Quarterly report pursuant to Section 13 or 15(d)

CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Additional Information (Details)

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CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Additional Information (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Cash and Cash Equivalents [Line Items]          
Cash and cash equivalents $ 535,253 $ 104,355 $ 535,253 $ 104,355 $ 312,799
Interest income 7 36 25 503  
Restricted cash, noncurrent 2,177   2,177   12,077
Restricted cash 2,177 30,484 2,177 30,484  
Government grant awarded         76,400
Proceeds of Government Grant       74,200  
CARES Act grant 0 $ 51,646 0 $ 64,923  
Line of Credit | Amended 1st Credit Facility          
Cash and Cash Equivalents [Line Items]          
Restricted cash, noncurrent         10,000
Credit facility, borrowing availability         175,400
Money market funds          
Cash and Cash Equivalents [Line Items]          
Cash and cash equivalents 408,100   408,100   $ 103,500
Cash Equivalents          
Cash and Cash Equivalents [Line Items]          
Interest income $ 7   $ 25