SHARE-BASED COMPENSATION PLANS - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning of period (in shares)	879,000
Granted (in shares)	121,000
Exercised (in shares)	(182,000)
Forfeited or canceled (in shares)	(11,000)
Outstanding, end of period (in shares)	807,000	879,000
Stock options, exercisable (in shares)	499,000
Stock options, expected to vest (in shares)	308,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding, beginning of period (in dollars per share)	$ 63.44
Granted (in dollars per share)	129.60
Exercised (in dollars per share)	51.50
Forfeited or canceled (in dollars per share)	75.59
Outstanding, end of period (in dollars per share)	75.87	$ 63.44
Weighted average exercise price, exercisable (in dollars per share)	58.27
Weighted average exercise price, expected to vest (in dollars per share)	$ 104.39
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted average remaining contractual term, outstanding	6 years 2 months 12 days
Aggregate intrinsic value, outstanding	$ 54,078
Weighted average remaining contractual term, exercisable	5 years 1 month 6 days
Aggregate intrinsic value, exercisable	$ 42,184
Weighted average remaining contractual term, expected to vest	8 years 1 month 6 days
Aggregate intrinsic value, expected to vest	$ 11,836
Share-based Payment Arrangement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised	19,077	$ 20,711	$ 30,345
Cash received from exercise of options	9,350	13,193	19,247
Tax benefit from exercise of options	3,629	4,449	7,503
Fair value of options vested	$ 3,765	$ 4,506	$ 5,008