v3.26.1
Summary of Significant Accounting Policies - Narrative (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Summary of Significant Accounting Policies [Line Items]        
Amortization expense     $ 19,132 $ 6,606
Anti-dilutive employee stock options (in shares) 4,395 5,713 4,411 5,773
Anti-dilutive employee stock options (in USD per share) $ 75.28 $ 66.08 $ 75.28 $ 66.01
Capitalized Software        
Summary of Significant Accounting Policies [Line Items]        
Capitalized software development costs $ 11,132 $ 14,466 $ 11,132 $ 14,466
Capitalized Software | Investment Managers        
Summary of Significant Accounting Policies [Line Items]        
Capitalized software development costs 3,676 5,615 3,676 5,615
Finite-lived intangible assets, net 40,685   40,685  
Amortization expense     3,016  
Capitalized software in progress $ 3,676   $ 3,676  
Estimated useful life of the SEI Wealth Platform 6 years 1 month 6 days   6 years 1 month 6 days  
Capitalized Software | Investment Managers | SEI Wealth Platform        
Summary of Significant Accounting Policies [Line Items]        
Capitalized software development costs $ 7,456 8,851 $ 7,456 8,851
Finite-lived intangible assets, net 186,530   186,530  
Amortization expense     15,173 14,297
Capitalized software in progress $ 2,232   $ 2,232  
Capitalized Software | Weighted Average | Investment Managers | SEI Wealth Platform        
Summary of Significant Accounting Policies [Line Items]        
Estimated useful life of the SEI Wealth Platform 7 years 3 months 18 days   7 years 3 months 18 days  
SEI-Sponsored Open-Ended Money Market Mutual Funds        
Summary of Significant Accounting Policies [Line Items]        
Fees waived $ 4,776 $ 5,262 $ 9,853 $ 9,395