CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 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	$ 24,536	$ 12,415
General and administrative	8,121	5,156
Total operating expenses	32,657	17,571
Income/(loss) from operations	(32,657)	1,372
Other income (expense):
Interest income	197	49
Other income (expense), net	0	(2)
Net income/(loss) before income taxes	(32,460)	1,419
Income tax expense/(benefit)	19,568	0
Net income/(loss)	(12,892)	1,419
Net income/(loss) attributable to noncontrolling interest	(794)	1,489
Net loss attributable to common stockholders of Cullinan	$ (12,098)	$ (70)
Net loss per share, basic and diluted	$ (0.27)	$ (0.00)
Total weighted-average shares used in computing net loss per share, basic and diluted	44,431,657	41,977,336
Comprehensive income/(loss):
Net income/(loss)	$ (12,892)	$ 1,419
Unrealized gain/(loss) on investments	(2,296)	(58)
Comprehensive income/(loss)	(15,188)	1,361
Comprehensive income/(loss) attributable to noncontrolling interest	(794)	1,489
Comprehensive income/(loss) attributable to Cullinan	$ (14,394)	$ (128)