Reserves for Unpaid Losses and Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
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	$ 3.1		$ 4.6	$ 5.4
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense		$ 1.5
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			4.0
Loss and Loss Adjustment Expenses Incurred in 2014 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			4.0
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]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense				6.9
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			0.5
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			1.0	3.4
Loss and Loss Adjustment Expenses Incurred In 2011 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				3.6
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			2.1
Loss And Loss Adjustment Expenses Incurred In 2010 And Prior 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				1.7
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			4.0	3.0
Standard Commercial P & C Business Unit [Member] | Loss and Loss Adjustment Expenses Incurred In 2011 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				3.0
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			0.8	1.9
Workers Compensation Business Unit [Member] | Loss and Loss Adjustment Expenses Incurred in 2014 and 2011 [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			0.8
Workers Compensation Business Unit [Member] | Loss and Loss Adjustment Expenses Incurred in 2013 and 2012 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				1.9
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			1.3	0.7
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			0.5
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense				3.3
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			0.3	0.9
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			0.3	0.5
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			0.7
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense				0.7
Personal 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				3.1
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense			2.0
Personal Segment [Member] | Loss and Loss Adjustment Expenses Incurred in 2014 and Prior 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			$ 2.0
Personal Segment [Member] | 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]
Favorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense				$ 3.1