Revenue - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) obligation	Dec. 31, 2020 USD ($)	Dec. 31, 2019 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
Indemnity revenue recognized | $	$ 36.9	$ 35.9	$ 33.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Period of time over which indemnity revenue will be recognized	4 years