Calculations of Basic and Diluted Net Income Per Share and Potential Common Shares (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share Disclosure [Line Items]
Net income	$ 9,910	$ 7,051	$ 14,918	$ 9,450
Weighted average common shares outstanding	41,695	42,258	41,718	42,433
Basic net income per share	$ 0.24	$ 0.17	$ 0.36	$ 0.22
Weighted average stock options	134	128	135	163
Weighted average restricted stock units	515	334	547	465
Diluted weighted average shares	42,344	42,720	42,400	43,061
Diluted net income per share	$ 0.23	$ 0.17	$ 0.35	$ 0.22