Assumptions Used to Estimate Grant Date Fair Value Using the Black-Scholes Model (Detail) (USD $)	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2013 March 31, 2012 Offering
Employee Stock Purchase Plan, Fair Value Assumptions, Method Used [Line Items]
Risk-free interest rate	0.27%	0.42%	0.19%
Expected dividend yield	5.29%	5.44%	4.34%
Expected life	1 year	1 year	1 year
Expected stock price volatility	31.26%	40.36%	37.30%
Weighted average fair value of ESPP rights	$ 3.00	$ 2.03	$ 3.27