STOCK-BASED COMPENSATION (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense	$ 8.3	$ 5.4
Options exercised (in shares)	1,510
Payments for the purchase of shares to satisfy the employee income tax withholdings (in shares)	$ 13.9	10.0
Stock options
Share-based Compensation Arrangement by Share-based Payment Award
Total intrinsic value of stock options exercised	$ 0.2	$ 20.7
Restricted Stock and Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Shares purchased to satisfy the employee income tax withholdings (in shares)	97,321
Payments for the purchase of shares to satisfy the employee income tax withholdings (in shares)	$ 11.5
Number of shares of common stock of which unit is convertible (in shares)	1
Vesting period	3 years
Qualified retirement eligibility age for grants awarded in and after 2017	55 years
Qualified retirement eligibility number of years of service for grants awarded in and after 2017	10 years
Vested (in shares)	246,850
Restricted Stock and Restricted Stock Units \| Director
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period	1 year
Performance-Based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Shares purchased to satisfy the employee income tax withholdings (in shares)	19,456
Payments for the purchase of shares to satisfy the employee income tax withholdings (in shares)	$ 2.4
Number of shares of common stock of which unit is convertible (in shares)	1
Vesting period	3 years
Vested (in shares)	48,053
Risk-free interest rate	1.36%
Volatility time period	3 years
Expected volatility	21.00%
Correlation to S&P 500 Index time period	3 years
Correlation with S&P index	0.25%
Unrecognized compensation expense	$ 34.1
Unrecognized compensation expense, period for recognition	2 years 3 months 18 days
Performance-Based Restricted Stock Units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Units ultimately expected to be awarded	0.00%
Performance-Based Restricted Stock Units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Units ultimately expected to be awarded	200.00%

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cash outflow to satisfy grantee's tax withholding obligation for award under share-based payment 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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