STOCK BASED COMPENSATION - Summary of Assumptions (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Principal assumptions used in applying the Black-Scholes option pricing model for the awards
Weighted-average expected life of option	3 years 6 months	3 years 6 months	5 years
Weighted-average grant date fair value (in dollars per share)	$ 1.90	$ 2.99	$ 2.36
Risk-free interest rate, low end of range (as a percent)	2.67%	1.46%	1.13%
Risk-free interest rate, high end of range (as a percent)	2.89%	1.60%	1.21%
Volatility factor of the expected market price of common stock, low end of range (as a percent)	63.00%		74.00%
Volatility factor of the expected market price of common stock, high end of range (as a percent)	64.00%
Additional disclosures
Fair value of awards vesting in the period	$ 0.7	$ 1.3	$ 1.3
Unrecognized compensation expense on non-vested stock options (in dollars)	$ 0.4	$ 0.7	$ 1.4
Non-vested stock options outstanding (in shares)	0.7	1.5	2.5
Weighted-average period of recognition	1 year 4 months 24 days	1 year 3 months 18 days	1 year 7 months 6 days
Stock option expense	$ 0.3	$ 1.3	$ 1.0
Minimum
Principal assumptions used in applying the Black-Scholes option pricing model for the awards
Dividend yield (as a percent)	0.36%	0.31%	0.24%
Maximum
Principal assumptions used in applying the Black-Scholes option pricing model for the awards
Dividend yield (as a percent)	0.53%	0.36%	0.27%

Aggregate number of option awards made to employees under a stock option plan or plans, that have yet to vest.

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- Definition

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.

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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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Unrecognized cost of unvested options awarded to employees as compensation.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the maximum 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 estimated measure of the minimum 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 maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

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

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

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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