Weighted Average Assumptions Used to Calculate Fair Value of Options Granted (Detail)	3 Months Ended		9 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Risk-free interest rate	0.63%	0.92%	0.77%	1.49%
Expected option life (years)	4 years 2 months 23 days	5 years 1 month 2 days	4 years 3 months 26 days	5 years 2 months 23 days
Expected volatility	58.10%	55.10%	56.40%	52.70%