Schedule III - Supplementary Insurance Information (Details) - Property and Casualty Insurance - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplementary Insurance Information
Deferred Policy Acquisition Costs	$ 70,996	$ 68,937	$ 67,329
Future Policy Benefits, Losses, Claims and Loss Expenses	560,321	553,977	482,012
Unearned Premiums	418,033	401,961	390,361
Premium Revenue	755,760	738,164	716,875
Net Investment Income	38,413	40,534	42,303
Benefits, Claims, Losses, and Settlement Expenses	493,433	612,569	476,366
Other Operating Expenses	91,477	75,700	86,497
Premiums Written	766,470	746,180	734,914
Amortization of Deferred Policy Acquisition Costs	$ 141,540	$ 138,239	$ 132,526