Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Collaboration Revenue—from related party	$ 34,034	$ 2,934
Revenue from Contract with Customer, Product and Service [Extensible List]	kymr:CollaborationRevenueFromRelatedPartyMember	kymr:CollaborationRevenueFromRelatedPartyMember
Operating expenses:
Research and development	$ 62,105	$ 37,158
General and administrative	18,233	7,981
Total operating expenses	80,338	45,139
Loss from operations	(46,304)	(42,205)
Other income (expense):
Interest Income	826	1,005
Interest Expense	(115)	(46)
Total other income	711	959
Net loss	(45,593)	(41,246)
Other comprehensive loss:
Unrealized (loss) gain on marketable securities	(134)	6
Total comprehensive loss	(45,727)	(41,240)
Reconciliation of net loss to net loss attributable to common stockholders:
Net Loss	(45,593)	(41,246)
Deemed dividend from exchange of convertible preferred stock	(9,050)
Net loss attributable to common stockholders	$ (54,643)	$ (41,246)
Net loss per share attributable to common stockholders, basic and diluted	$ (3.15)	$ (24.28)
Weighted average common stocks outstanding, basic and diluted	17,349,582	1,698,522