v3.23.1
Stock-based compensation expense - Additional information (Details)
$ / shares in Units, $ in Millions
12 Months Ended
Sep. 26, 2018
shares
Sep. 30, 2022
USD ($)
$ / shares
shares
Sep. 30, 2021
USD ($)
$ / shares
shares
Sep. 30, 2020
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Aggregate number of common stock shares reserved for issuance (in shares) | shares   507,000 355,000  
Total grant date fair value of stock options   $ 15.8    
Granted (in dollars per share) | $ / shares   $ 24.03 $ 42.80 $ 20.76
Capitalized computer software, net   $ 5.3 $ 3.0  
Share-based liabilities settled   $ 4.6    
Employer matching percentage   50.00%    
Percentage of employee's gross pay matched   6.00%    
Employer matching contributions   $ 2.0    
2018 Equity Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Maximum aggregate number of shares (in shares) | shares 6,856,405      
Minimum annual increase in share reserved for issuance | shares 999,900      
Annual automatic Increase in share reserved for issuance (as a percent) 4.00%      
Aggregate number of common stock shares reserved for issuance (in shares) | shares   1,142,937    
2018 ESPP        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Minimum annual increase in share reserved for issuance | shares 249,470      
Annual automatic Increase in share reserved for issuance (as a percent) 1.00%      
Aggregate number of common stock shares reserved for issuance (in shares) | shares 275,225      
Percentage of payroll deduction to purchase common stock 15.00%      
ESPP eligible employee common stock purchase price ratio 85.00%      
Restricted Stock Units and Performance Stock Units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Granted (in dollars per share) | $ / shares     $ 113.06  
Restricted Stock Unit        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   4 years    
Conversion ratio   1    
Unrecognized compensation cost   $ 92.2    
Recognize cost weighted average period   2 years 8 months 12 days    
Grant date fair value   $ 96.2    
Granted (in dollars per share) | $ / shares   $ 67.30   $ 38.66
Restricted Stock Unit | Director        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   1 year    
Performance Stock Unit        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unrecognized compensation cost   $ 21.6    
Recognize cost weighted average period   1 year 6 months    
Grant date fair value   $ 49.0    
Granted (in dollars per share) | $ / shares   $ 78.81    
Performance Stock Unit | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of PSUs that may vest based on performance   0.00%    
Performance Stock Unit | Minimum | Employee        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   1 year    
Performance Stock Unit | Minimum | Non-Employee        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   1 year    
Performance Stock Unit | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of PSUs that may vest based on performance   150.00%    
Performance Stock Unit | Maximum | Employee        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   3 years    
Performance Stock Unit | Maximum | Non-Employee        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   3 years    
Option        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   4 years    
Unrecognized compensation cost   $ 12.2    
Recognize cost weighted average period   1 year 1 month 6 days    
Award term   10 years    
Dividend yield   0.00%    
Tax benefit   $ 44.2    
Performance Stock Options        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unrecognized compensation cost   $ 0.9    
Recognize cost weighted average period   1 year 10 months 24 days    
Award term   10 years    
Dividend yield   0.00% 0.00% 0.00%
Total grant date fair value of stock options   $ 1.5    
Granted (in dollars per share) | $ / shares   $ 31.29 $ 45.18 $ 43.06
Performance Stock Options | Non-Employee        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   5 years    
Performance Stock Options | Executive Officers and Senior Level Employees        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   2 years    
Vest outstanding (in shares) | shares   293,730    
Performance Stock Options | Minimum | Executive Officers and Senior Level Employees        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of PSUs that may vest based on performance   0.00%    
Performance Stock Options | Maximum | Executive Officers and Senior Level Employees        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of PSUs that may vest based on performance   150.00%    
Share-based Payment Arrangement        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Capitalized computer software, net   $ 0.7