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	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Stockholders' Equity (Members' Deficit)
Common Stock	$ 4	$ 4
Additional paid-in capital	592,839	584,714
Accumulated other comprehensive loss	(3,134)	(838)
Accumulated deficit	(171,007)	(158,909)
Total Cullinan Stockholders' Equity (Members' Deficit)	418,702	424,971
Non-controlling interests in subsidiaries	768	403
Total Stockholders' Equity (Members' Deficit)	$ 419,470	$ 425,374	$ 469,699	$ 200,314