COMPUTATION OF EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 19,517	$ 22,221	$ 20,474	$ 20,387	$ 12,980	$ 16,288	$ 17,896	$ 21,228	$ 82,599	$ 68,392	$ 112,301
Earnings Per Share, Basic and Diluted
Weighted average common shares-basic									32,279	34,127	41,723
Dilutive effect of employee equity incentive plans									684	811	920
Weighted average common shares-diluted									32,963	34,938	42,643
Basic net income per common share (in dollars per share)	$ 0.60	$ 0.69	$ 0.63	$ 0.63	$ 0.40	$ 0.50	$ 0.53	$ 0.56	$ 2.56	$ 2.00	$ 2.69
Diluted net income per common share (in dollars per share)	$ 0.59	$ 0.68	$ 0.63	$ 0.62	$ 0.39	$ 0.49	$ 0.52	$ 0.55	$ 2.51	$ 1.96	$ 2.63
Potentially dilutive securities excluded from diluted earnings per share because their effect is anti-dilutive									574	326	442