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Securities - Additional Information (Detail) (USD $)
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6 Months Ended | 12 Months Ended |
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Jun. 30, 2013
Securities
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Dec. 31, 2012
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| Investments Debt And Equity Securities [Abstract] | ||
| Carrying value of securities | $ 87,300,000 | $ 79,200,000 |
| Restricted stock investment in FHLB stock | 5,000,000 | 5,000,000 |
| Federal Reserve Bank stock | 471,000 | 471,000 |
| Income tax provision applicable to realized gains | 3,000 | 0 |
| Income tax benefit on realized losses | $ 0 | $ 0 |
| Number of securities in unrealized loss | 60 | |
| Number of securities in continuous loss | 5 |