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Summary of Significant Accounting Policies (Details Textual) (USD $) | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |
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Aug. 31, 2012 | May 31, 2012 | Dec. 31, 2011 | Apr. 30, 2004 | Dec. 31, 2003 | Dec. 31, 2012 | Sep. 30, 2012 | Jun. 30, 2012 | Mar. 31, 2012 | Dec. 31, 2011 | Sep. 30, 2011 | Jun. 30, 2011 | Mar. 31, 2011 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010 | Jul. 31, 2011 | Dec. 31, 2009
Summary of significant accounting policies (Textual) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Assets and revenues |  |  |  |  |  |  |  |  |  |  |  |  |  | 99.00% | 99.00% | 99.00% |  |
Decrease in estimated liability |  |  |  |  |  |  |  |  |  | $ 15,200,000 |  |  |  |  |  |  |  |
Decrease in premium tax receivable |  |  |  |  |  |  |  |  |  | 7,500,000 |  |  |  |  |  |  |  |
Change in estimated guaranty fund liability |  |  |  |  |  |  |  |  |  |  | 2,800,000 |  |  |  |  |  |  |
Comprehensive income |  |  |  |  |  | 8,091,000 | 8,570,000 | 3,948,000 | 9,508,000 | 8,046,000 | 6,162,000 | 5,386,000 | 6,537,000 | 30,117,000 | 26,131,000 | 32,057,000 |  |
Decrease in retained earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,385,000
Original maturity of cash equivalent |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 months |  |  |  |
As adjusted to deferred policy acquisition costs |  |  | 16,578,000 |  |  | 18,419,000 |  |  |  | 16,578,000 |  |  |  | 18,419,000 | 16,578,000 |  |  |
Experience rated commission and other operating costs |  |  |  |  |  |  |  |  |  |  |  |  |  | 11,100,000 | 5,700,000 | 9,500,000 |  |
Advertising expenses |  |  |  |  |  |  |  |  |  |  |  |  |  | 444,000 | 421,000 | 413,000 |  |
Premium tax benefit |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,400,000 | 3,300,000 |  |  |
Assessment Related premium Payment period |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 year |  |  |  |
Assessment Related loss Payment period |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 year |  |  |  |
Proceeds from issuance of trust preferred securities |  |  |  | 25,000,000 | 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase of subordinated debt securities |  |  |  | 25,800,000 | 10,300,000 |  |  |  |  |  |  |  |  |  |  |  | 10,300,000 |
Redemption of debt securities | 12,900,000 | 12,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reduction of deferred policy acquisition costs |  |  | 2,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in deferred income tax liabilities |  |  | 800,000 |  |  |  |  |  |  | 800,000 |  |  |  |  | 800,000 |  |  |
Decrease to shareholders' equity |  |  | 1,400,000 |  |  |  |  |  |  | 1,400,000 |  |  |  |  | 1,400,000 |  |  |
Reduction in book value per share |  |  | $ 0.08 |  |  |  |  |  |  | $ 0.08 |  |  |  |  | $ 0.08 |  |  |
As adjusted |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies (Textual) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Comprehensive income |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 26,131,000 | 32,057,000 |  |
As adjusted to deferred policy acquisition costs |  |  | (2,178,000) |  |  |  |  |  |  | (2,178,000) |  |  |  |  | (2,178,000) |  |  |
As Reported [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies (Textual) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Comprehensive income |  |  |  |  |  |  |  |  |  | 8,031,000 | 6,149,000 | 5,360,000 | 6,535,000 |  | 26,075,000 | 32,143,000 |  |
As adjusted to deferred policy acquisition costs |  |  | $ 18,756,000 |  |  |  |  |  |  | $ 18,756,000 |  |  |  |  | $ 18,756,000 |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies (Textual) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term investments maturity period |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 year |  |  |  |
Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies (Textual) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term investments maturity period |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 months |  |  |  |
Other Assets [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies (Textual) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated useful life of assets |  |  |  |  |  |  |  |  |  |  |  |  |  | 7 years |  |  |  |
Other Assets [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies (Textual) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated useful life of assets |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 years |  |  |  |
Land and office building [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies (Textual) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated useful life of assets |  |  |  |  |  |  |  |  |  |  |  |  |  | 39 years |  |  |  |

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