v3.26.1
Fair Value Measurements (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Available-for-sale securities $ 141,249 $ 158,690
Securities owned 25,532 33,777
Total financial assets measured at fair value 380,203 385,751
Total financial liabilities measured at fair value 127,772 116,077
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 25,532 33,777
Total financial assets measured at fair value 250,131  
Contingent considerations 6,736 7,834
Total financial liabilities measured at fair value 6,736 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 130,072 113,119
Securities sold short 121,036 108,243
Total financial liabilities measured at fair value 121,036 108,243
Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total financial assets measured at fair value 199,723 180,533
Total financial liabilities measured at fair value 121,036 108,243
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 69,651  
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 130,072 113,119
Securities sold short 121,036 108,243
Total financial liabilities measured at fair value 121,036 108,243
Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total financial assets measured at fair value 166,781 192,467
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 25,532 33,777
Total financial assets measured at fair value 166,781  
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 6,736 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 6,736 7,834
Total financial liabilities measured at fair value 6,736 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 13,699 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 13,699  
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 69,651  
Equity securities | Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 130,072  
Equity securities | Level 1 | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 69,651  
Equity securities | Level 1 | Consolidated VIEs    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 130,072  
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 138,598 158,690
Available-for-sale debt securities | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Available-for-sale securities 141,249  
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 141,249  
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 12,922 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 12,922 11,593
Investments in limited partnership funds | SEI Investments Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments measured at NAV 777 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 $ 777 $ 1,158