Inventories - Additional Information (Detail) (USD $)	9 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2012
Inventory Disclosure [Line Items]
Write-down of inventory	$ 891,000	$ 1,092,000
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