Weighted Average Assumptions Used to Calculate Fair Value of Options Granted (Detail)	3 Months Ended		6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Risk-free interest rate	0.68%	0.94%	0.77%	1.72%
Expected option life (years)	4 years 2 months 12 days	5 years 2 months 16 days	4 years 3 months 26 days	5 years 3 months 15 days
Expected volatility	56.20%	53.10%	56.30%	51.80%