Assumptions Used to Estimate Grant Date Fair Value Using the Black-Scholes Model (Detail) (USD $)	12 Months Ended
Mar. 31, 2011 Year	Mar. 31, 2010 Year	Dec. 31, 2011 March 31, 2012 Offering Year
Employee Stock Purchase Plan, Fair Value Assumptions, Method Used [Line Items]
Risk-free interest rate	0.42%	0.58%	0.27%
Expected dividend yield	5.44%	0.00%	5.29%
Expected life	1.0	1.0	1.0
Expected stock price volatility	40.36%	74.79%	31.26%
Weighted average fair value of ESPP rights	$ 2.03	$ 2.28	$ 3.00

The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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