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Securities - Additional Information (Detail) (USD $) | 9 Months Ended | 12 Months Ended
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Sep. 30, 2013 Contract | Dec. 31, 2012 Contract
Amortized Cost And Fair Value Debt Securities [Abstract] |  |
Number of U.S. agency and mortgage-backed securities | 37 | 12
Number of obligations of state and political subdivisions in an unrealized loss position | 21 | 9
Percentage of investment portfolio | 100.00% | 100.00%
Weighted-average period of re-pricing of portfolio | 5 years 1 month 6 days | 3 years 7 months 6 days
Impairment recognized | $ 0 |

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- Definition Impairment losses related to federal home loan stock. + References No definition available. + Details
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