Changes in Valuation Allowance for Deferred Tax Assets (Detail) - Valuation Allowance of Deferred Tax Assets - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Valuation Allowance [Line Items]
Balance at beginning of year	$ 1,652	$ 2,468	$ 2,418
Increases		325	50
Decreases	(350)	(1,141)
Balance at end of year	$ 1,302	$ 1,652	$ 2,468