CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Statement [Abstract]
Revenue	$ 0	$ 18,943
Type of revenue [Extensible List]	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 91,948	$ 57,751
General and administrative	40,189	29,146
Total operating expenses	132,137	86,897
Gain on sale of Cullinan Pearl	276,785	0
Income (loss) from operations	144,648	(67,954)
Other income (expense):
Interest income	6,611	477
Other income (expense), net	57	(8)
Net income (loss) before income taxes	151,316	(67,485)
Income tax expense	42,121	0
Net income (loss)	109,195	(67,485)
Net loss attributable to noncontrolling interest	(2,019)	(1,915)
Net income (loss) attributable to common stockholders of Cullinan	111,214	(65,570)
Comprehensive income (loss):
Net income (loss)	109,195	(67,485)
Unrealized loss on investments	(1,763)	(836)
Comprehensive income (loss)	107,432	(68,321)
Comprehensive loss attributable to noncontrolling interest	(2,019)	(1,915)
Comprehensive income (loss) attributable to Cullinan	$ 109,451	$ (66,406)
Earnings (net loss) per share:
Earnings Per Share, Basic	$ 2.46	$ (1.52)
Earnings Per Share, Diluted	$ 2.38	$ (1.52)
Weighted-average shares used in computing earnings (net loss) per share:
Weighted Average Number of Shares Outstanding, Basic	45,164	43,077
Weighted Average Number of Shares Outstanding, Diluted	46,640	43,077