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v3.8.0.1

Segment Information (Revenue From Continuing Operations by Segment) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
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
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned | $ 590,088 | $ 572,055 | $ 568,030 | $ 560,854 | $ 552,753 | $ 542,429 | $ 531,932 | $ 522,458 | $ 2,291,027 | $ 2,149,572 | $ 1,989,909
Other income | 2,190 | 1,994 | 3,291 | 3,241 | 1,863 | 2,199 | 3,868 | 951 | 10,716 | 8,881 | 7,456
Net investment income | 42,587 | 40,446 | 41,430 | 37,419 | 35,428 | 33,375 | 31,182 | 30,769 | 161,882 | 130,754 | 121,316
Realized investment gains (losses) |  |  |  |  |  |  |  |  | 6,359 | (4,937) | 13,171
Total investment revenues |  |  |  |  |  |  |  |  | 168,241 | 125,817 | 134,487
Total revenues | $ 633,737 | $ 621,293 | $ 614,485 | $ 600,469 | $ 582,358 | $ 581,691 | $ 568,747 | $ 551,474 | 2,469,984 | 2,284,270 | 2,131,852
Miscellaneous Income [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Other income |  |  |  |  |  |  |  |  | 10,716 | 8,881 | 7,456
Standard Commercial Lines [Member] | Commercial Automobile [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 442,818 | 398,942 | 358,909
Standard Commercial Lines [Member] | Workers Compensation [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 317,982 | 308,233 | 290,075
Standard Commercial Lines [Member] | General Liability [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 569,217 | 527,859 | 483,291
Standard Commercial Lines [Member] | Commercial Property [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 311,932 | 293,438 | 269,022
Standard Commercial Lines [Member] | Business Owners' Policies [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 100,266 | 97,754 | 93,428
Standard Commercial Lines [Member] | Bonds Segment [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 29,086 | 23,227 | 20,350
Standard Commercial Lines [Member] | Other Commercial [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 17,198 | 16,030 | 14,367
Standard Commercial Lines [Member] | Miscellaneous Income [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 9,488 | 7,782 | 6,343
Standard Commercial Lines [Member] | Total Standard Commercial Lines [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 1,797,987 | 1,673,265 | 1,535,785
Standard Personal Lines [Member] | Miscellaneous Income [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 1,228 | 1,098 | 1,113
Standard Personal Lines [Member] | Personal Automobile [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 153,147 | 142,876 | 146,784
Standard Personal Lines [Member] | Homeowners [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 129,699 | 130,973 | 134,382
Standard Personal Lines [Member] | Other Personal [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 6,855 | 6,758 | 6,968
Standard Personal Lines [Member] | Standard Personal Lines [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 290,929 | 281,705 | 289,247
E&S Lines [Member] | General Liability [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 157,366 | 151,638 | 126,064
E&S Lines [Member] | Commercial Property [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 55,461 | 51,844 | 46,269
E&S Lines [Member] | Miscellaneous Income [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Other income |  |  |  |  |  |  |  |  | 0 | 1 | 0
E&S Lines [Member] | Total E&S Lines [Member] |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | $ 212,827 | $ 203,483 | $ 172,333

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