STOCK-BASED COMPENSATION - Summary of Activity under Company's Stock Option Plans (Details) - $ / shares shares in Thousands			3 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Apr. 30, 2017	Apr. 30, 2016
STOCK-BASED COMPENSATION
Shares, Outstanding, Beginning balance			707	1,064
Shares, Granted			105	75
Shares, Exercised			(27)	(22)
Shares, Outstanding, Ending balance	707	1,064	785	1,117
Shares, Exercisable			485	842
Weighted Average Exercise Price, Outstanding, Beginning balance			$ 39.04	$ 26.38
Weighted Average Exercise Price, Granted			64.25	33.85
Weighted Average Exercise Price, Exercised			31.53	18.80
Weighted Average Exercise Price, Outstanding, Ending balance	$ 39.04	$ 26.38	42.68	27.03
Weighted Average Exercise Price, Exercisable			$ 28.17	$ 24.36
Weighted Average Remaining Term, Outstanding	7 years 9 months 26 days	6 years 4 months 10 days	7 years 11 months 9 days	6 years 11 months 1 day
Weighted Average Remaining Term, Exercisable			6 years 9 months 29 days	6 years 5 months 5 days
Weighted Average Fair Value, Outstanding	$ 10.22	$ 6.91	$ 11.29	$ 7.08
Weighted Average Fair Value, Exercisable			$ 7.51	$ 6.41