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) (Nonrecurring Basis [Member], USD $)
 3 Months Ended 12 Months Ended
Mar. 31, 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 572,000 580,000
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 2,306,000 484,000
Impaired Loans 25,326,000 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 $ 544,000 $ 8,888,000