STOCK-BASED COMPENSATION - Summary of Activity under Company's Stock Option Plans (Details) - $ / shares shares in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014
STOCK-BASED COMPENSATION
Shares, Outstanding, Beginning balance	1,064	876	916
Shares, Granted	270	300	306
Shares, Exercised	(622)	(106)	(346)
Shares, Forfeited	(5)	(6)
Shares, Outstanding, Ending balance	707	1,064	876	916
Shares, Exercisable	437
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 26.38	$ 22.34	$ 17.36
Weighted Average Exercise Price, Granted	57.88	34.70	21.09
Weighted Average Exercise Price, Exercised	25.57	17.10	15.61
Weighted Average Exercise Price, Forfeited	36.73	17.33
Weighted Average Exercise Price, Outstanding, Ending balance	39.04	$ 26.38	$ 22.34	$ 17.36
Weighted Average Exercise Price, Exercisable	$ 27.40
Weighted Average Remaining Term (Years), Outstanding	7 years 9 months 26 days	6 years 4 months 10 days	7 years 29 days	6 years 15 days
Weighted Average Remaining Term (Years), Exercisable	6 years 8 months 5 days
Weighted Average Fair Value, Outstanding	$ 10.22	$ 6.91	$ 6.01	$ 5.58
Weighted Average Fair Value, Exercisable	$ 7.31