COMPUTATION OF EARNINGS PER COMMON SHARE (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]
Net income	$ 23,138	$ 25,924	$ 50,091	$ 49,487
Earnings Per Share, Basic and Diluted [Abstract]
Weighted average common shares-basic	42,810	41,482	42,751	41,571
Dilutive effect of employee equity incentive plans	787	921	916	950
Weighted average common shares-diluted	43,597	42,403	43,667	42,521
Basic earnings per common share	$ 0.54	$ 0.62	$ 1.17	$ 1.19
Diluted earnings per common share	$ 0.53	$ 0.61	$ 1.15	$ 1.16
Potentially dilutive securities excluded from diluted earnings per common share because their effect is anti-dilutive	183	1,061	162	1,081