Reinsurance (Cumulative Paid Claims) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cumulative Paid Claims [Line Items]
Cumulative Paid Claims	$ 161.4
Incident Year 2013 [Member]
Cumulative Paid Claims [Line Items]
Cumulative Paid Claims	40.8	$ 40.8	$ 40.8	$ 40.8	$ 38.9
Incident Year 2014 [Member]
Cumulative Paid Claims [Line Items]
Cumulative Paid Claims	39.9	39.9	39.9	$ 38.3
Incident Year 2015 [Member]
Cumulative Paid Claims [Line Items]
Cumulative Paid Claims	33.4	33.4	$ 31.9
Incident Year 2016 [Member]
Cumulative Paid Claims [Line Items]
Cumulative Paid Claims	26.0	$ 24.7
Incident Year 2017 [Member]
Cumulative Paid Claims [Line Items]
Cumulative Paid Claims	$ 21.3