Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Premium Earned:
Gross amount	$ 567,089	$ 524,229	$ 494,643
Ceded to other companies	207,732	170,859	145,562
Assumed from other companies	1,680
Net premiums earned	$ 361,037	$ 353,370	$ 349,081
Percentage of amount assumed to net	0.47%	0.00%	0.00%
Property, Liability and Casualty Insurance Segment [Member]
Premium Earned:
Gross amount	$ 567,089	$ 524,229	$ 494,643
Ceded to other companies	207,732	170,859	145,562
Assumed from other companies	1,680
Net premiums earned	$ 361,037	$ 353,370	$ 349,081
Percentage of amount assumed to net	0.47%	0.00%	0.00%

Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.1)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(c))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-17)
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915

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