Business Combination (Details)
$ / shares in Units, $ in Thousands
 1 Months Ended 9 Months Ended 12 Months Ended
Jan. 07, 2021
USD ($)
vote
$ / shares
shares
Jan. 06, 2021
USD ($)
$ / shares
shares
Oct. 05, 2020
USD ($)
shares
Jan. 31, 2021
Sep. 30, 2021
USD ($)
$ / shares
shares
Sep. 30, 2020
USD ($)
Dec. 31, 2020
USD ($)
$ / shares
shares
Dec. 31, 2019
USD ($)
$ / shares
shares
Sep. 09, 2021
$ / shares
Jan. 08, 2021
shares
Apr. 21, 2020
$ / shares
Dec. 31, 2018
shares
Dec. 31, 2017
$ / shares
shares
Nov. 30, 2016
$ / shares
shares
Business Acquisition [Line Items]                            
Common stock, par value, (in dollars per share) | $ / shares             $ 0.0001 $ 0.0001            
Common stock, shares, outstanding (in shares)             89,206,266 88,279,119       87,362,592    
Common stock exchange ratio 206.81%     206.81%     206.81%              
Class of warrant or right, number of securities called by warrants or rights (in shares)                         122,052 139,629
Exercise price of warrants (in dollars per share) | $ / shares                 $ 0.10       $ 3.45 $ 2.61
Proceeds from issuance of common stock | $         $ 5,547 $ 954 $ 1,748 $ 601            
Warrants outstanding (in shares) 38,533,271                 38,533,271        
Preferred stock, shares authorized (in shares)             155,387,025 155,387,025            
Preferred stock par value, (in dollars per share) | $ / shares             $ 0.0001 $ 0.0001            
Preferred stock, shares issued (in shares)             139,444,346 139,444,346            
Preferred stock, shares outstanding (in shares)             139,444,346 139,444,346            
SCH and Merger Sub | Merger Agreement                            
Business Acquisition [Line Items]                            
Business combination, net increase in cash | $ $ 670,000                          
Business combination, transaction costs | $ 61,000                          
Board of Directors                            
Business Acquisition [Line Items]                            
Preferred stock, shares authorized (in shares)         25,000,000                  
Preferred stock par value, (in dollars per share) | $ / shares         $ 0.0001                  
Preferred stock, shares issued (in shares)         0                  
Preferred stock, shares outstanding (in shares)         0                  
PIPE Investment                            
Business Acquisition [Line Items]                            
Business combination, proceeds from private placement | $ 400,000                          
IPO                            
Business Acquisition [Line Items]                            
Business combination, deferred underwriter fees | $ $ 29,000                          
Public Warrants                            
Business Acquisition [Line Items]                            
Warrants outstanding (in shares)         0                  
Private Placement Warrant and Public Warrant                            
Business Acquisition [Line Items]                            
Exercise price of warrants (in dollars per share) | $ / shares $ 11.50                          
Common Class A                            
Business Acquisition [Line Items]                            
Common stock, par value, (in dollars per share) | $ / shares         $ 0.0001   $ 0.0001              
Common stock, shares, outstanding (in shares) 143,475,108       278,308,964   0              
Common Class A | PIPE Investment                            
Business Acquisition [Line Items]                            
Sale of stock, number of shares issued in transaction (in shares)     40,000,000                      
Proceeds from issuance of common stock | $     $ 400,000                      
Common Class A | Private Placement Warrant                            
Business Acquisition [Line Items]                            
Class of warrant or right, number of securities called by warrants or rights (in shares) 10,933,333                          
Common Class A | Public Warrants                            
Business Acquisition [Line Items]                            
Class of warrant or right, number of securities called by warrants or rights (in shares) 27,599,938                          
Common Class A | Clover Health Investments Corp                            
Business Acquisition [Line Items]                            
Common stock, voting rights one vote                          
Common Class A | SCH Sponsor III LLC                            
Business Acquisition [Line Items]                            
Sale of stock, number of shares issued in transaction (in shares)     15,200,000                      
Common Class B                            
Business Acquisition [Line Items]                            
Common stock, par value, (in dollars per share) | $ / shares $ 0.0001       $ 0.0001   $ 0.0001              
Common stock, voting rights per share | vote 10                          
Cash consideration received from business combination | $ $ 499,800                          
Common stock, shares, outstanding (in shares) 260,965,701       142,318,711   89,206,266              
Share price (in dollars per share) | $ / shares $ 10.00                          
Common stock exchange ratio 206.81%     206.81%                    
Pro rata adjustments, percentage 32.30%                          
Common Class A and Class B                            
Business Acquisition [Line Items]                            
Common stock, shares, outstanding (in shares)                   404,440,809        
SCH class B ordinary shares converted to Clover class A common Stock | Social Capital Hedosophia Holdings Corp III                            
Business Acquisition [Line Items]                            
Common stock, par value, (in dollars per share) | $ / shares                     $ 0.0001      
Common stock. conversion basis one-for-one                          
SCH class A ordinary shares converted to Clover class A common Stock | Social Capital Hedosophia Holdings Corp III                            
Business Acquisition [Line Items]                            
Common stock, par value, (in dollars per share) | $ / shares                     $ 0.0001      
Common stock. conversion basis one-for-one                          
Shares redeemed for cash   24,892                        
Sale of stock, price per share (in dollars per share) | $ / shares   $ 10.00                        
Cash paid for redemption of common stock | $   $ 200                        
Redemption price (in dollars per share) | $ / shares   $ 10.00                        
Cash held-in-trust account | $   $ 827,900                        
Balance to pay on merger consideration | $   $ 499,800