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Segment Information (Gross Premiums Earned by Product) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Premiums ceded |  |  |  |  |  |  |  |  | $ 101,510 | $ 68,879 | $ 41,514
Net premiums earned | $ 164,874 | $ 182,085 | $ 175,293 | $ 171,899 | $ 174,670 | $ 177,028 | $ 176,303 | $ 171,730 | 694,149 | 699,731 | 527,919
Specialty Property and Casualty [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 443,313 | 492,733 | 527,919
Premiums ceded to Lloyd's Syndicate |  |  |  |  |  |  |  |  | 14,400 | 4,200 |
Workers Compensation [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 213,161 | 194,540 | 0
Lloyds Syndicate [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 37,675 | 12,458 | 0
Operating Segments [Member] | Specialty Property and Casualty [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Premiums ceded |  |  |  |  |  |  |  |  | 84,805 | 50,319 | 41,514
Net premiums earned |  |  |  |  |  |  |  |  | 443,313 | 492,733 | 527,919
Operating Segments [Member] | Workers Compensation [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Premiums ceded |  |  |  |  |  |  |  |  | 25,122 | 21,793 | 0
Net premiums earned |  |  |  |  |  |  |  |  | 213,161 | 194,540 | 0
Operating Segments [Member] | Lloyds Syndicate [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Premiums ceded |  |  |  |  |  |  |  |  | 5,942 | 971 | 0
Net premiums earned |  |  |  |  |  |  |  |  | 37,675 | 12,458 | 0
Operating Segments [Member] | Healthcare Professional Liability [Member] | Specialty Property and Casualty [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Gross premiums earned |  |  |  |  |  |  |  |  | 463,599 | 477,031 | 507,222
Operating Segments [Member] | Legal Professional Liability [Member] | Specialty Property and Casualty [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Gross premiums earned |  |  |  |  |  |  |  |  | 28,234 | 28,278 | 27,162
Operating Segments [Member] | Medical Technology and Life Sciences Product Liability [Member] | Specialty Property and Casualty [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Gross premiums earned |  |  |  |  |  |  |  |  | 34,838 | 35,913 | 33,242
Operating Segments [Member] | Other Premiums [Member] | Specialty Property and Casualty [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Gross premiums earned |  |  |  |  |  |  |  |  | 1,447 | 1,830 | 1,807
Operating Segments [Member] | Workers' Compensation Traditional Business [Member] | Workers Compensation [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Gross premiums earned |  |  |  |  |  |  |  |  | 172,115 | 160,717 | 0
Operating Segments [Member] | Workers' Compensation Alternative Market Business [Member] | Workers Compensation [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Gross premiums earned |  |  |  |  |  |  |  |  | 66,168 | 55,616 | 0
Operating Segments [Member] | Property, Liability and Casualty Insurance Product Line [Member] | Lloyds Syndicate [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Gross premiums earned |  |  |  |  |  |  |  |  | $ 43,617 | $ 13,429 | $ 0

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