Annual report pursuant to Section 13 and 15(d)

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

v3.20.4
Accumulated Other Comprehensive Income (Loss) - Additional Information (Detail) - USD ($)
 12 Months Ended
Jan. 01, 2018
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]        
Net unrealized gains (losses) recorded in comprehensive income   $ 15,300,000 $ 586,000 $ (413,000)
Net gain (loss) on sales of securities   $ 15,712,000 1,295,000 (341,000)
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
Tax Benefit (Expense)        
Accumulated Other Comprehensive Income Loss [Line Items]        
Reduction in tax benefits upon adoption of ASUs $ 546,000     $ 546,000