SHARE-BASED AWARDS - EXPENSE (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based expense (net of estimated forfeitures)
Intrinsic value of options exercised	$ 0.7	$ 2.0	$ 9.2
Tax benefit realized upon option exercise	6.8	5.9	3.4
Fair value of stock vested	17.3	15.8	8.6
Non-vested stock and restricted stock units
Share-based expense (net of estimated forfeitures)
Total share-based expense	11.1	9.8	12.2
Non-vested restricted stock units and performance-based equity awards
Share-based expense (net of estimated forfeitures)
Unrecognized compensation cost	$ 11.5
Unrecognized compensation cost, weighted average period for recognition	1 year 8 months 12 days
Stock options
Share-based expense (net of estimated forfeitures)
Total recognized tax benefit		$ (2.2)	$ (2.6)
Unrecognized compensation cost	$ 0.0

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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Unrecognized cost of unvested share-based compensation awards.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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