Period of time related to S&P 500 Index.

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- Definition

The qualified retirement eligibility age for grants awarded in and after 2017.

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The qualified retirement eligibility number of years of service for grants awarded in and after 2017.

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- Definition

Share-based Compensation Arrangement By Share-based Payment Award, Original Units Granted, Percent

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Number of Shares of Common Stock of Which Instrument is Convertible

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Correlation with S&P500

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- Definition

Period of time related to volatility.

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No definition available.

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- Definition

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

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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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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- Definition

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

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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- Definition

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

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- Definition

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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- Definition

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

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- Definition

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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No definition available.

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- Definition

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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- Definition

Number of shares used to settle grantee's tax withholding obligation for award under share-based payment arrangement.

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Number of share options (or share units) exercised during the current period.

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STOCK-BASED COMPENSATION (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
STOCK-BASED COMPENSATION (Details) - USD ($) $ in Millions	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense	$ 4.6	$ 6.3	$ 12.9	$ 11.7
Options exercised (in shares)			10,834
Payments for the purchase of shares to satisfy the employee income tax withholdings (in shares)			$ 14.1	10.4
Stock options
Share-based Compensation Arrangement by Share-based Payment Award
Total intrinsic value of stock options exercised			$ 0.9	$ 22.4
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)			99,358
Payments for the purchase of shares to satisfy the employee income tax withholdings (in shares)			$ 11.7
Number of shares of common stock of which unit is convertible (in shares)	1		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)			268,187
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		1
Vesting period			3 years
Vested (in shares)	48,053		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	$ 30.9		$ 30.9
Unrecognized compensation expense, period for recognition			2 years
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%