v3.25.2
Net Loss per Share Attributable to Cullinan - Summary of Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Numerator:        
Net loss attributable to Cullinan - basic and diluted $ (70,055) $ (42,028) $ (118,556) $ (79,176)
Common Stock        
Numerator:        
Net loss attributable to Cullinan - basic and diluted $ (63,127) $ (37,605) $ (106,825) $ (69,940)
Denominator        
Weighted-average shares outstanding - basic 59,015 55,052 58,960 49,031
Weighted-average shares outstanding - diluted 59,015 55,052 58,960 49,031
Net loss per share attributable to Cullinan:        
Basic $ (1.07) $ (0.68) $ (1.81) $ (1.43)
Diluted $ (1.07) $ (0.68) $ (1.81) $ (1.43)
Preferred Stock        
Numerator:        
Net loss attributable to Cullinan - basic and diluted $ (6,928) $ (4,423) $ (11,731) $ (9,236)
Denominator        
Weighted-average shares outstanding - basic 648 648 648 648
Weighted-average shares outstanding - diluted 648 648 648 648
Net loss per share attributable to Cullinan:        
Basic $ (10.7) $ (6.83) $ (18.12) $ (14.26)
Diluted $ (10.7) $ (6.83) $ (18.12) $ (14.26)