Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Non-Recurring Basis (Detail)

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Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Non-Recurring Basis (Detail) (Non-recurring Basis [Member], USD $)
 6 Months Ended 12 Months Ended
Jun. 30, 2013
Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Unrealized Losses on Non-performing loans held for sale   $ 3,747,000
Unrealized Losses impaired loans 1,343,000 580,000
Unrealized Losses Other real estate owned 7,000 301,000
Significant Observable Inputs with No Active Market with Identical Characteristics [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Non-performing loans held for sale 2,553,000 484,000
Impaired loans 30,444,000 27,844,000
Other real estate owned 900,000 774,000
Significant Unobservable Inputs [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Impaired loans $ 187,000 $ 8,888,000