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COMMON STOCK AND STOCK INCENTIVE PLANS - Dividend Yield, Black-Scholes Assumptions and Unrecognized Compensation Cost (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Black-Scholes option pricing model with the assumptions      
Expected term in years   4 years 9 months 4 years 9 months
Weighted average risk-free interest rate   1.30% 1.50%
Expected dividend rate 0.00% 0.00% 0.00%
Volatility   51.60% 72.70%
Unrecognized compensation cost related to unvested stock options and restricted stock and restricted stock units      
Unrecognized compensation cost $ 0.8 $ 1.8  
Expected weighted-average period of unrecognized cost 1 year 2 months 23 days 1 year 10 months 13 days