Revenue - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) obligation	Jun. 30, 2020 USD ($)
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 | $	$ 10.6	$ 10.3	$ 23.9	$ 23.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation, satisfaction period	4 years		4 years