Reinsurance (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Percentage of ceded earned premiums to gross earned premiums	41.00%	38.00%	40.00%	37.00%
Percentage of assumed earned premiums to net earned premiums	29.00%	28.00%	27.00%	29.00%
Reinsurance recoverables	$ 215.4	$ 52.0	$ 349.4	$ 223.8
Program Services [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance recoverables	$ 338.5	$ 373.3	$ 703.5	$ 629.6