Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions					3 Months Ended
	Jan. 19, 2021	Jan. 14, 2021	Jul. 02, 2020	Feb. 18, 2020	Mar. 31, 2021	Dec. 31, 2020	Jul. 07, 2020
Sale of Stock [Line Items]
Conversion of Convertible Preferred Stock to common stock upon closing of initial public offering (shares)			31,557,107
Common stock, authorized (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 (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 (shares)					0	0
Preferred stock, outstanding (shares)					0	0
Affiliated entity | The Lemonade Foundation
Sale of Stock [Line Items]
Contribution to the Lemonade Foundation (shares)				500,000	500,000
IPO
Sale of Stock [Line Items]
Common stock sold (shares)			12,650,000
Common stock sold, price (usd per share)			$ 29
Net proceeds from sale			$ 335.6
Underwriter's option
Sale of Stock [Line Items]
Common stock sold (shares)		718,647	1,650,000
Net proceeds from sale		$ 114.6
Follow On Offering
Sale of Stock [Line Items]
Common stock sold (shares)		3,300,000
Net proceeds from sale		$ 525.7
Follow On Offering, Selling Shareholders
Sale of Stock [Line Items]
Common stock sold (shares)		1,524,314
Follow On Offering, Selling Shareholders | The Lemonade Foundation
Sale of Stock [Line Items]
Common stock sold (shares)	100,000