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, 2022	Dec. 31, 2021	Dec. 31, 2020
Stockholders' Equity (Members' Deficit)
Common Stock	$ 5	$ 4
Additional paid-in capital	585,320	584,714
Accumulated other comprehensive loss	(2,601)	(838)
Accumulated deficit	(47,695)	(158,909)
Total Cullinan Stockholders' Equity (Members' Deficit)	535,029	424,971
Non-controlling interests in subsidiaries	0	403
Total Stockholders' Equity (Members' Deficit)	$ 535,029	$ 425,374	$ 200,315