Revenue - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) obligation	Sep. 30, 2022 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Management fee rate as a percent of direct and affiliated assumed written premiums of the exchange			25.00%
Performance obligations under subscriber's agreement | obligation			2
Revenue recognized that was included in the contract liability at prior year-end | $	$ 7.7	$ 7.4	$ 31.5	$ 30.1
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation, satisfaction period	4 years		4 years