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Investments (Narrative) (Details) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2015 USD ($) security | Sep. 30, 2014 USD ($) | Dec. 31, 2014 USD ($)
Schedule of Investments [Line Items] |  |  |
Credit-related net investment impairment losses | $ 0 | $ 0 | $ 0
Regional community bank stocks, percent of average trading volumes (less than 0.1%) | 0.10% |  |
Number Of Pooled Trust Preferred Securities | security | 5 |  |
Pooled trust preferred securities, book value | $ 1,800,000 |  |
Pooled trust preferred securities, estimated fair value | $ 1,800,000 |  |
Annual prepayment rate | 1.00% |  | 1.00%
Annual prepayments maturity | 100.00% |  | 100.00%
Additional basis points | 1.50% |  | 1.50%
Carrying value of securities pledged | $ 274,000,000 |  | $ 273,000,000
Held-to-maturity Securities, Transferred Security, at Carrying Value | $ 0 | $ 83,400,000 |
Maximum [Member] |  |  |
Schedule of Investments [Line Items] |  |  |
Equity ownership positions in the community bank holding companies | 4.00% |  |

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