Related Party Transactions (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023 USD ($) director employee	Sep. 30, 2022 USD ($) employee	Sep. 30, 2023 USD ($) employee director $ / shares shares	Sep. 30, 2022 USD ($) employee	Dec. 31, 2021 shares	Dec. 31, 2020 shares	Dec. 31, 2022 USD ($)
Related Party Transaction [Line Items]
Due from related party	$ 67,600,000		$ 67,600,000				$ 75,200,000
Outstanding amounts due	$ 93,100,000		$ 93,100,000				$ 84,500,000
Immediate Family Member of Management or Principal Owner
Related Party Transaction [Line Items]
Number of stockholders | employee	1	1	1	1
Travel expense (less than)	$ 100,000	$ 100,000	$ 100,000	$ 100,000
Follow-on Offering, Selling Shareholders
Related Party Transaction [Line Items]
Common stock sold (in shares) | shares					1,524,314
Related Party
Related Party Transaction [Line Items]
Number of shared directors | director	2		2
Contribution to the Lemonade Foundation (in shares) | shares			500,000
Contribution of common stock to related party, fair value (usd per share) | $ / shares			$ 24.36
Due from related party	$ 0		$ 0
Outstanding amounts due	$ 0		$ 0
Related Party | Follow-on Offering, Selling Shareholders
Related Party Transaction [Line Items]
Common stock sold (in shares) | shares						100,000