v3.26.3
Earnings Per Share - Computation of basic and diluted net income per share (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Earnings Per Share [Abstract]          
Net income attributable to APAM $ 75,196 $ 66,830 $ 214,065 $ 195,524  
Less: Allocation to participating securities 6,069 5,582 17,840 16,384  
Net income available to common stockholders $ 69,127 $ 61,248 $ 196,225 $ 179,140  
Basic weighted average shares outstanding (in shares) 66,380,225 65,666,782 66,288,288 65,562,800  
Dilutive effect of nonparticipating share-based awards (in shares) 0 0 0 0  
Diluted weighted average shares outstanding (in shares) 66,380,225 65,666,782 66,288,288 65,562,800  
Earnings per share - Basic (in dollars per share) $ 1.04 $ 0.93 $ 2.96 $ 2.73  
Earnings per share - Diluted (in dollars per share) $ 1.04 $ 0.93 $ 2.96 $ 2.73  
Performance Shares          
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]          
Unvested - Number of awards (in shares) 152,207   152,207   152,207