COMPUTATION OF EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net income	$ 19,953	$ 20,474	$ 38,781	$ 40,861
Income allocated to participating securities, basic	(597)		(1,169)
Net income attributable to common shareholders, basic	$ 19,356	$ 20,474	$ 37,612	$ 40,861
Denominator:
Weighted average common shares-basic	32,570	32,281	32,538	32,269
Basic earnings per common share (in dollars per share)	$ 0.59	$ 0.63	$ 1.16	$ 1.27
Diluted earnings per common share:
Net effect of reallocating undistributed earnings of unvested shareholders	3		15
Net income attributable to common shareholders, diluted	$ 19,359	$ 20,474	$ 37,627	$ 40,861
Earnings per common share:
Dilutive effect of employee equity incentive plans	239	445	573	596
Weighted average common shares-diluted	32,809	32,726	33,111	32,865
Diluted earnings per common share (in dollars per share)	$ 0.59	$ 0.63	$ 1.14	$ 1.24
Potentially dilutive securities excluded from diluted earnings per common share because their effect is anti-dilutive	1,389	543	959	634