Revenue - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) obligation	Sep. 30, 2020 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Indemnity's management fee rate as a percent of direct and affiliated assumed written premiums of the Exchange (percentage)			25.00%
Performance obligations under subscriber's agreement | obligation			2
Revenue recognized | $	$ 7.8	$ 7.6	$ 31.7	$ 31.0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation, satisfaction period	4 years		4 years