Loss and Loss Adjustment Expense Reserves (Loss and Loss Adjustment Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Loss and Loss Adjustment Expense Reserve
Gross beginning balance	$ 1,357.0	$ 1,137.8	$ 1,350.0	$ 1,054.3
Less beginning reinsurance recoverable on unpaid losses	(147.2)	(92.1)	(161.7)	(80.2)
Net loss and LAE reserves	1,209.8	1,045.7	1,188.3	974.1
Loss and LAE incurred relating to current year losses	170.4	178.4	536.7	511.0
Net (favorable) and unfavorable loss reserve development	(0.4)	7.1	(2.6)	16.3
Total incurred losses and LAE	170.0	185.5	534.1	527.3
Current year losses	(53.0)	(55.9)	(120.2)	(116.5)
Prior year losses	(108.1)	(107.3)	(383.5)	(330.5)
Total loss and LAE payments	(161.1)	(163.2)	(503.7)	(447.0)
Net ending balance	1,218.7	1,068.0	1,218.7	1,068.0
Plus ending reinsurance recoverable on unpaid losses	214.6	101.5	214.6	101.5
Gross ending balance	1,433.3	1,169.5	1,433.3	1,169.5
Star & Shield Insurance Exchange
Loss and Loss Adjustment Expense Reserve
Loss and LAE reserves consolidated — SSIE	0.0	0.0	0.0	13.6
Net (favorable) and unfavorable loss reserve development	$ (0.4)	$ (0.2)	$ (0.8)	$ 2.0