CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Collaboration Revenue—from related parties	$ 18,519	$ 3,288	$ 37,221	$ 6,716
Revenue from Contract with Customer, Product and Service [Extensible List]	kymr:CollaborationsRevenueMember	kymr:CollaborationsRevenueMember	kymr:CollaborationsRevenueMember	kymr:CollaborationsRevenueMember
Operating expenses:
Research and development	$ 35,220	$ 13,819	$ 61,181	$ 25,935
General and administrative	8,029	3,661	13,939	6,220
Total operating expenses	43,249	17,480	75,120	32,155
Loss from operations	(24,730)	(14,192)	(37,899)	(25,439)
Other income (expense):
Interest Income	98	228	217	577
Interest Expense	(28)	(25)	(53)	(59)
Total other income:	70	203	164	518
Net loss	(24,660)	(13,989)	(37,735)	(24,921)
Other comprehensive loss:
Unrealized gain (loss) on marketable securities	14	(189)	128	25
Total comprehensive loss	(24,646)	(14,178)	(37,607)	(24,896)
Reconciliation of net loss to net loss attributable to common stockholders:
Net Loss	(24,660)	(13,989)	(37,735)	(24,921)
Deemed dividend from exchange of convertible preferred stock				(9,050)
Net loss attributable to common stockholders	$ (24,660)	$ (13,989)	$ (37,735)	$ (33,971)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.55)	$ (6.98)	$ (0.84)	$ (17.18)
Weighted average common stock outstanding, basic and diluted	45,094,238	2,002,825	44,873,083	1,977,720