Net Loss per Share - Summary of Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	[1],[2]
Numerator:
Net loss attributable to common stockholders of Cullinan	$ (65,570)	$ (51,799)
Denominator
Total weighted-average shares used in computing net loss per share, basic and diluted	43,077,330	19,887,307
Net Loss per share:	$ (1.52)	$ (2.60)

[1] The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.

[2] The shares and per share amounts for the year ended December 31, 2020 were derived from the consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the for additional details.