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STOCK-BASED COMPENSATION - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vesting period, minimum | 3 years |  |
Number of shares of common stock that may be issued (in shares) | 1,000,000 |  |
Stock Option Awards [Abstract] |  |  |
Total unrecognized compensation costs | $ 8.9 |  |
Weighted average period for recognition of unrecognized compensation costs | 1 year 9 months 18 days |  |
Restricted Stock Awards |  |  |
Restricted Stock Awards [Abstract] |  |  |
Vested restricted stock withheld for tax withholding obligations (in shares) | 35,514 | 30,712 | 31,688
Vested restricted stock withheld for tax withholding obligations, weighted average price (in dollars per share) | $ 63.83 | $ 57.29 | $ 50.65
Fair value, restricted stock | $ 8.9 | $ 6.3 | $ 6.4
Actual tax benefit realized | $ 3.3 | $ 2.4 | $ 2.4
Restricted Stock Awards | Performance Vesting |  |  |
Restricted Stock Awards [Abstract] |  |  |
Vested (in shares) | 78,825 |  |
Restricted Stock Awards | Performance Vesting | Executive Officers and Key Employees |  |  |
Restricted Stock Awards [Abstract] |  |  |
Granted, weighted average grant date fair value (in dollars per share) |  | $ 45.95 | $ 36.69
Restricted Stock Awards | Time Vesting |  |  |
Restricted Stock Awards [Abstract] |  |  |
Granted (in shares) | 44,090 |  |
Granted, weighted average grant date fair value (in dollars per share) | $ 63.15 |  |
Vested (in shares) | 58,200 |  |
Restricted Stock Awards | Time Vesting | Executive Officers and Key Employees |  |  |
Restricted Stock Awards [Abstract] |  |  |
Granted (in shares) | 33,240 |  |
Granted, weighted average grant date fair value (in dollars per share) | $ 63.05 | 59.40 | 50.90
Restricted Stock Awards | Time Vesting | Non Employee Directors |  |  |
Restricted Stock Awards [Abstract] |  |  |
Granted (in shares) | 10,850 |  |
Granted, weighted average grant date fair value (in dollars per share) | $ 63.45 | $ 63.93 | $ 54.66
Stock Option Awards |  |  |
Stock Option Awards [Abstract] |  |  |
Cash received from the exercise of stock options |  | $ 0.7 | $ 1.5
Intrinsic value of exercised |  | $ 0.7 | $ 0.9

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- Definition Unrecognized cost of unvested share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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