CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Collaboration Revenue—from related parties	$ 14,533	$ 950	$ 21,249	$ 1,101
Revenue from Contract with Customer, Product and Service [Extensible List]	kymr:CollaborationRevenueMember	kymr:CollaborationRevenueMember	kymr:CollaborationRevenueMember	kymr:CollaborationRevenueMember
Operating expenses:
Research and development	$ 15,778	$ 11,310	$ 41,713	$ 26,072
General and administrative	6,838	1,501	13,058	5,451
Total operating expenses	22,616	12,811	54,771	31,523
Loss from operations	(8,083)	(11,861)	(33,522)	(30,422)
Other income (expense):
Interest Income	125	445	702	705
Interest Expense	(28)	(4)	(88)	(16)
Total other income:	97	441	614	689
Net loss	(7,986)	(11,420)	(32,908)	(29,733)
Other comprehensive loss:
Unrealized loss on marketable securities	(195)		(170)
Total comprehensive loss	(8,181)	(11,420)	(33,078)	(29,733)
Reconciliation of net loss to net loss attributable to common stockholders:
Net loss	(7,986)	(11,420)	(32,908)	(29,733)
Deemed dividend from exchange of convertible preferred stock			(9,050)
Net loss attributable to common stockholders	$ (7,986)	$ (11,420)	$ (41,958)	$ (29,733)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.39)	$ (6.54)	$ (5.11)	$ (18.15)
Weighted average common stocks outstanding, basic and diluted	20,677,392	1,745,404	8,211,003	1,638,579