Reserves for Unpaid Losses and Loss Adjustment Expenses (Reserve Summary) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross beginning balance	$ 1,350.0	$ 1,054.3	$ 1,000.0
Less beginning reinsurance recoverable on unpaid losses	(161.7)	(80.2)	(107.3)
Net loss and LAE reserves	1,188.3	974.1	892.7
Current Accident Year	712.9	732.0	622.1
Prior Accident Year	(4.0)	92.0	0.0
Total incurred losses and LAE	708.9	824.0	622.1
Loss and LAE paid relating to current year losses	(208.8)	(202.6)	(188.6)
Loss and LAE paid relating to prior year losses	(479.1)	(420.8)	(352.1)
Total loss and LAE payments	(687.9)	(623.4)	(540.7)
Net loss and LAE reserves	1,209.3	1,188.3	974.1
Plus ending reinsurance recoverable on unpaid losses	186.5	161.7	80.2
Gross ending balance	1,395.8	1,350.0	1,054.3
Star & Shield Insurance Exchange [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Loss and LAE reserves consolidated — SSIE	$ 0.0	$ 13.6	$ 0.0