CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Operating expenses:
Research and development	$ 142,903	$ 148,156
General and administrative	54,016	42,493
Total operating expenses	196,919	190,649
Impairment of long-lived assets	0	(440)
Loss from operations	(196,919)	(191,089)
Other income (expense):
Interest income	29,660	21,627
Other income (expense), net	(199)	239
Net loss before income taxes	(167,458)	(169,223)
Income tax expense (benefit)	117	(14,122)
Net loss	(167,575)	(155,101)
Net loss attributable to noncontrolling interests	(192)	(1,939)
Net loss attributable to Cullinan	(167,383)	(153,162)
Comprehensive income (loss):
Net loss	(167,575)	(155,101)
Unrealized gain (loss) on investments	(4)	2,472
Comprehensive loss	(167,579)	(152,629)
Comprehensive loss attributable to noncontrolling interests	(192)	(1,939)
Comprehensive loss attributable to Cullinan	(167,387)	(150,690)
Common Stock
Other income (expense):
Net loss attributable to Cullinan	$ (149,393)	$ (133,448)
Basic and diluted net loss per share attributable to Cullinan:
Basic	$ (2.78)	$ (3.21)
Diluted	$ (2.78)	$ (3.21)
Weighted-average shares used in computing basic and diluted net loss per share attributable to Cullinan:
Basic	53,771	41,550
Diluted	53,771	41,550
Preferred Stock
Other income (expense):
Net loss attributable to Cullinan	$ (17,990)	$ (19,714)
Basic and diluted net loss per share attributable to Cullinan:
Basic	$ (27.78)	$ (32.12)
Diluted	$ (27.78)	$ (32.12)
Weighted-average shares used in computing basic and diluted net loss per share attributable to Cullinan:
Basic	648	614
Diluted	648	614