v3.26.1
Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Accounting Policies [Abstract]    
Net income $ 176,787 $ 151,517
Less: Net income attributable to non-controlling interests 2,300 0
Net income attributable to SEI Investments Company $ 174,487 $ 151,517
Shares used to compute basic earnings per common share (in shares) 121,659 126,561
Dilutive effect of stock awards (in shares) 2,835 2,889
Shares used to compute diluted earnings per common share (in shares) 124,494 129,450
Basic earnings per common share (in USD per share) $ 1.43 $ 1.20
Diluted earnings per common share (in USD per share) $ 1.40 $ 1.17