Post-effective amendment to a registration statement that is not immediately effective upon filing

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 12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Assets        
Level 1 to Level 2 transfer $ 0 $ 0 $ 0 $ 0
Level 2 to Level 1 transfer 0 0 0 0
Transfer into Level 3 0 0 0 0
Transfer out of Level 3 0 0 0 0
Movement in Level 3 liabilities measured at fair value        
Balance at beginning of period 93,328,000 $ 0 0  
Changes in fair value 56,576,000      
Exercise of private placement warrants (149,904,000)      
Balance at end of period     93,328,000 0
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   3,000,000  
Additions     3,000,000  
Recurring        
Assets        
Total assets 571,961,000   597,753,000 150,209,000
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 40,454,000
Recurring | Commercial paper        
Assets        
Total assets 89,835,000   119,285,000 19,938,000
Recurring | Corporate bonds        
Assets        
Total assets 61,012,000   47,959,000 48,010,000
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 | Assetbacked securities        
Assets        
Total assets       16,806,000
Recurring | Repurchase agreements        
Assets        
Total assets       25,001,000
Recurring | Level 1        
Assets        
Total assets 418,089,000   427,509,000 40,454,000
Recurring | Level 1 | Money market funds        
Assets        
Total assets 413,089,000   407,512,000 40,454,000
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   167,244,000 109,755,000
Recurring | Level 2 | Commercial paper        
Assets        
Total assets 89,835,000   119,285,000 19,938,000
Recurring | Level 2 | Corporate bonds        
Assets        
Total assets 61,012,000   47,959,000 48,010,000
Recurring | Level 2 | Assetbacked securities        
Assets        
Total assets       16,806,000
Recurring | Level 2 | Repurchase agreements        
Assets        
Total assets       $ 25,001,000
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