STOCK-BASED COMPENSATION (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense	$ 11.7	$ 8.3
Payments for the purchase of shares to satisfy the employee income tax withholdings	$ 5.7	$ 13.9
Restricted Stock and Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
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
Shares purchased to satisfy the employee income tax withholdings (in shares)	49,220
Payments for the purchase of shares to satisfy the employee income tax withholdings	$ 4.8
Vested (in shares)	135,853
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
Number of shares of common stock of which unit is convertible (in shares)	1
Vesting period	3 years
Shares purchased to satisfy the employee income tax withholdings (in shares)	9,982
Payments for the purchase of shares to satisfy the employee income tax withholdings	$ 0.9
Vested (in shares)	29,468
Risk-free interest rate	0.15%
Volatility time period	3 years
Expected volatility	31.80%
Correlation to S&P 500 Index time period	3 years
Correlation with S&P index	0.51
Unrecognized compensation expense	$ 40.2
Unrecognized compensation expense, period for recognition	2 years 2 months 12 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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Share-based Compensation Arrangement By Share-based Payment Award, Original Units Granted, Percent

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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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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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