Related Party Transactions (Details) $ / shares in Units, $ in Millions				3 Months Ended			6 Months Ended
	Jan. 19, 2021 shares	Jan. 14, 2021 shares	Feb. 18, 2020 shares	Jun. 30, 2021 USD ($) director	Jun. 30, 2020 USD ($)	Mar. 31, 2020 shares	Jun. 30, 2021 USD ($) director $ / shares shares	Jun. 30, 2020 USD ($)
Related Party Transaction [Line Items]
Common shares contribution to the Lemonade Foundation | $							$ 0.0	$ 12.2
Follow On Offering, Selling Shareholders
Related Party Transaction [Line Items]
Common stock sold (shares) | shares		1,524,314
Common Stock
Related Party Transaction [Line Items]
Contribution to the Lemonade Foundation (shares) | shares						500,000
The Lemonade Foundation | Follow On Offering, Selling Shareholders
Related Party Transaction [Line Items]
Common stock sold (shares) | shares	100,000
Affiliated entity | The Lemonade Foundation
Related Party Transaction [Line Items]
Number of shared directors | director				2			2
Contribution to the Lemonade Foundation (shares) | shares			500,000				500,000
Contribution of common stock to related party, fair value (usd per share) | $ / shares							$ 24,360,000
Common shares contribution to the Lemonade Foundation | $							$ 12.2
Affiliated entity | Rental expense
Related Party Transaction [Line Items]
Expenses with related parties | $				$ 0.1	$ 0.1		0.1	0.1
Key stockholder | Travel related expenses
Related Party Transaction [Line Items]
Expenses with related parties | $				$ 0.1	$ 0.1		$ 0.1	$ 0.1