COMPUTATION OF EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 12,980	$ 16,288	$ 17,896	$ 21,228	$ 25,824	$ 30,384	$ 27,421	$ 28,672	$ 68,392	$ 112,301	$ 112,417
Earnings Per Share, Basic and Diluted
Weighted average common shares-basic									34,127	41,723	42,452
Dilutive effect of employee equity incentive plans									811	920	912
Weighted average common shares-diluted									34,938	42,643	43,364
Basic net income per common share (in dollars per share)	$ 0.40	$ 0.50	$ 0.53	$ 0.56	$ 0.62	$ 0.73	$ 0.66	$ 0.69	$ 2.00	$ 2.69	$ 2.65
Diluted net income per common share (in dollars per share)	$ 0.39	$ 0.49	$ 0.52	$ 0.55	$ 0.61	$ 0.71	$ 0.65	$ 0.68	$ 1.96	$ 2.63	$ 2.59
Potentially dilutive securities excluded from diluted earnings per share because their effect is anti-dilutive									326	442	202