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Investment Securities - Additional Information (Detail) (USD $) | 9 Months Ended | 12 Months Ended |  | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended
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Sep. 30, 2014 Securities | Dec. 31, 2013 Securities | Sep. 30, 2014 Mortgage-backed securities Non-Agency Alt-A residential | Sep. 30, 2014 Debt Securities | Sep. 30, 2013 Debt Securities | Sep. 30, 2014 Debt Securities | Sep. 30, 2013 Debt Securities | Sep. 30, 2014 Non Agency Mortgage Backed Securities | Sep. 30, 2013 Non Agency Mortgage Backed Securities | Sep. 30, 2014 Non Agency Mortgage Backed Securities | Sep. 30, 2013 Non Agency Mortgage Backed Securities | Sep. 30, 2014 Equity Securities | Sep. 30, 2013 Equity Securities | Sep. 30, 2014 Equity Securities | Sep. 30, 2013 Equity Securities
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Held-to-maturity securities in continuous unrealized loss position |  | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Number of securities in an unrealized loss position | 114 | 219 |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of combined depreciation of the combined reported value of the aggregate securities portfolio | 3.57% | 5.06% |  |  |  |  |  |  |  |  |  |  |  |  |
Carrying value of securities pledged | 260,450,000 | 284,770,000 |  |  |  |  |  |  |  |  |  |  |  |  |
OTTI charges incurred |  |  |  | $ 0 | $ 0 | $ 0 | $ 0 | $ 219,000 | $ 0 | $ 705,000 | $ 0 | $ 0 | $ 0 | $ 32,000 | $ 0
Voluntary constant prepayment rate |  |  | 2.50% |  |  |  |  |  |  |  |  |  |  |  |
Constant default rate scenario |  |  | 13.00% |  |  |  |  |  |  |  |  |  |  |  |
Severity rate |  |  | 45.00% |  |  |  |  |  |  |  |  |  |  |  |
Reduced severity rate | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Severity rate reduction period | 27 months |  |  |  |  |  |  |  |  |  |  |  |  |  |

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