Annual report pursuant to Section 13 and 15(d)

INCOME TAXES (Details)

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INCOME TAXES (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Deferred tax assets      
Net operating loss carryforwards $ 212,153 $ 297,445  
Orphan drug and research and development credits 51,744 44,348  
Deferred compensation 12,261 21,618  
Capitalized research and development expenses 4,690 1,877  
Other, net 815 3,069  
Total deferred tax assets 281,663 368,357  
Valuation allowance $ (281,663) $ (368,357)  
Reconciliation of the statutory federal income tax rate to the effective tax rate      
Federal statutory tax rate (as a percent) (34.00%) (34.00%) (34.00%)
Federal statutory rate reduction 160.20%    
Valuation allowance (as a percent) (126.50%) 35.00% 31.30%
Stock compensation (as a percent) 5.70% 5.00% 8.30%
Orphan drug and research and development credits (3.60%) (7.30%) (5.60%)
Other, net (as a percent) (1.80%) 1.30%  
Effective tax rate (as a percent) 0.00% 0.00% 0.00%