Significant Accounting Policies (Details)	9 Months Ended
	Sep. 30, 2018
Revenue, Performance Obligation [Abstract]
Number of performance obligations recognized by Indemnity acting as attorney-in-fact for the subscribers of the Exchange	2
Indemnity's management fee rate as a percent of premiums written and assumed by the Exchange (as a percent)	25.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
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