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Investments (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 6 Months Ended |
--- | --- | ---
Jun. 30, 2013 security | Jun. 30, 2012 | Dec. 31, 2012
Schedule of Investments [Line Items] |  |  |
Credit-related net investment impairment losses |  | $ 0.3 |
Pooled trust preferred securities, estimated fair value | 2.5 |  |
Regional community bank stocks, percent of average trading volumes (less than 0.1%) |  | 0.10% |
Number Of Pooled Trust Preferred Securities | 5 |  |
Pooled trust preferred securities, book value | 4.9 |  |
Annual prepayment rate | 1.00% |  |
Annual prepayments maturity | 100.00% |  |
Additional basis points | 1.50% |  |
Carrying value of securities pledged | 231 |  | 228
Minimum [Member] |  |  |
Schedule of Investments [Line Items] |  |  |
Equity ownership positions in the community bank holding companies | 2.00% |  |
Maximum [Member] |  |  |
Schedule of Investments [Line Items] |  |  |
Equity ownership positions in the community bank holding companies | 5.00% |  |
Pooled Bank Trust Preferred Securities [Member] |  |  |
Schedule of Investments [Line Items] |  |  |
Remaining book value |  | $ 3.3 |

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