Significant Accounting Policies - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 Obligations	Dec. 31, 2017 USD ($)
Revenue, Performance Obligation [Abstract]
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 | Obligations	2
Administrative services
Cash settlements | $		$ 522.3
Primary agent bonus
Agent bonus estimates
Performance period for agent bonuses	36 months
Period of prior year actual underwriting data used to estimate agent bonuses (in years)	2 years
Secondary agent bonus
Agent bonus estimates
Performance period for agent bonuses	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Period of time over which management fee revenue allocated to administrative services will be recognized (in years)	4 years
Software | Minimum
Fixed assets
Estimated useful life	3 years
Software | Maximum
Fixed assets
Estimated useful life	7 years
Equipment | Minimum
Fixed assets
Estimated useful life	3 years
Equipment | Maximum
Fixed assets
Estimated useful life	10 years
Buildings and building improvements | Minimum
Fixed assets
Estimated useful life	20 years
Buildings and building improvements | Maximum
Fixed assets
Estimated useful life	45 years