UNAUDITED QUARTERLY OPERATING RESULTS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
UNAUDITED QUARTERLY OPERATING RESULTS.
Product revenues, net	$ 1,303	$ 408							$ 1,711
Cost of product revenues	184	29							213
Research and development	3,331	3,254	$ 4,301	$ 4,062	$ 1,531	$ 3,358	$ 1,641	$ 1,445	14,948	$ 7,975	$ 14,959
Selling, general and administrative	25,367	23,567	20,173	11,525	7,905	5,907	2,934	2,186
Total costs and expenses	28,882	26,850	24,474	15,587	9,436	9,265	4,575	3,631	95,793	26,907	17,665
Loss from operations	(27,579)	(26,442)	(24,474)	(15,587)	(9,436)	(9,265)	(4,575)	(3,631)	(94,082)	(26,907)	(17,665)
Other expense, net	20	(2)	(46)	(66)	(89)	(97)	(99)	(63)	(94)	(348)	(252)
Net loss	$ (27,559)	$ (26,444)	$ (24,520)	$ (15,653)	$ (9,525)	$ (9,362)	$ (4,674)	$ (3,694)	$ (94,176)	$ (27,255)	$ (17,917)
Weighted-average number of common shares used in net loss per share - basic					20,558,205	20,531,406	11,791,546	1,001,704
Weighted Average Number of Shares Outstanding, Basic					20,558,205	20,531,406	11,791,546	1,001,704
Shares used in computing net loss per share-diluted (in shares)					20,558,205	20,531,406	11,791,546	7,554,524
Earnings (loss) per share - basic					$ (0.46)	$ (0.46)	$ (0.45)	$ 0.34	$ (3.88)	$ (1.48)	$ (22.72)
Earnings (loss) per share - diluted					$ (0.46)	$ (0.46)	$ (0.45)	$ (0.65)
Weighted-average shares - basic and diluted	27,100,231	23,460,340	23,417,378	23,130,153					24,262,945	13,542,282	933,997
Loss per share - basic and diluted	$ (1.02)	$ (1.13)	$ (1.05)	$ (0.68)					$ (3.88)	$ (1.48)	$ (22.72)