Reserves for Unpaid Losses and Loss Adjustment Expenses (Narrative) (Details) (USD $) | 3 Months Ended | 9 Months Ended |
In Millions, unless otherwise specified | Sep. 30, 2014 | Sep. 30, 2013 | Sep. 30, 2014 | Sep. 30, 2013 |
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 | ' | ' | $5.40 | ' |
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense | 1.5 | 0.5 | ' | 8 |
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 | ' |
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 | ' | ' | 3.4 | 5 |
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 | ' |
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense | ' | ' | ' | 2.4 |
Loss and Loss Adjustment Expenses Incurred in 2010 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 | ' | ' | ' | 1.6 |
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 | ' |
Loss and Loss Adjustment Expenses Incurred in 2009 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 |
Personal Lines 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 | ' | ' | 3.1 | ' |
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense | ' | ' | ' | 1.5 |
Personal Lines Business Unit [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 | ' |
Personal Lines Business Unit [Member] | 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 | ' | ' | ' | 1.5 |
E & S Commercial Business Unit [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 | ' | ' | 3.3 | 11.7 |
E & S Commercial Business Unit [Member] | Loss And Loss Adjustment Expenses Incurred In 2012, 2011 and 2010 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 | ' | ' | ' | 11.7 |
Standard Commercial 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 | 2.4 |
Standard Commercial 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 | ' |
Standard Commercial Business Unit [Member] | Loss and Loss Adjustment Expenses Incurred in 2010 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 | ' | ' | ' | 2.4 |
Hallmark Select 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 | 1.6 |
Hallmark Select Business Unit [Member] | 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 | ' | ' | ' | 1.6 |
General Aviation [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 | ' | ' | 0.7 | ' |
Hallmark Select 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 | ' | ' | 0.9 | ' |
Hallmark Select Professional Medical 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 | ' | ' | 0.5 | ' |
Workers Compensation Risks [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 | 1.2 |
Workers Compensation Risks [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 | ' |
Workers Compensation Risks [Member] | Loss And Loss Adjustment Expenses Incurred In 2012 and 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 | ' | ' | ' | $1.20 |