Annual report pursuant to Section 13 and 15(d)

Accumulated Other Comprehensive Income (Loss) - Additional Information (Detail)

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Accumulated Other Comprehensive Income (Loss) - Additional Information (Detail) - USD ($)
 12 Months Ended
Jan. 01, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]        
Net gain (loss) on sales of securities   $ 1,295,000 $ (341,000) $ 1,748,000
Net unrealized gains (losses) recorded in comprehensive income   586,000 (413,000) 1,300,000
Accumulated Other Comprehensive Income (Loss)        
Accumulated Other Comprehensive Income Loss [Line Items]        
Adjustment to accumulated other comprehensive income related to adoption of ASU 2016-01 and 2018-02, net of tax $ 17,000   17,000  
Unrealized Gains and Losses on Available for Sale Securities        
Accumulated Other Comprehensive Income Loss [Line Items]        
Reduction of unrealized losses related to securities 529,000   529,000  
Unrealized Gains and Losses on Available for Sale Securities | Reclassification out of Accumulated Other Comprehensive Income        
Accumulated Other Comprehensive Income Loss [Line Items]        
Net gain (loss) on sales of securities   $ 1,300,000 87,000 $ 1,700,000
Tax Benefit (Expense)        
Accumulated Other Comprehensive Income Loss [Line Items]        
Reduction in tax benefits upon adoption of ASUs $ 546,000   $ 546,000