CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Operating expenses:
Research and development	$ 41,459	$ 30,646
General and administrative	13,537	12,343
Total operating expenses	54,996	42,989
Loss from operations	(54,996)	(42,989)
Other income (expense):
Interest income	6,580	5,693
Other expense, net	(85)	(44)
Net loss	(48,501)	(37,340)
Net loss attributable to noncontrolling interests	0	(192)
Net loss attributable to Cullinan	(48,501)	(37,148)
Comprehensive income (loss):
Net loss	(48,501)	(37,340)
Unrealized gain (loss) on investments	638	(202)
Comprehensive loss	(47,863)	(37,542)
Comprehensive loss attributable to noncontrolling interests	0	(192)
Comprehensive loss attributable to Cullinan	(47,863)	(37,350)
Common Stock
Other income (expense):
Net loss attributable to Cullinan	$ (43,698)	$ (32,287)
Basic and diluted net loss per share attributable to Cullinan:
Net loss per share, basic	$ (0.74)	$ (0.75)
Net loss per share, diluted	$ (0.74)	$ (0.75)
Weighted-average shares used in computing basic and diluted net loss per share attributable to Cullinan:
Weighted-average common stock outstanding - basic	58,905	43,011
Weighted-average common stock outstanding - diluted	58,905	43,011
Preferred Stock
Other income (expense):
Net loss attributable to Cullinan	$ (4,803)	$ (4,861)
Basic and diluted net loss per share attributable to Cullinan:
Net loss per share, basic	$ (7.42)	$ (7.51)
Net loss per share, diluted	$ (7.42)	$ (7.51)
Weighted-average shares used in computing basic and diluted net loss per share attributable to Cullinan:
Weighted-average common stock outstanding - basic	648	648
Weighted-average common stock outstanding - diluted	648	648