Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Insurance Earned Premiums
Gross Amount	$ 796,366	$ 776,633	$ 747,786
Ceded to Other Companies	70,150	64,288	54,635
Assumed from Other Companies	29,544	25,819	23,724
Net Amount	755,760	738,164	716,875
Property and Casualty Insurance
Insurance Earned Premiums
Gross Amount	796,366	776,633	747,786
Ceded to Other Companies	70,150	64,288	54,635
Assumed from Other Companies	29,544	25,819	23,724
Net Amount	$ 755,760	$ 738,164	$ 716,875
Percentage of Amount Assumed to Net	3.90%	3.50%	3.30%