OVERVIEW OF BUSINESS AND BASIS OF PRESENTATION (Details)					6 Months Ended
	Feb. 14, 2018 USD ($) shares	Feb. 14, 2018 USD ($) shares	Feb. 13, 2018 USD ($) $ / shares shares	Jan. 26, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($)	Dec. 31, 2017 $ / shares shares	May 31, 2017 shares	Feb. 28, 2017 shares
Debt Instrument [Line Items]
Sale of stock, number of shares issued in transaction (in shares) | shares	421,355	5,821,355
Proceeds from IPO | $	$ 5,500,000	$ 75,700,000
Proceeds from IPO, net | $		66,100,000
Sale of stock, discounts and commissions | $		5,300,000
Issuance costs | $		$ 4,300,000			$ 4,279,000	$ 0
Stock split, conversion ratio					0.25
Proceeds from issuance of common stock, threshold | $				$ 70,000,000.0
Common stock, shares authorized (in shares) | shares				100,000,000	100,000,000		83,000,000	83,000,000
Par value (in usd per share) | $ / shares				$ 0.0001	$ 0.0001		$ 0.0001
Preferred stock, shares authorized (in shares) | shares					10,000,000
Preferred stock, par or stated value per share (in usd per share) | $ / shares					$ 0.0001
Shares authorized (in shares) | shares				25,000,000				96,131,002	82,683,212
Redeemable convertible preferred stock, par value (in usd per share) | $ / shares				$ 0.0001
IPO
Debt Instrument [Line Items]
Sale of stock, number of shares issued in transaction (in shares) | shares			5,400,000
Sale of stock, price per share (in usd per share) | $ / shares			$ 13.00
Proceeds from IPO | $			$ 70,200,000
Over-Allotment Option
Debt Instrument [Line Items]
Sale of stock, number of shares issued in transaction (in shares) | shares	810,000