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Investment Securities - Additional Information (Detail)
$ in Millions
Mar. 31, 2019
USD ($)
Security
Dec. 31, 2018
USD ($)
Investments, Debt and Equity Securities [Abstract]    
Number of available-for-sale investment securities in the less than twelve month category 4  
Number of available-for-sale investment securities in the twelve month category 22  
Pledged investment securities fair value | $ $ 22.9 $ 23.0