INCOME TAXES (Details) (USD $)	3 Months Ended								12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Current [Abstract]
Federal									$ 14,575,000	$ 5,552,000	$ 5,940,000
State									1,488,000	584,000	961,000
Foreign									174,000	267,000	46,000
Total current income tax provision									16,237,000	6,403,000	6,947,000
Deferred [Abstract]
Federal									(1,219,000)	790,000	1,547,000
State									(88,000)	(117,000)	540,000
Total deferred income tax provision									(1,307,000)	673,000	2,087,000
Total income tax provision	2,223,000	2,996,000	8,012,000	1,699,000	2,184,000	1,696,000	1,918,000	1,278,000	14,930,000	7,076,000	9,034,000
Income before income taxes [Abstract]
United States									41,743,000	19,403,000	23,335,000
Foreign									646,000	764,000	236,000
Income before tax provision									42,389,000	20,167,000	23,571,000
Federal statutory income tax rate (in hundredths)									35.00%
Income Tax Provision Reconciliation [Abstract]
Income taxes at federal income tax rate									14,836,000	7,059,000	8,250,000
State income taxes, net of federal benefits									1,123,000	455,000	1,275,000
Non-deductible compensation									56,000	159,000	89,000
Research and development tax credits									(541,000)	(254,000)	(385,000)
Tax-exempt interest income									(32,000)	(65,000)	(52,000)
Qualified production activities income benefit									(525,000)	(306,000)	(258,000)
Other									13,000	28,000	115,000
Total income tax provision	2,223,000	2,996,000	8,012,000	1,699,000	2,184,000	1,696,000	1,918,000	1,278,000	14,930,000	7,076,000	9,034,000
Excess tax benefits from share-based awards and other tax adjustments									2,683,000	842,000	2,215,000
Cumulative foreign earnings upon which U.S. income taxes has not been provided	619,000								619,000
U.S. tax liability if earnings were repatriated	247,000								247,000
Breakdown Between Current and Non-current Deferred Tax Assets (Liabilities) [Abstract]
Deferred tax assets, current	4,589,000				4,151,000				4,589,000	4,151,000
Deferred tax assets, non-current	643,000				0				643,000	0
Deferred tax liabilities, non-current	0				(199,000)				0	(199,000)
Total net deferred tax assets	5,232,000				3,952,000				5,232,000	3,952,000
Deferred tax assets:
Research and development tax credit carryforwards	475,000				376,000				475,000	376,000
Capitalized research and development	167,000				200,000				167,000	200,000
Inventory reserves	601,000				442,000				601,000	442,000
Deferred revenue from extended maintenance agreements and warranty reserves	2,399,000				2,100,000				2,399,000	2,100,000
Accrued payroll and other accrued expenses	1,266,000				1,145,000				1,266,000	1,145,000
Share-based compensation	2,145,000				1,658,000				2,145,000	1,658,000
Alternative minimum tax credits	24,000				24,000				24,000	24,000
Tax on deferred intercompany profit	1,120,000				896,000				1,120,000	896,000
Other	416,000				477,000				416,000	477,000
Total deferred tax assets	8,613,000				7,318,000				8,613,000	7,318,000
Deferred tax liabilities:
Depreciation	(3,257,000)				(3,274,000)				(3,257,000)	(3,274,000)
Other	(124,000)				(92,000)				(124,000)	(92,000)
Total deferred tax liabilities	(3,381,000)				(3,366,000)				(3,381,000)	(3,366,000)
Net deferred tax assets	5,232,000				3,952,000				5,232,000	3,952,000
Valuation allowance	0				0				0	0	0
Minimum [Member]
Income Tax Contingency [Line Items]
Open Tax Year									1997
Maximum [Member]
Income Tax Contingency [Line Items]
Open Tax Year									2013
Federal [Member]
Income Tax Contingency [Line Items]
Statute of limitations									3 years
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0								0
Federal [Member] | Minimum [Member]
Income Tax Contingency [Line Items]
Open Tax Year									2010
Federal [Member] | Maximum [Member]
Income Tax Contingency [Line Items]
Open Tax Year									2013
State of California [Member]
Income Tax Contingency [Line Items]
Statute of limitations									4 years
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0								0
State of California [Member] | Research and Development Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax credit carryforward with indefinite life	$ 730,000								$ 730,000
State of California [Member] | Minimum [Member]
Income Tax Contingency [Line Items]
Open Tax Year									2009
State of California [Member] | Maximum [Member]
Income Tax Contingency [Line Items]
Open Tax Year									2013
Germany [Member] | Minimum [Member]
Income Tax Contingency [Line Items]
Open Tax Year									2011
Germany [Member] | Maximum [Member]
Income Tax Contingency [Line Items]
Open Tax Year									2013