GENERAL ORGANIZATION, BUSINESS AND LIQUIDITY (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended								12 Months Ended
	Jan. 31, 2018	Sep. 25, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Income (Loss) Attributable to Parent, Total			$ (25,854)	$ (22,149)	$ (23,377)	$ (20,684)	$ (15,689)	$ (68,212)	$ (11,563)	$ (6,884)	$ (92,064)	$ (52,894)	$ (27,660)
Cash and Cash Equivalents, at Carrying Value			$ 145,373				$ 106,717				145,373	106,717	33,587	$ 44,909
Stock Issued During Period, Shares, New Issues		8,846,154
Proceeds from Issuance of Common Stock		$ 53,700									53,662	95,685	68,307
Shares Issued, Price Per Share		$ 6.50
Stock Issued During Period, Value, New Issues											53,662		68,307
Net Cash Provided by (Used in) Operating Activities											$ (78,709)	$ (32,668)	$ (18,381)
IPO [Member] | Subsequent Event [Member] | Underwriting Options [Member]
Stock Issued During Period, Shares, New Issues	15,000,000
Proceeds from Issuance of Common Stock	$ 161,700
Shares Issued, Price Per Share	$ 11.50
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	1,956,521
Stock Issued During Period, Value, New Issues	$ 172,500