Share-Based Employee Compensation - Additional Information (Details)
3 Months Ended 12 Months Ended
Jul. 17, 2019
shares
Mar. 31, 2019
shares
Dec. 31, 2021
USD ($)
Tranche
Installment
$ / shares
shares
Dec. 31, 2020
USD ($)
$ / shares
Dec. 31, 2019
USD ($)
shares
Dec. 31, 2018
USD ($)
shares
Dec. 31, 2017
shares
Restricted Stock              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Vesting percentage     50.00%        
Vesting description     50% of the RSAs scheduled to vest in three (3) equal installments on the third, fourth and fifth anniversaries of November 18, 2016, subject to the recipient’s continued employment through the vesting date, and 50% subject to the recipient’s continued employment through February 1, 2021 and the satisfaction of a performance-based vesting condition.        
Share-based compensation expense     $ 41,715,000 $ 48,045,000 $ 23,198,000    
Exchange of shares with stockholders on liquidation | shares 6,309,049   6,309,049        
Number of equal vesting installments | Installment     3        
Vesting upon satisfaction of condition     50.00%        
Stock Option              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Unrecognized compensation cost     $ 829,000        
Expected to be recognized period     6 months        
Restricted Stock Units              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Share-based compensation expense     $ 6,104,000 2,148,000 $ 530,000    
Unrecognized compensation cost     $ 21,915,000        
Expected to be recognized period     3 years 1 month 6 days        
Fair value of RSUs vested     $ 2,760,000        
Stock Appreciation Rights (SARs)              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Share-based compensation expense     3,432,000 $ 1,298,000      
Unrecognized compensation cost     $ 12,219,000        
Number of shares, granted | shares     894,411   831,902    
Exercise price | $ / shares     $ 25.59 $ 28.42      
Expected to be recognized period     3 years        
2019 Equity Incentive Plan              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Share available for issuance under the plan | shares     2,006,495        
2019 Equity Incentive Plan | Stock Option              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Vesting description     Each of these options is scheduled to vest and become exercisable in substantially equal installments on each of the first three anniversaries of July 18, 2019, subject to the recipient’s continued employment through the vesting date and have a ten-year contractual term.        
Number of shares, granted | shares     918,981        
Exercise price | $ / shares     $ 22        
Contractual term     10 years        
2019 Equity Incentive Plan | Stock Appreciation Rights (SARs)              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Vesting description     Each SAR has a strike price equal to the fair market value of the Company’s common stock on the date of grant and is scheduled to vest and become exercisable in substantially equal installments on each of the first four anniversaries of their grant date, subject to the recipient’s continued employment through the vesting date, and have a ten-year contractual term.        
Contractual term     10 years        
Class C Common Units              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Number of shares authorized | shares           151,188  
Possible expiration period     8 years        
Vested units | shares             0
Unrecognized compensation cost         $ 0 $ 29,051,000  
Number of shares, granted | shares   120.02          
Class C Common Units | AssetMark Holdings LLC              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Number of tranches | Tranche     2        
Vesting description     5-year requisite service period for 50% of the units and over an 8-year requisite service period for the remaining 50% of the units.        
Share-based compensation expense         $ 11,407,000 $ 6,568,000  
Class C Common Units | Time Vesting Units | AssetMark Holdings LLC              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Vesting units requisite service period     5 years        
Vesting percentage     50.00%        
Class C Common Units | Performance Vesting Units | AssetMark Holdings LLC              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Vesting units requisite service period     8 years        
Vesting percentage     50.00%