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, 2023	Dec. 31, 2022	Dec. 31, 2021
Stockholders' Equity (Members' Deficit)
Common Stock	$ 4	$ 5
Additional paid-in capital	654,685	585,320
Accumulated other comprehensive loss	(129)	(2,601)
Accumulated deficit	(200,857)	(47,695)
Total Cullinan Stockholders' Equity (Members' Deficit)	453,703	535,029
Non-controlling interests in subsidiaries	192	0
Total Stockholders' Equity (Members' Deficit)	$ 453,895	$ 535,029	$ 425,374