STOCK-BASED COMPENSATION - Status of Nonvested Shares and Unrecognized Costs (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unrecognized costs
Unrecognized costs related to all share-based awards outstanding	$ 6.9
Weighted average period for recognition of unrecognized compensation costs	2 years 7 months 6 days
Stock options
Nonvested Shares
Nonvested at the beginning of the period (in shares)	1,167,998
Granted (in shares)	411,956
Vested (in shares)	(343,651)
Forfeited (in shares)	(33,336)
Nonvested at the end of the period (in shares)	1,202,967	1,167,998
Weighted-Average Grant Date Fair Value
Nonvested at the beginning of the period (in dollars per share)	$ 5.39
Granted (in dollars per share)	11.92	$ 6.67	$ 5.90
Vested (in dollars per share)	3.84
Forfeited (in dollars per share)	6.44
Nonvested at the end of the period (in dollars per share)	$ 8.07	$ 5.39