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Investments (Tables) | 12 Months Ended
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Dec. 31, 2012
Summary of Investment Holdings [Line Items] |
Gross unrealized gains and losses and the cost and fair value of investments classified as held-to-maturity |
|  | Cost or Amortized Cost |  |  | Gross Unrealized Gains |  |  | Gross Unrealized Losses |  |  | Fair Value |
|  | (In thousands) |
States and political subdivisions |  | $ | 400,687 |  |  | $ | 31,387 |  |  | $ | (106 | ) |  | $ | 431,968 |
Corporate bonds |  |  | 82,824 |  |  |  | 1,565 |  |  |  | (12 | ) |  |  | 84,377 |
Commercial mortgage-backed securities |  |  | 51,529 |  |  |  | 6,433 |  |  |  | — |  |  |  | 57,962 |
U.S. agency-based mortgage-backed securities |  |  | 32,984 |  |  |  | 3,063 |  |  |  | (5 | ) |  |  | 36,042 |
U.S. Treasury securities and obligations of U.S. Government agencies |  |  | 11,034 |  |  |  | 1,721 |  |  |  | — |  |  |  | 12,755 |
Asset-backed securities |  |  | 4,229 |  |  |  | 192 |  |  |  | (176 | ) |  |  | 4,245 |
Totals |  | $ | 583,287 |  |  | $ | 44,361 |  |  | $ | (299 | ) |  | $ | 627,349 |
|  | Cost or Amortized Cost |  |  | Gross Unrealized Gains |  |  | Gross Unrealized Losses |  |  | Fair Value |
|  | (In thousands) |
States and political subdivisions |  | $ | 441,273 |  |  | $ | 29,026 |  |  | $ | (360 | ) |  | $ | 469,939 |
Corporate bonds |  |  | 92,682 |  |  |  | 1,539 |  |  |  | (130 | ) |  |  | 94,091 |
Commercial mortgage-backed securities |  |  | 51,550 |  |  |  | 4,195 |  |  |  | — |  |  |  | 55,745 |
U.S. agency-based mortgage-backed securities |  |  | 46,096 |  |  |  | 4,162 |  |  |  | (44 | ) |  |  | 50,214 |
U.S. Treasury securities and obligations of U.S. Government agencies |  |  | 9,141 |  |  |  | 1,634 |  |  |  | — |  |  |  | 10,775 |
Asset-backed securities |  |  | 5,306 |  |  |  | 17 |  |  |  | (845 | ) |  |  | 4,478 |
Totals |  | $ | 646,048 |  |  | $ | 40,573 |  |  | $ | (1,379 | ) |  | $ | 685,242 |
Gross unrealized gains and losses and the cost and fair value of investments classified as available-for-sale |
|  | Cost or Amortized Cost |  |  | Gross Unrealized Gains |  |  | Gross Unrealized Losses |  |  | Fair Value |
|  | (In thousands) |
Fixed Maturity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
States and political subdivisions |  | $ | 93,362 |  |  | $ | 5,022 |  |  | $ | (142 | ) |  | $ | 98,242 |
Corporate bonds |  |  | 39,211 |  |  |  | 623 |  |  |  | (24 | ) |  |  | 39,810 |
U.S. agency-based mortgage-backed securities |  |  | 11,941 |  |  |  | 5 |  |  |  | (859 | ) |  |  | 11,087 |
Total Fixed Maturity |  |  | 144,514 |  |  |  | 5,650 |  |  |  | (1,025 | ) |  |  | 149,139 |
Equity securities |  |  | 7,000 |  |  |  | 451 |  |  |  | (685 | ) |  |  | 6,766 |
Totals |  | $ | 151,514 |  |  | $ | 6,101 |  |  | $ | (1,710 | ) |  | $ | 155,905 |
|  | Cost |  |  | Gross Unrealized Gains |  |  | Gross Unrealized Losses |  |  | Fair Value |
|  | (In thousands) |
Fixed Maturity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
States and political subdivisions |  | $ | 55,275 |  |  | $ | 2,488 |  |  | $ | (1 | ) |  | $ | 57,762 |
Corporate bonds |  |  | 42,802 |  |  |  | 411 |  |  |  | (233 | ) |  |  | 42,980 |
Total Fixed Maturity |  |  | 98,077 |  |  |  | 2,899 |  |  |  | (234 | ) |  |  | 100,742 |
Equity securities |  |  | 11,776 |  |  |  | 661 |  |  |  | (197 | ) |  |  | 12,240 |
Totals |  | $ | 109,853 |  |  | $ | 3,560 |  |  | $ | (431 | ) |  | $ | 112,982 |
A summary of the Company's realized gains and losses on sales, calls or redemptions of investments |
|  | Fixed Maturity Securities Available for Sale |  |  | Equity Securities |  |  | Other |  |  | Total |
|  | (In thousands) |
Year ended December 31, 2012 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales |  | $ | 22,363 |  |  | $ | 10,777 |  |  | $ | — |  |  | $ | 33,140 |
Gross realized investment gains |  | $ | 1,555 |  |  | $ | 1,186 |  |  | $ | — |  |  | $ | 2,741 |
Gross realized investment (losses) |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |
Net realized investment gain |  |  | 1,555 |  |  |  | 1,186 |  |  |  | — |  |  |  | 2,741 |
Other, including gains on calls and redemptions |  |  | 15 |  |  |  | — |  |  |  | 223 |  |  |  | 238 |
Net realized investment gains |  | $ | 1,570 |  |  | $ | 1,186 |  |  | $ | 223 |  |  | $ | 2,979 |
Year ended December 31, 2011 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales |  | $ | 21,560 |  |  | $ | 14,769 |  |  | $ | — |  |  | $ | 36,329 |
Gross realized investment gains |  | $ | 815 |  |  | $ | 1,621 |  |  | $ | — |  |  | $ | 2,436 |
Gross realized investment (losses) |  |  | — |  |  |  | (98 | ) |  |  | (1 | ) |  |  | (99 | )
Net realized investment gain |  |  | 815 |  |  |  | 1,523 |  |  |  | (1 | ) |  |  | 2,337 |
Impairments |  |  | — |  |  |  | — |  |  |  | (169 | ) |  |  | (169 | )
Other, including gains on calls and redemptions |  |  | — |  |  |  | — |  |  |  | 60 |  |  |  | 60 |
Net realized investment gains |  | $ | 815 |  |  | $ | 1,523 |  |  | $ | (110 | ) |  | $ | 2,228 |
Year ended December 31, 2010 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales |  | $ | 15,462 |  |  | $ | 14,695 |  |  | $ | — |  |  | $ | 30,157 |
Gross realized investment gains |  | $ | — |  |  | $ | 2,650 |  |  | $ | — |  |  | $ | 2,650 |
Gross realized investment (losses) |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |
Net realized investment gain |  |  | — |  |  |  | 2,650 |  |  |  | — |  |  |  | 2,650 |
Impairments |  |  | — |  |  |  | (693 | ) |  |  | — |  |  |  | (693 | )
Other, including gains on calls and redemptions |  |  | 411 |  |  |  | — |  |  |  | 81 |  |  |  | 492 |
Net realized investment gains |  | $ | 411 |  |  | $ | 1,957 |  |  | $ | 81 |  |  | $ | 2,449 |
Major categories of the Company's net investment income |
|  | Year Ended December 31, |
| 2012 |  |  | 2011 |  |  | 2010 |
|  | (In thousands) |
Gross investment income: |  |  |  |  |  |  |  |  |  |  |  |
Fixed maturity securities |  | $ | 27,167 |  |  | $ | 26,769 |  |  | $ | 26,571 |
Short-term investments and cash and cash equivalents |  |  | 489 |  |  |  | 590 |  |  |  | 819 |
Equity securities |  |  | 446 |  |  |  | 181 |  |  |  | 71 |
Total gross investment income |  |  | 28,102 |  |  |  | 27,540 |  |  |  | 27,461 |
Investment expenses |  |  | (1,084 | ) |  |  | (1,200 | ) |  |  | (1,219 | )
Net investment income |  | $ | 27,018 |  |  | $ | 26,340 |  |  | $ | 26,242 |
Investment securities continuous unrealized loss position |
|  | As of December 31, 2012 |
|  | Less Than 12 Months |  |  | 12 Months or Greater |  |  | Total |
|  | Fair Value of Investments with Unrealized Losses |  |  | Gross Unrealized Losses |  |  | Fair Value of Investments with Unrealized Losses |  |  | Gross Unrealized Losses |  |  | Fair Value of Investments with Unrealized Losses |  |  | Gross Unrealized Losses |
|  | (in thousands) |
Held-to-Maturity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 10,734 |  |  | $ | 12 |  |  | $ | — |  |  | $ | — |  |  | $ | 10,734 |  |  | $ | 12 |
States and political subdivisions |  |  | 11,913 |  |  |  | 106 |  |  |  | — |  |  |  | — |  |  |  | 11,913 |  |  |  | 106 |
U.S. agency-based mortgage-backed securities |  |  | 117 |  |  |  | — |  |  |  | 68 |  |  |  | 5 |  |  |  | 185 |  |  |  | 5 |
Asset-backed securities |  |  | — |  |  |  | — |  |  |  | 2,277 |  |  |  | 176 |  |  |  | 2,277 |  |  |  | 176 |
Total held-to-maturity securities |  |  | 22,764 |  |  |  | 118 |  |  |  | 2,345 |  |  |  | 181 |  |  |  | 25,109 |  |  |  | 299 |
Available-for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 6,411 |  |  | $ | 24 |  |  | $ | — |  |  | $ | — |  |  | $ | 6,411 |  |  | $ | 24 |
States and political subdivisions |  |  | 6,281 |  |  |  | 142 |  |  |  | — |  |  |  | — |  |  |  | 6,281 |  |  |  | 142 |
U.S. agency-based mortgage-backed securities |  |  | 10,919 |  |  |  | 859 |  |  |  | — |  |  |  | — |  |  |  | 10,919 |  |  |  | 859 |
Equity Securities |  |  | 4,186 |  |  |  | 685 |  |  |  | — |  |  |  | — |  |  |  | 4,186 |  |  |  | 685 |
Total available-for-sale securities |  |  | 27,797 |  |  |  | 1,710 |  |  |  | — |  |  |  | — |  |  |  | 27,797 |  |  |  | 1,710 |
Total |  | $ | 50,561 |  |  | $ | 1,828 |  |  | $ | 2,345 |  |  | $ | 181 |  |  | $ | 52,906 |  |  | $ | 2,009 |
|  | As of December 31, 2011 |
|  | Less Than 12 Months |  |  | 12 Months or Greater |  |  | Total |
|  | Fair Value of Investments with Unrealized Losses |  |  | Gross Unrealized Losses |  |  | Fair Value of Investments with Unrealized Losses |  |  | Gross Unrealized Losses |  |  | Fair Value of Investments with Unrealized Losses |  |  | Gross Unrealized Losses |
|  | (in thousands) |
Held-to-Maturity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 23,063 |  |  | $ | 130 |  |  | $ | — |  |  | $ | — |  |  | $ | 23,063 |  |  | $ | 130 |
States and political subdivisions |  |  | 2,291 |  |  |  | 3 |  |  |  | 5,718 |  |  |  | 357 |  |  |  | 8,009 |  |  |  | 360 |
U.S. agency-based mortgage-backed securities |  |  | — |  |  |  | — |  |  |  | 1,012 |  |  |  | 44 |  |  |  | 1,012 |  |  |  | 44 |
Asset-backed securities |  |  | 545 |  |  |  | 15 |  |  |  | 3,880 |  |  |  | 830 |  |  |  | 4,425 |  |  |  | 845 |
Total held-to-maturity securities |  |  | 25,899 |  |  |  | 148 |  |  |  | 10,610 |  |  |  | 1,231 |  |  |  | 36,509 |  |  |  | 1,379 |
Available-for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 14,301 |  |  | $ | 233 |  |  | $ | — |  |  | $ | — |  |  | $ | 14,301 |  |  | $ | 233 |
States and political subdivisions |  |  | 222 |  |  |  | 1 |  |  |  | — |  |  |  | — |  |  |  | 222 |  |  |  | 1 |
Equity Securities |  |  | 2,789 |  |  |  | 197 |  |  |  | — |  |  |  | — |  |  |  | 2,789 |  |  |  | 197 |
Total available-for-sale securities |  |  | 17,312 |  |  |  | 431 |  |  |  | — |  |  |  | — |  |  |  | 17,312 |  |  |  | 431 |
Total |  | $ | 43,211 |  |  | $ | 579 |  |  | $ | 10,610 |  |  | $ | 1,231 |  |  | $ | 53,821 |  |  | $ | 1,810 |
Total held-to-maturity securities [Member] |
Summary of Investment Holdings [Line Items] |
Summary of the cost or amortized cost and fair value of investments in fixed maturity securities, by contractual maturity |
|  | Cost or Amortized Cost |  |  | Fair Value |
|  | (In thousands) |
Maturity: |  |  |  |  |  |  |  |
Due in 2013 |  | $ | 81,159 |  |  | $ | 81,897 |
In 2014 through 2017 |  |  | 147,800 |  |  |  | 156,272 |
In 2018 through 2022 |  |  | 138,680 |  |  |  | 154,343 |
After 2022 |  |  | 126,906 |  |  |  | 136,588 |
U.S. agency-based mortgage-backed securities |  |  | 32,984 |  |  |  | 36,042 |
Commercial mortgage-backed securities |  |  | 51,529 |  |  |  | 57,962 |
Asset-backed securities |  |  | 4,229 |  |  |  | 4,245 |
Totals |  | $ | 583,287 |  |  | $ | 627,349 |
Total available-for-sale securities [Member] |
Summary of Investment Holdings [Line Items] |
Summary of the cost or amortized cost and fair value of investments in fixed maturity securities, by contractual maturity |
|  | Cost or Amortized Cost |  |  | Fair Value |
|  | (In thousands) |
Maturity: |  |  |  |  |  |  |  |
Due in 2013 |  | $ | 7,239 |  |  | $ | 7,223 |
In 2014 through 2017 |  |  | 24,641 |  |  |  | 25,003 |
In 2018 through 2022 |  |  | 18,708 |  |  |  | 19,342 |
After 2021 |  |  | 81,985 |  |  |  | 86,484 |
U.S. agency-based mortgage-backed securities |  |  | 11,941 |  |  |  | 11,087 |
Totals |  | $ | 144,514 |  |  | $ | 149,139 |

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