Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Direct Amount									$ 2,484,715	$ 2,330,267	$ 2,183,258
Assumed From Other Companies									28,214	23,209	34,653
Ceded to Other Companies									363,357	363,567	365,302
Total Net Premiums Earned	$ 552,753	$ 542,429	$ 531,932	$ 522,458	$ 516,087	$ 507,390	$ 490,309	$ 476,123	$ 2,149,572	$ 1,989,909	$ 1,852,609
Percentage of Amount Assumed to Net									1.00%	1.00%	2.00%
Accident and Health Insurance Segment [Member]
Direct Amount									$ 32	$ 37	$ 44
Assumed From Other Companies									0	0	0
Ceded to Other Companies									0	37	44
Total Net Premiums Earned									$ 32	$ 0	$ 0
Percentage of Amount Assumed to Net									0.00%	0.00%	0.00%
Property and liability insurance [Member]
Direct Amount									$ 2,484,683	$ 2,330,230	$ 2,183,214
Assumed From Other Companies									28,214	23,209	34,653
Ceded to Other Companies									363,357	363,530	365,258
Total Net Premiums Earned									$ 2,149,540	$ 1,989,909	$ 1,852,609
Percentage of Amount Assumed to Net									1.00%	1.00%	2.00%