Reserves for Unpaid Losses and Loss Adjustment Expenses (Narrative) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 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 $ 7,000 $ 5,200  
Unfavorable adjustment to prior years liability for unpaid claims and claims adjustment expense     $ 10,000
Claims and Claim Adjustment Expenses Incurred Related to Prior Years (6,953) (5,203) 9,954
Loss Adjustment Expenses Recognized In 2010 [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     3,300
Loss Adjustment Expenses Recognized In 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   2,400  
Unfavorable adjustment to prior years liability for unpaid claims and claims adjustment expense     1,700
Loss Adjustment Expenses Recognized In 2012 [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 1,100    
Unfavorable adjustment to prior years liability for unpaid claims and claims adjustment expense   4,400 5,000
Loss Adjustment Expenses Recognized In 2013 [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   7,200  
Unfavorable adjustment to prior years liability for unpaid claims and claims adjustment expense 1,500    
Claims and Claim Adjustment Expenses Incurred Related to Prior Years     10,000
Loss Adjustment Expenses Recognized In 2014 [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 7,400    
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     3,700
Claims and Claim Adjustment Expenses Incurred Related to Prior Years (5,400) (4,100)  
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     1,500
Claims and Claim Adjustment Expenses Incurred Related to Prior Years (2,000) (1,900)  
Specialty 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     2,600
Claims and Claim Adjustment Expenses Incurred Related to Prior Years (2,000)    
MGA Commercial Products [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   4,700  
Claims and Claim Adjustment Expenses Incurred Related to Prior Years (200)    
MGA Commercial Products [Member] | Loss Adjustment Expenses Recognized In 2013 [Member]      
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]      
Claims and Claim Adjustment Expenses Incurred Related to Prior Years     16,000
Hallmark Select Business Unit [Member]      
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]      
Claims and Claim Adjustment Expenses Incurred Related to Prior Years   (1,000)  
Hallmark Select Business Unit [Member] | Loss Adjustment Expenses Recognized In 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     2,300
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   900  
Claims and Claim Adjustment Expenses Incurred Related to Prior Years 300    
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   400  
Claims and Claim Adjustment Expenses Incurred Related to Prior Years 800    
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   300  
Claims and Claim Adjustment Expenses Incurred Related to Prior Years 900    
Personal Lines Business Unit [Member]      
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]      
Claims and Claim Adjustment Expenses Incurred Related to Prior Years   $ (2,900)  
Personal Lines Business Unit [Member] | Loss Adjustment Expenses Recognized In 2013 [Member]      
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]      
Claims and Claim Adjustment Expenses Incurred Related to Prior Years     1,800
Personal Lines Business Unit [Member] | Loss Adjustment Expenses Recognized In 2014 [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 $ 2,600    
Excess and Umbrella 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     400
Aircraft Hull [Member] | Loss Adjustment Expenses Recognized In 2012 [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     $ 100