)	(28,060,000)
Effect of exchange rate changes on cash and cash equivalents	(209,000)	(317,000)
Net increase (decrease) in cash and cash equivalents	1,584,000	(8,103,000)
Cash and cash equivalents at beginning of period	45,843,000	43,471,000
Cash and cash equivalents at end of period	47,427,000	35,368,000
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds	12,206,000	4,809,000
Supplemental disclosure of non-cash flow information:
Change in unrealized gain (loss) on investments, net of tax	21,000	(14,000)
Transfers of equipment between inventory and property and equipment, net	878,000	1,130,000
Net change in capitalized share-based compensation	29,000	68,000
Common stock withheld for employee taxes in connection with share-based compensation	1,584,000	2,172,000
Repayment of notes payable by credits from municipal agency	76,000	70,000
Warrants issued for intangible assets	$ 0	$ 388,000