NATURE OF BUSINESS AND BASIS OF PRESENTATION (Details) - USD ($) $ / shares in Units, $ in Thousands					1 Months Ended	9 Months Ended
	Oct. 11, 2018	Oct. 05, 2018	Aug. 09, 2018	Jul. 25, 2017	Nov. 08, 2018	Sep. 30, 2017	Oct. 01, 2018	Sep. 30, 2018	Dec. 31, 2017
Equity Offerings
Common stock, par value								$ 0.001	$ 0.001
Net proceeds						$ 96,255
Common stock shares issued				16,101,970
Accumulated deficit								$ (175,890)	$ (134,371)
Common stock.
Equity Offerings
Shares warrants may purchase				202,020
IPO
Equity Offerings
Issuance of common stock upon IPO, net of underwriters discount and offering costs (in shares)				6,900,000
Share price (in dollars per share)				$ 15.00
Net proceeds				$ 94,000
IPO | Common stock.
Equity Offerings
Common stock, par value				$ 0.001
Underwriter's option
Equity Offerings
Issuance of common stock upon IPO, net of underwriters discount and offering costs (in shares)				900,000
Underwriting discounts and commissions				$ 7,300
Offering costs				$ 2,200
Underwriter's option | Subsequent Event
Equity Offerings
Issuance of common stock upon IPO, net of underwriters discount and offering costs (in shares)		1,125,000
Shelf
Equity Offerings
Share authorized value			$ 250,000
Registration period			3 years
Sales agreement			$ 50,000
Shelf | Subsequent Event
Equity Offerings
Issuance of common stock upon IPO, net of underwriters discount and offering costs (in shares)	8,625,000	7,500,000
Price per share		$ 8.25
Net proceeds	$ 66,400
ATM | Subsequent Event
Equity Offerings
Issuance of common stock upon IPO, net of underwriters discount and offering costs (in shares)					518,135
Net proceeds					$ 4,700
Athyrium | Subsequent Event
Equity Offerings
Shares warrants may purchase							270,835
Athyrium | Term Loan A | Subsequent Event
Equity Offerings
Aggregate principal amount							$ 75,000
Athyrium | Term Loan B | Subsequent Event
Equity Offerings
Aggregate principal amount							$ 35,000