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Investment Securities - Additional Information (Detail)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
USD ($)
Security
Jun. 30, 2018
USD ($)
Jun. 30, 2019
USD ($)
Security
Jun. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
Investment [Line Items]          
Loss upon acquisition of interest-only GNMA securities $ 7,476 $ 0 $ 7,476 $ 0  
Number of available-for-sale investment securities in the less than twelve month category | Security 0   0    
Number of available-for-sale investment securities in the twelve month category | Security 7   7    
Pledged investment securities fair value $ 22,600   $ 22,600   $ 23,000
Interest-only classes of agency-guaranteed home equity conversion mortgage-backed securities, reported at fair value based on a fair value option election          
Investment [Line Items]          
Loss upon acquisition of interest-only GNMA securities 7,500   7,500    
Interest-only classes of agency-guaranteed home equity conversion mortgage-backed securities $ 17,157   $ 17,157