v3.26.1
Summary of Significant Accounting Policies - Earnings Per Share (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
Accounting Policies [Abstract]        
Net income $ 199,540 $ 227,083 $ 376,327 $ 378,600
Less: Net income attributable to non-controlling interests 3,882 0 6,182 0
Net income attributable to SEI Investments Company $ 195,658 $ 227,083 $ 370,145 $ 378,600
Shares used to compute basic earnings per common share (in shares) 120,339 124,470 120,999 125,516
Dilutive effect of stock awards (in shares) 2,995 2,808 2,915 2,848
Shares used to compute diluted earnings per common share (in shares) 123,334 127,278 123,914 128,364
Basic earnings per common share (in USD per share) $ 1.63 $ 1.82 $ 3.06 $ 3.02
Diluted earnings per common share (in USD per share) $ 1.59 $ 1.78 $ 2.99 $ 2.95