Fair Value Measurements - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value Disclosures [Abstract]
Fair value of warrant liability (less than)	$ 0.1	$ 0.1

Warrants And Rights Outstanding, Fair Value Disclosure

No definition available.

Name:	lmnd_WarrantsAndRightsOutstandingFairValueDisclosure
Namespace Prefix:	lmnd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant