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Concentration of Operations - Net Premiums Earned for the Top Ten States (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
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Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned | $ 87,377 | $ 85,118 | $ 82,749 | $ 90,912 | $ 92,097 | $ 89,918 | $ 90,728 | $ 95,961 | $ 346,156 | $ 368,704 | $ 375,894
Premium earned percentage |  |  |  |  |  |  |  |  | 100.00% | 100.00% | 100.00%
Georgia [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 40,801 | $ 38,168 | $ 40,497
Premium earned percentage |  |  |  |  |  |  |  |  | 11.80% | 10.40% | 10.80%
Florida [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 34,615 | $ 29,051 | $ 24,792
Premium earned percentage |  |  |  |  |  |  |  |  | 10.00% | 7.90% | 6.60%
Pennsylvania [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 32,931 | $ 39,460 | $ 36,294
Premium earned percentage |  |  |  |  |  |  |  |  | 9.50% | 10.70% | 9.70%
Louisiana [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 25,422 | $ 30,426 | $ 38,874
Premium earned percentage |  |  |  |  |  |  |  |  | 7.30% | 8.30% | 10.30%
Illinois [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 22,169 | $ 25,796 | $ 23,285
Premium earned percentage |  |  |  |  |  |  |  |  | 6.40% | 7.00% | 6.20%
North Carolina [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 18,388 | $ 20,784 | $ 20,062
Premium earned percentage |  |  |  |  |  |  |  |  | 5.30% | 5.60% | 5.30%
Virginia [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 16,298 | $ 16,599 | $ 15,656
Premium earned percentage |  |  |  |  |  |  |  |  | 4.70% | 4.50% | 4.20%
Minnesota [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 13,968 | $ 15,130 | $ 14,618
Premium earned percentage |  |  |  |  |  |  |  |  | 4.00% | 4.10% | 3.90%
Wisconsin [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 13,790 | $ 13,544 | $ 11,203
Premium earned percentage |  |  |  |  |  |  |  |  | 4.00% | 3.70% | 3.00%
South Carolina [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 13,327 | $ 13,897 | $ 12,955
Premium earned percentage |  |  |  |  |  |  |  |  | 3.90% | 3.80% | 3.40%
All Others [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule Of Premiums Earned Net By Segment [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 114,447 | $ 125,849 | $ 137,658
Premium earned percentage |  |  |  |  |  |  |  |  | 33.10% | 34.00% | 36.60%

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- Definition Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned. + References 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 + Details
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