General form of registration statement for all companies including face-amount certificate companies

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

v3.21.2
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
Liabilities:        
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
Level 3        
Liabilities:        
Balance at beginning of year 3,000,000      
Additions     3,000,000  
Balance at end of year 3,025,000   3,000,000  
Recurring        
Assets:        
Total assets at fair value 571,961,000   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 413,089,000   407,512,000 40,454,000
Recurring | Commercial paper        
Assets:        
Total assets at fair value 89,835,000   119,285,000 19,938,000
Recurring | Corporate bonds        
Assets:        
Total assets at fair value 61,012,000   47,959,000 48,010,000
Recurring | U.S Treasury securities        
Assets:        
Total assets at fair value 5,000,000   19,997,000  
Recurring | Other investments        
Assets:        
Total assets at fair value 3,025,000   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 418,089,000   427,509,000 40,454,000
Recurring | Level 1 | Money market funds        
Assets:        
Total assets at fair value 413,089,000   407,512,000 40,454,000
Recurring | Level 1 | U.S Treasury securities        
Assets:        
Total assets at fair value 5,000,000   19,997,000  
Recurring | Level 2        
Assets:        
Total assets at fair value 150,847,000   167,244,000 109,755,000
Recurring | Level 2 | Commercial paper        
Assets:        
Total assets at fair value 89,835,000   119,285,000 19,938,000
Recurring | Level 2 | Corporate bonds        
Assets:        
Total assets at fair value 61,012,000   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 3,025,000   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 $ 3,025,000   $ 3,000,000