Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Historical Average Claims Ratios, Period, Minimum		5 years
Historical Average Claims Ratios, Period, Maximum		10 years
Hollenfels [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Share of incurred and paid claims	$ 15.3
Share of claims incurred but not reported		$ 5.8