Reserves for Unpaid Losses and Loss Adjustment Expenses (Narrative) (Details) (USD $) | 3 Months Ended | 6 Months Ended |
In Millions, unless otherwise specified | Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 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 | $5.60 | ' | $6.80 | ' |
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense | ' | 5.4 | ' | 7.4 |
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 | ' | ' | 7.6 | ' |
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 | ' | ' | 2.6 | 2.9 |
Loss and Loss Adjustment Expenses Incurred in 2012 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 |
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 | ' | ' | 2.5 | ' |
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense | ' | ' | ' | 3.2 |
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 | ' | ' | ' | 2.4 |
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 | ' | ' | 0.7 | ' |
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 | ' | ' | ' | 1.1 |
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 | ' | ' | 1.9 | ' |
Unfavorable Adjustment to Prior Years Liability for Unpaid Claims and Claims Adjustment Expense | ' | ' | ' | 1 |
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 | ' | ' | 1.9 | ' |
Personal Lines Business Unit [Member] | Loss and Loss Adjustment Expenses Incurred in 2012 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 |
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 | ' | ' | 1 | 9.3 |
E&S Commercial Umbrella and Excess Liability 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 | ' |
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 | ' | ' | 3.9 | 1.2 |
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 | ' | ' | 3.9 | ' |
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 | ' | ' | ' | 1.2 |
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 | ' | ' | 0.8 | 0.7 |
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 | ' | ' | 0.7 | ' |
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 | ' | ' | 0.2 | ' |
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 | ' | ' | 1.2 | 1 |
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 | ' | ' | $1.20 | ' |