Reserves for Unpaid Losses and Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 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		$ 7,600	$ 7,000
Unfavorable adjustment to prior years liability for unpaid claims and claims adjustment expense	$ 40,105	7,608
Claims and Claim Adjustment Expenses Incurred Related to Prior Years	40,105	7,608	$ (6,953)
Specialty Commercial Segment [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	40,477	12,502
Standard Commercial Segment [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	(970)	(9,901)
Personal Segment [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	$ 598	$ 5,007