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, 2021	Dec. 31, 2020		Dec. 31, 2019
Redeemable Preferred Units
Total Redeemable Preferred Units
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units
Common Stock	$ 4	3	[1]	2
Additional paid-in capital	584,714	292,348	[1]	138,543
Accumulated other comprehensive loss	(838)	(2)	[1]	(4)
Accumulated deficit	(158,909)	(93,339)	[1]	(41,540)
Total Cullinan Stockholders' Equity (Members' Deficit)	424,971	199,010	[1]	97,001
Non-controlling interests in subsidiaries	403	1,304	[1]	864
Total Stockholders' Equity (Members' Deficit)	$ 425,374	200,314	[1]	97,865	[2]
As Reported
Redeemable Preferred Units
Total Redeemable Preferred Units		276,652		137,774
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units		1		1
Common Stock
Additional paid-in capital		15,698		770
Accumulated other comprehensive loss		(2)		(4)
Accumulated deficit		(93,339)		(41,540)
Total Cullinan Stockholders' Equity (Members' Deficit)		(77,642)		(40,773)
Non-controlling interests in subsidiaries		1,304		864
Total Stockholders' Equity (Members' Deficit)		(76,338)		(39,909)
Adjustment
Redeemable Preferred Units
Total Redeemable Preferred Units		(276,652)		(137,774)
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units		(1)		(1)
Common Stock		3		2
Additional paid-in capital		276,650		137,773
Accumulated other comprehensive loss
Accumulated deficit
Total Cullinan Stockholders' Equity (Members' Deficit)		276,652		137,774
Non-controlling interests in subsidiaries
Total Stockholders' Equity (Members' Deficit)		276,652		137,774
Series Seed Redeemable Preferred Units
Redeemable Preferred Units
Total Redeemable Preferred Units
Series Seed Redeemable Preferred Units | As Reported
Redeemable Preferred Units
Total Redeemable Preferred Units		3,956		3,956
Series Seed Redeemable Preferred Units | Adjustment
Redeemable Preferred Units
Total Redeemable Preferred Units		(3,956)		(3,956)
Series A1 Redeemable Preferred Units
Redeemable Preferred Units
Total Redeemable Preferred Units
Series A1 Redeemable Preferred Units | As Reported
Redeemable Preferred Units
Total Redeemable Preferred Units		49,946		49,946
Series A1 Redeemable Preferred Units | Adjustment
Redeemable Preferred Units
Total Redeemable Preferred Units		(49,946)		(49,946)
Series B Redeemable Preferred Units
Redeemable Preferred Units
Total Redeemable Preferred Units
Series B Redeemable Preferred Units | As Reported
Redeemable Preferred Units
Total Redeemable Preferred Units		97,909		83,872
Series B Redeemable Preferred Units | Adjustment
Redeemable Preferred Units
Total Redeemable Preferred Units		(97,909)		(83,872)
Series C Redeemable Preferred Units
Redeemable Preferred Units
Total Redeemable Preferred Units
Series C Redeemable Preferred Units | As Reported
Redeemable Preferred Units
Total Redeemable Preferred Units		124,841
Series C Redeemable Preferred Units | Adjustment
Redeemable Preferred Units
Total Redeemable Preferred Units		$ (124,841)

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

[2] The consolidated balance sheets as of December 31, 2020 and 2019 are derived from the consolidated financial statements as of such date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the consolidated financial statements for additional details.