Reinsurance (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Ceded Credit Risk [Line Items]
Reinsurance Claims Recoverables	$ 257.6	$ 242.0
Claims Recoverable From Retrocessionaires Past Due	$ 3.8	$ 4.0
AM Best, A- Rating [Member]
Ceded Credit Risk [Line Items]
Ceded Credit Risk, Disclosure	“A- (excellent)”	“A- (excellent)”