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Summary of Significant Accounting Policies - Inventory (Detail) - USD ($)
$ in Thousands
12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Mar. 31, 2016
Inventory [Line Items]      
Inventory write-down $ 434 $ 1,615 $ 2,713
Inventory Valuation Reserve      
Inventory [Line Items]      
Benefits recorded for the usage of inventories previously reserved $ (700) $ (1,400) $ (5,000)