Reinsurance (Cumulative Incurred Claims) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cumulative Incurred Claims [Line Items]
Cumulative Incurred Claims	$ 162,400,000
Claims Reserve	$ 1,000,000
Cumulative Number Of Reported Claims	159,139
Incident Year 2013 [Member]
Cumulative Incurred Claims [Line Items]
Cumulative Incurred Claims	$ 40,800,000	$ 40,800,000	$ 40,800,000	$ 40,800,000	$ 40,600,000
Claims Reserve	$ 0
Cumulative Number Of Reported Claims	40,350
Incident Year 2014 [Member]
Cumulative Incurred Claims [Line Items]
Cumulative Incurred Claims	$ 39,900,000	39,900,000	39,900,000	$ 39,800,000
Claims Reserve	$ 0
Cumulative Number Of Reported Claims	40,908
Incident Year 2015 [Member]
Cumulative Incurred Claims [Line Items]
Cumulative Incurred Claims	$ 33,400,000	33,400,000	$ 33,100,000
Claims Reserve	$ 0
Cumulative Number Of Reported Claims	32,907
Incident Year 2016 [Member]
Cumulative Incurred Claims [Line Items]
Cumulative Incurred Claims	$ 26,000,000	$ 25,700,000
Claims Reserve	$ 0
Cumulative Number Of Reported Claims	25,212
Incident Year 2017 [Member]
Cumulative Incurred Claims [Line Items]
Cumulative Incurred Claims	$ 22,300,000
Claims Reserve	$ 1,000,000
Cumulative Number Of Reported Claims	19,762