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Background and Basis of Presentation - Additional Information (Details)
$ in Thousands
1 Months Ended 3 Months Ended
Apr. 30, 2020
USD ($)
Mar. 31, 2020
USD ($)
Segment
Dec. 31, 2019
USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]      
Number of business segments | Segment   1  
Accumulated deficit   $ 433,268 $ 417,624
Cash and cash equivalents   $ 32,692 $ 35,041
Public Stock Offering | Subsequent Event      
Class of Stock [Line Items]      
Gross proceeds from public offering $ 57,600    
Healios | Subsequent Event      
Class of Stock [Line Items]      
Proceeds from exercise of warrant $ 7,000