CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Statement [Abstract]
Loss from operations	$ (62,756)	$ (32,657)
Type of revenue [Extensible List]	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 52,096	$ 24,536
General and administrative	10,660	8,121
Total operating expenses	62,756	32,657
Other income (expense):
Interest income	4,508	197
Other income (expense), net	107	0
Net income (loss) before income taxes	(58,141)	(32,460)
Income tax benefit	0	(19,568)
Net loss	(58,141)	(12,892)
Net loss attributable to noncontrolling interests	(179)	(794)
Net loss attributable to common stockholders of Cullinan	(57,962)	(12,098)
Comprehensive loss:
Net loss	(58,141)	(12,892)
Unrealized gain (loss) on investments	1,359	(2,296)
Comprehensive loss	(56,782)	(15,188)
Comprehensive loss attributable to noncontrolling interests	(179)	(794)
Comprehensive loss attributable to Cullinan	$ (56,603)	$ (14,394)
Net loss per share:
Basic	$ (1.42)	$ (0.27)
Diluted	$ (1.42)	$ (0.27)
Weighted-average shares used in computing net loss per share:
Basic	40,682	44,432
Diluted	40,682	44,432