Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Oct. 14, 2022	Dec. 31, 2021	Dec. 31, 2020	Sep. 30, 2023	Dec. 31, 2022	Jul. 07, 2020
Sale of Stock [Line Items]
Common stock, authorized (in shares)				200,000,000	200,000,000	200,000,000
Common stock, par value (usd per share)				$ 0.00001	$ 0.00001	$ 0.00001
Preferred stock, authorized (in shares)				10,000,000	10,000,000	10,000,000
Preferred stock, par value (usd per share)				$ 0.00001	$ 0.00001	$ 0.00001
Preferred stock, issued (in shares)				0	0
Preferred stock, outstanding (in shares)				0	0
Omnibus Agreement
Sale of Stock [Line Items]
Class of warrant common stock exercise price (usd per share)	$ 0.01
Vesting period	5 years
The Lemonade Foundation | Affiliated entity
Sale of Stock [Line Items]
Contribution to the Lemonade Foundation (in shares)			500,000
Follow-on Offering
Sale of Stock [Line Items]
Common stock sold (in shares)		3,300,000
Net proceeds from sale		$ 525.7
Follow-on Offering, Selling Shareholders
Sale of Stock [Line Items]
Common stock sold (in shares)		1,524,314
Underwriter's option
Sale of Stock [Line Items]
Common stock sold (in shares)		718,647
Net proceeds from sale		$ 114.6