Marketable Securities (Parenthetical) (Detail)	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Maximum
Investment [Line Items]
Short-term marketable securities, maturity period	1 year	1 year
Long-term marketable securities, maturity period	2 years	2 years
Minimum
Investment [Line Items]
Long-term marketable securities, maturity period	1 year	1 year