v3.26.1
Fair Value Measurements (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Available-for-sale securities $ 161,221 $ 158,690
Securities owned 32,093 33,777
Total financial assets measured at fair value 396,930 385,751
Total financial liabilities measured at fair value 127,968 116,077
SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities   67,414
Available-for-sale securities   158,690
Securities owned 32,093 33,777
Total financial assets measured at fair value 274,363  
Contingent considerations 7,834 7,834
Total financial liabilities measured at fair value 7,834 7,834
Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities   113,119
Total financial assets measured at fair value 122,567 113,119
Securities sold short 120,134 108,243
Total financial liabilities measured at fair value 120,134 108,243
Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total financial assets measured at fair value 189,946 180,533
Total financial liabilities measured at fair value 120,134 108,243
Level 1 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities   67,414
Available-for-sale securities   0
Securities owned 0 0
Total financial assets measured at fair value 67,379  
Contingent considerations 0 0
Total financial liabilities measured at fair value 0 0
Level 1 | Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities   113,119
Total financial assets measured at fair value 122,567 113,119
Securities sold short 120,134 108,243
Total financial liabilities measured at fair value 120,134 108,243
Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total financial assets measured at fair value 193,314 192,467
Total financial liabilities measured at fair value 0 0
Level 2 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities   0
Available-for-sale securities   158,690
Securities owned 32,093 33,777
Total financial assets measured at fair value 193,314  
Contingent considerations 0 0
Total financial liabilities measured at fair value 0 0
Level 2 | Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities   0
Total financial assets measured at fair value 0 0
Securities sold short 0 0
Total financial liabilities measured at fair value 0 0
Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total financial assets measured at fair value 0 0
Total financial liabilities measured at fair value 7,834 7,834
Level 3 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities   0
Available-for-sale securities   0
Securities owned 0 0
Total financial assets measured at fair value 0  
Contingent considerations 7,834 7,834
Total financial liabilities measured at fair value 7,834 7,834
Level 3 | Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities   0
Total financial assets measured at fair value 0 0
Securities sold short 0 0
Total financial liabilities measured at fair value 0 0
NAV as a Practical Expedient    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total financial assets measured at fair value 13,670 12,751
Total financial liabilities measured at fair value 0 0
NAV as a Practical Expedient | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities   0
Available-for-sale securities   0
Securities owned 0 0
Total financial assets measured at fair value 13,670  
Contingent considerations 0 0
Total financial liabilities measured at fair value 0 0
NAV as a Practical Expedient | Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities   0
Total financial assets measured at fair value 0 0
Securities sold short 0 0
Total financial liabilities measured at fair value 0 0
Equity securities | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 67,379  
Equity securities | Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 122,567  
Equity securities | Level 1 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 67,379  
Equity securities | Level 1 | Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 122,567  
Equity securities | Level 2 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 0  
Equity securities | Level 2 | Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 0  
Equity securities | Level 3 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 0  
Equity securities | Level 3 | Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 0  
Equity securities | NAV as a Practical Expedient | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 0  
Equity securities | NAV as a Practical Expedient | Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 0  
Available-for-sale debt securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Available-for-sale securities 148,628 158,690
Available-for-sale debt securities | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Available-for-sale securities 161,221  
Available-for-sale debt securities | Level 1 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Available-for-sale securities 0  
Available-for-sale debt securities | Level 2 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Available-for-sale securities 161,221  
Available-for-sale debt securities | Level 3 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Available-for-sale securities 0  
Available-for-sale debt securities | NAV as a Practical Expedient | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Available-for-sale securities 0  
Investment funds sponsored by LSV | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments measured at NAV 12,389 11,593
Investment funds sponsored by LSV | Level 1 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments measured at NAV 0 0
Investment funds sponsored by LSV | Level 2 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments measured at NAV 0 0
Investment funds sponsored by LSV | Level 3 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments measured at NAV 0 0
Investment funds sponsored by LSV | NAV as a Practical Expedient | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments measured at NAV 12,389 11,593
Investments in limited partnership funds | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments measured at NAV 1,281 1,158
Investments in limited partnership funds | Level 1 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments measured at NAV 0 0
Investments in limited partnership funds | Level 2 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments measured at NAV 0 0
Investments in limited partnership funds | Level 3 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments measured at NAV 0 0
Investments in limited partnership funds | NAV as a Practical Expedient | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments measured at NAV $ 1,281 $ 1,158