v3.26.3
Stock-based Compensation - Equity Incentive Plans, Additional Information (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Jun. 06, 2024
Oct. 22, 2019
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Dec. 31, 2024
Stock-based compensation                
Number of shares outstanding (in shares)     10,420,735 14,460,365 10,420,735 14,460,365 13,992,173 16,511,128
Stock-based compensation expense     $ 24,442 $ 11,597 $ 49,691 $ 29,871    
ESPP                
Stock-based compensation                
Stock-based compensation expense     $ 100 $ 100 $ 300 $ 400    
2019 Waystar Holding Plan                
Stock-based compensation                
Maximum shares issuable (in shares)   9,900,000            
Contractual term   10 years            
Number of shares outstanding (in shares)   1,800,000            
2019 Waystar Holding Plan | Stock Options                
Stock-based compensation                
Vesting period of awards   5 years            
Vesting percentage of options with a service condition (in percent)   20.00%            
2024 Equity Incentive Plan                
Stock-based compensation                
Maximum shares issuable (in shares) 10,000,000              
Percentage of outstanding common stock 5.00%              
Common stock, capital shares reserved for future issuance     3,000,000.0   3,000,000.0      
2024 Equity Incentive Plan | Stock Options                
Stock-based compensation                
Vesting period of awards 5 years              
Vesting percentage of options with a service condition (in percent) 20.00%              
2024 Equity Incentive Plan | RSUs | Minimum                
Stock-based compensation                
Vesting period of awards 2 years              
2024 Equity Incentive Plan | RSUs | Maximum                
Stock-based compensation                
Vesting period of awards 5 years              
2024 Equity Incentive Plan | Performance Stock Units With Market-Based Conditions                
Stock-based compensation                
Performance period 4 years              
2024 Equity Incentive Plan | Performance Stock Units With Market-Based Conditions | Minimum                
Stock-based compensation                
Vesting percentage of options with a service condition (in percent) 0.00%              
2024 Equity Incentive Plan | Performance Stock Units With Market-Based Conditions | Maximum                
Stock-based compensation                
Vesting percentage of options with a service condition (in percent) 200.00%              
2024 Equity Incentive Plan | Performance Stock Units With Performance-Based Conditions                
Stock-based compensation                
Vesting period of awards         3 years      
Performance period 3 years       3 years      
2024 Equity Incentive Plan | Performance Stock Units With Performance-Based Conditions | Minimum                
Stock-based compensation                
Vesting percentage of options with a service condition (in percent) 0.00%       0.00%      
2024 Equity Incentive Plan | Performance Stock Units With Performance-Based Conditions | Maximum                
Stock-based compensation                
Vesting percentage of options with a service condition (in percent) 200.00%       200.00%      
2024 Employee Stock Purchase Plan                
Stock-based compensation                
Percentage of outstanding common stock 1.00%              
Common stock, capital shares reserved for future issuance 3,250,000              
Common stock issued under employee stock purchase plan (in shares)     69,000 37,323 120,221 37,323    
2024 Employee Stock Purchase Plan | Maximum                
Stock-based compensation                
Shares available for future grant (in shares) 27,000,000              
2024 Employee Stock Purchase Plan | ESPP                
Stock-based compensation                
ESPP discount rate (as a percent) 15.00%