STOCK-BASED COMPENSATION - Summary of Activity under Company's Stock Option Plans (Details) - $ / shares shares in Thousands			3 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Apr. 30, 2018	Apr. 30, 2017
STOCK-BASED COMPENSATION
Shares, Outstanding, Beginning balance			889	707
Shares, Granted			97	105
Shares, Exercised				(27)
Shares, Outstanding, Ending balance	889	707	986	785
Shares, Exercisable			692	485
Weighted Average Exercise Price, Outstanding, Beginning balance			$ 44.83	$ 39.04
Weighted Average Exercise Price, Granted			37.60	64.25
Weighted Average Exercise Price, Exercised				31.53
Weighted Average Exercise Price, Outstanding, Ending balance	$ 44.83	$ 39.04	44.12	42.68
Weighted Average Exercise Price, Exercisable			$ 44.01	$ 28.17
Weighted Average Remaining Term (Years), Outstanding	7 years 10 months 28 days	7 years 9 months 26 days	7 years 10 months 24 days	7 years 11 months 9 days
Weighted Average Remaining Term (Years), Exercisable			7 years 1 month 10 days	6 years 9 months 29 days
Weighted Average Fair Value, Outstanding	$ 11.74	$ 10.22	$ 11.44	$ 11.29
Weighted Average Fair Value, Exercisable			$ 11.65	$ 7.51