Annual report pursuant to Section 13 and 15(d)

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

v3.21.1
FAIR VALUE MEASUREMENTS - Assets measured on recurring basis (Details) - USD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Liabilities:    
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
Level 3    
Liabilities:    
Additions 3,000,000  
Balance at end of year 3,000,000  
Recurring    
Assets:    
Total assets at fair value 597,753,000 150,209,000
Liabilities:    
Total liabilities at fair value 93,328,000  
Recurring | Private Placement Warrants    
Liabilities:    
Total liabilities at fair value 93,328,000  
Recurring | Money market funds    
Assets:    
Total assets at fair value 407,512,000 40,454,000
Recurring | Commercial paper    
Assets:    
Total assets at fair value 119,285,000 19,938,000
Recurring | Corporate bonds    
Assets:    
Total assets at fair value 47,959,000 48,010,000
Recurring | U.S Treasury securities    
Assets:    
Total assets at fair value 19,997,000  
Recurring | Other investments    
Assets:    
Total assets at fair value 3,000,000  
Recurring | Assetbacked securities    
Assets:    
Total assets at fair value   16,806,000
Recurring | Repurchase agreements    
Assets:    
Total assets at fair value   25,001,000
Recurring | Level 1    
Assets:    
Total assets at fair value 427,509,000 40,454,000
Recurring | Level 1 | Money market funds    
Assets:    
Total assets at fair value 407,512,000 40,454,000
Recurring | Level 1 | U.S Treasury securities    
Assets:    
Total assets at fair value 19,997,000  
Recurring | Level 2    
Assets:    
Total assets at fair value 167,244,000 109,755,000
Recurring | Level 2 | Commercial paper    
Assets:    
Total assets at fair value 119,285,000 19,938,000
Recurring | Level 2 | Corporate bonds    
Assets:    
Total assets at fair value 47,959,000 48,010,000
Recurring | Level 2 | Assetbacked securities    
Assets:    
Total assets at fair value   16,806,000
Recurring | Level 2 | Repurchase agreements    
Assets:    
Total assets at fair value   $ 25,001,000
Recurring | Level 3    
Assets:    
Total assets at fair value 3,000,000  
Liabilities:    
Total liabilities at fair value 93,328,000  
Recurring | Level 3 | Private Placement Warrants    
Liabilities:    
Total liabilities at fair value 93,328,000  
Recurring | Level 3 | Other investments    
Assets:    
Total assets at fair value $ 3,000,000