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	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Stockholders' Equity (Members' Deficit)
Common Stock	$ 6		$ 4
Additional paid-in capital	936,724		654,685
Accumulated other comprehensive loss	(476)		(129)
Accumulated deficit	(280,033)		(200,857)
Total Cullinan Stockholders' Equity (Members' Deficit)	656,221		453,703
Non-controlling interests in subsidiaries	0		192
Total Stockholders' Equity (Members' Deficit)	$ 656,221	$ 425,665	$ 453,895	$ 499,574	$ 485,649	$ 535,029