Significant Accounting Policies (Details)	3 Months Ended
Mar. 31, 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%
Period of time over which management fee revenue allocated to administrative services will be recognized (in years)	4 years

Period in which remaining performance obligation is expected to be recognized as revenue, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130556-203045

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84173487&loc=SL51747714-108306

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration