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Inventories - Additional Information (Detail) (USD $)
3 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Mar. 31, 2012
Inventory Disclosure [Line Items]      
Write-down of inventory $ 252,000 $ 156,000  
Demo inventory $ 300,000   $ 400,000
Minimum
     
Inventory Disclosure [Line Items]      
Demo inventory amortization period 1 year    
Maximum
     
Inventory Disclosure [Line Items]      
Demo inventory amortization period 5 years