CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Collaboration Revenue—from related parties	$ 18,702	$ 3,428
Revenue from Contract with Customer, Product and Service [Extensible List]	kymr:CollaborationRevenueMember	kymr:CollaborationRevenueMember
Operating expenses:
Research and development	$ 25,962	$ 12,116
General and administrative	5,909	2,559
Total operating expenses	31,871	14,675
Loss from operations	(13,169)	(11,247)
Other income (expense):
Interest Income	118	349
Interest Expense	(24)	(34)
Total other income:	94	315
Net loss	(13,075)	(10,932)
Other comprehensive loss:
Unrealized gain on marketable securities	115	214
Total comprehensive loss	(12,960)	(10,718)
Reconciliation of net loss to net loss attributable to common stockholders:
Net Loss	(13,075)	(10,932)
Deemed dividend from exchange of convertible preferred stock		(9,050)
Net loss attributable to common stockholders	$ (13,075)	$ (19,982)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.29)	$ (10.23)
Weighted average common stock outstanding, basic and diluted	44,649,572	1,952,667