Reserves for Unpaid Losses and Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense	$ 1.0	$ 0.4	$ 2.8	$ 1.5
Loss and Loss Adjustment Expenses Incurred in 2015 Accident Year [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			5.8
Loss and Loss Adjustment Expenses Incurred in 2014 Accident Year [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense				1.6
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			0.3
Loss And Loss Adjustment Expenses Incurred In 2013 Accident Year [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			2.4	0.6
Loss and Loss Adjustment Expenses Incurred In 2012 Accident Year [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			1.4	0.1
Loss and Loss Adjustment Expenses Incurred in 2011 and Prior Accident Year [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			1.1	0.6
Standard Commercial P & C Business Unit [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			0.7	2.5
Workers Compensation Business Unit [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			3.0	0.4
Specailty Commercial Segment [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			0.4	0.9
MGA Commerical Products [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			1.2
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense				1.1
Commerical Excess Liability [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			0.1	0.3
Medical Professional Liability Products [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			0.2	0.1
General Aviation [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			0.1	0.5
Specialty Personal Lines [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			$ 2.5	$ 1.2