STOCK BASED COMPENSATION - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	May 31, 2015
Stock-based compensation
Unrecognized compensation cost related to outstanding options	$ 18,889		$ 18,889
Shares of common stock authorized for issuance outstanding (in shares)	3,056,954		3,056,954		2,326,801
Employee Stock Purchase Plan, Purchase Price Percentage			85.00%
Issuance for employee stock purchase plan, shares			110,841
Proceeds from issuances of common stock from employee stock purchase plans			$ 1,141
Employee Stock Purchase Plan, Compensation Expense	$ 74	$ 143	$ 288	$ 311
Stock options
Stock-based compensation
Period over which unrecognized compensation cost is expected to be recognized as expense			2 years 8 months 12 days
2014 Stock Incentive Plan
Stock-based compensation
Shares of common stock authorized for issuance (in shares)						2,700,000
Share of common stock remaining available for future grant	1,142,277		1,142,277
Increase in number of authorized shares on the first day of each fiscal year, as a percentage of outstanding common stock (as a percent)			4.00%
Vesting period			4 years
Contractual life			10 years
2014 Stock Incentive Plan | Minimum
Stock-based compensation
Period following termination date vested options are exercisable			1 month
2014 Stock Incentive Plan | Maximum
Stock-based compensation
Period following termination date vested options are exercisable			3 months