Weighted Average Assumptions Used to Calculate Fair Value of Options Granted (Detail)	3 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Risk-free interest rate	0.85%	0.78%
Expected option life (years)	4 years 3 months 4 days	4 years 3 months 29 days
Expected volatility	51.90%	56.30%