STOCK-BASED COMPENSATION, SUMMARY OF OPTION ACTIVITY - (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017
Summary of option activity - Shares
Outstanding at the beginning of year (in shares)		3,193,785
Granted (in shares)		1,439,463
Forfeited (in shares)		(570,863)
Exercised (in shares)		(89,387)
Outstanding at the end of period (in shares)	3,972,998	3,972,998
Vested at the end of period (in shares)		2,146,415
Summary of option activity - Weighted Average Exercise Price
Outstanding at the beginning of year (in dollars per shares)		$ 7.52
Granted (in dollars per shares)		3.94
Forfeited (in dollars per shares)		6.54
Exercised (in dollars per shares)		0.29
Outstanding at the end of period (in dollars per shares)	$ 6.53	6.53
Vested at the end of period (in dollars per share)	$ 7.86	$ 7.86
Option activity disclosures
Weighted Average Remaining Contractual Term - Outstanding		7 years 5 months 23 days
Weighted Average Remaining Contractual Term - Vested		6 years 2 months 12 days
Aggregate Intrinsic Value - Outstanding (in dollars)	$ 53,894	$ 53,894
Aggregate Intrinsic Value - Vested (in dollars)	53,894	$ 53,894
Stock Option
Weighted average grant-date fair value of options granted		$ 3.04
Total fair value of options vested	1,100	$ 3,100
Total unrecognized compensation expense	$ 6,500	$ 6,500
Period for unrecognized compensation expense is estimated to be recognized		2 years 6 months 11 days