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Securities Held-to-Maturity - Schedule of Securities Held-to-Maturity (Detail) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]    
Federal agency debt instruments (amortized cost) $ 20,159 $ 20,180
Federal Agency [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Federal agency debt instruments (amortized cost) $ 20,159 $ 20,180