(LOSS) INCOME PER COMMON SHARE - Shares excluded from the computation of weighted average diluted shares outstanding (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Anti-dilutive securities excluded
Anti-dilutive securities excluded (in shares)	6,439,954	4,045,083	1,833,816
Service-based and Performance-based stock options
Anti-dilutive securities excluded
Anti-dilutive securities excluded (in shares)	4,147,027	3,242,919	1,542,064
Performance-based stock options
Anti-dilutive securities excluded
Anti-dilutive securities excluded (in shares)	574,138	770,503	291,277
Service-based RSUs
Anti-dilutive securities excluded
Anti-dilutive securities excluded (in shares)	325,469	21,623
Performance-based RSUs
Anti-dilutive securities excluded
Anti-dilutive securities excluded (in shares)	1,372,927
RSAs
Anti-dilutive securities excluded
Anti-dilutive securities excluded (in shares)	20,393	10,038	475