Loss and Loss Adjustment Expense Reserves (Loss and Loss Adjustment Expense) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Insurance Loss Reserves [Abstract]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0.0	$ 7.3
Gross beginning balance	1,395.8	1,350.0
Less beginning reinsurance recoverable on unpaid losses	(186.5)	(161.7)
Net loss and LAE reserves	1,209.3	1,188.3
Loss and LAE incurred relating to current year losses	161.2	169.8
Net (favorable) and unfavorable loss reserve development	(0.1)	(1.9)
Total incurred losses and LAE	161.1	167.9
Current year losses	(23.1)	(23.3)
Prior year losses	(148.6)	(164.0)
Total loss and LAE payments	(171.7)	(187.3)
Net ending balance	1,198.7	1,168.9
Plus ending reinsurance recoverable on unpaid losses	150.9	141.7
Gross ending balance	$ 1,349.6	$ 1,310.6