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)