Annual report pursuant to Section 13 and 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Contingencies (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Contingencies (Details)
$ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
Dec. 31, 2017
USD ($)
Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]    
Number of future milestone events probable of achievement | Milestone   1
Consulting agreement, expense recognized $ 1.5  
Minimum    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]    
Consulting agreement, contingent liability   $ 1.5
Maximum    
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]    
Consulting agreement, contingent liability   $ 4.0