Reorganization and Reverse Stock Split - Summary of LLC Units Previously Reported as Redeemable Preferred Units or Temporary Equity Converted Reclassified to Equity (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Stockholders' Equity (Members' Deficit)
Common Stock	$ 6	$ 4
Additional paid-in capital	958,695	654,685
Accumulated other comprehensive loss	(133)	(129)
Accumulated deficit	(368,240)	(200,857)
Total Cullinan Stockholders' Equity (Members' Deficit)	590,328	453,703
Non-controlling interests in subsidiaries	0	192
Total Stockholders' Equity (Members' Deficit)	$ 590,328	$ 453,895	$ 535,029