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Reinsurance - Narrative (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Munich Re
Concentration Risk [Line Items]
Concentration Risk, Percentage	9.40%	16.80%
Lloyd's
Concentration Risk [Line Items]
Concentration Risk, Percentage	6.60%	12.80%
Axis Re
Concentration Risk [Line Items]
Concentration Risk, Percentage	2.50%	4.60%

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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