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Employee Benefits - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]      
Number of unearned ESOP shares 31,785 63,570 95,354
Unearned employee stock ownership plan (ESOP) shares, fair value $ 318,000 $ 636,000  
Employee stock owner ship plan expense 328,000 268,000 233,000
Retirement savings 401(k) plan
     
Defined Benefit Plan Disclosure [Line Items]      
Employer 401(k) matching contribution to employee, maximum percentage 4.00%    
Defined contribution plan, contribution 537,000 524,000 539,000
Retirement savings 401(k) plan | Up to 3% of participant contributions
     
Defined Benefit Plan Disclosure [Line Items]      
Percentage of participant contributions 3.00%    
Percentage employer matching contribution 100.00%    
Retirement savings 401(k) plan | 3%-5% of participant contributions
     
Defined Benefit Plan Disclosure [Line Items]      
Percentage employer matching contribution 50.00%    
Retirement savings 401(k) plan | 3%-5% of participant contributions | Minimum
     
Defined Benefit Plan Disclosure [Line Items]      
Percentage of participant contributions 3.00%    
Retirement savings 401(k) plan | 3%-5% of participant contributions | Maximum
     
Defined Benefit Plan Disclosure [Line Items]      
Percentage of participant contributions 5.00%    
Supplemental retirement plan and deferred compensation arrangements
     
Defined Benefit Plan Disclosure [Line Items]      
Defined contribution plan, contribution 675,000 693,000 823,000
ESOP
     
Defined Benefit Plan Disclosure [Line Items]      
Unearned employee stock ownership plan (ESOP) shares, fair value $ 363,000 $ 449,000 $ 887,000