Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE MEASUREMENTS - Assets measured on recurring basis (Details)

v3.21.1
FAIR VALUE MEASUREMENTS - Assets measured on recurring basis (Details) - USD ($)
 3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Assets      
Level 1 to Level 2 transfer $ 0 $ 0  
Level 2 to Level 1 transfer 0 0  
Transfer into Level 3 0 0  
Transfer out of Level 3 0 $ 0  
Movement in Level 3 liabilities measured at fair value      
Balance at beginning of period 93,328,000    
Changes in fair value 56,576,000    
Exercise of private placement warrants (149,904,000)    
Level 3      
Movement in Level 3 assets measured at fair value      
Balance at beginning of year 3,000,000    
Changes in fair value 25,000    
Balance at end of year 3,025,000    
Recurring      
Assets      
Total assets 571,961,000   $ 597,753,000
Total liabilities     93,328,000
Recurring | Private Placement Warrants      
Assets      
Total liabilities     93,328,000
Recurring | Money market funds      
Assets      
Total assets 413,089,000   407,512,000
Recurring | Commercial paper      
Assets      
Total assets 89,835,000   119,285,000
Recurring | Corporate bonds      
Assets      
Total assets 61,012,000   47,959,000
Recurring | U.S Treasury securities      
Assets      
Total assets 5,000,000   19,997,000
Recurring | Other investments      
Assets      
Total assets 3,025,000   3,000,000
Recurring | Level 1      
Assets      
Total assets 418,089,000   427,509,000
Recurring | Level 1 | Money market funds      
Assets      
Total assets 413,089,000   407,512,000
Recurring | Level 1 | U.S Treasury securities      
Assets      
Total assets 5,000,000   19,997,000
Recurring | Level 2      
Assets      
Total assets 150,847,000   167,244,000
Recurring | Level 2 | Commercial paper      
Assets      
Total assets 89,835,000   119,285,000
Recurring | Level 2 | Corporate bonds      
Assets      
Total assets 61,012,000   47,959,000
Recurring | Level 3      
Assets      
Total assets 3,025,000   3,000,000
Total liabilities     93,328,000
Recurring | Level 3 | Private Placement Warrants      
Assets      
Total liabilities     93,328,000
Recurring | Level 3 | Other investments      
Assets      
Total assets $ 3,025,000   $ 3,000,000