Sales of Investment Securities Available For Sale (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Mar. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales & calls	$ 12,780	[1]	$ 338,224	[1]	$ 385,924	[1]
Gross gains	91		6,618		8,661
Gross losses	(338)		(39)
Net gain/(loss) on sales & calls	$ (247)	[1]	$ 6,579	[1]	$ 8,661	[1]

[1] Includes proceeds from calls by the issuers of investment securities totaling $518,000 during the year ended March 31, 2013 resulting in a gain on calls of $18,000.