Reinsurance (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Percentage of ceded earned premiums to gross earned premiums	39.00%	38.00%	40.00%	38.00%
Percentage of assumed earned premiums to net earned premiums	27.00%	28.00%	27.00%	28.00%
Reinsurance recoverables	$ 94.4	$ 171.1	$ 443.8	$ 394.9
Program services [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance recoverables	$ 412.7	$ 329.9	$ 1,100.0	$ 959.5