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, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share [Abstract]
Net income	$ 25,924	$ 27,521	$ 49,487	$ 54,252
Earnings Per Share, Basic and Diluted [Abstract]
Weighted average common shares-basic	41,482	44,556	41,571	45,664
Dilutive effect of employee equity incentive plans	921	1,161	950	1,286
Weighted average common shares-diluted	42,403	45,717	42,521	46,950
Basic earnings per common share	$ 0.62	$ 0.62	$ 1.19	$ 1.19
Diluted earnings per common share	$ 0.61	$ 0.60	$ 1.16	$ 1.16
Potentially dilutive securities excluded from diluted earnings per common share because their effect is anti-dilutive	1,061	1,946	1,081	1,781