XML 31 R20.htm IDEA: XBRL DOCUMENT v3.19.2
Prepaid Expenses and Other Current Assets (Tables)
6 Months Ended
Jun. 30, 2019
Prepaid Expenses And Other Current Assets [Abstract]  
Schedule of prepaid expenses and other current assets
    December 31,     June 30,  
    2018     2019  
Research and development tax credit receivable   $ 1,148     $ 1,710  
Prepayments and VAT receivable     899       1,045  
Other current assets     236       236  
    $ 2,283     $ 2,991