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Securities - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Sep. 30, 2013
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2013
Investment [Line Items]        
Available-for-sale securities transferred to held-to-maturity securities $ 536,000     $ 536,000
Unrealized net loss on securities reclassified from available-for-sale to held-to-maturity, Gross $ 13,300     $ 13,300
Realized gains on sale of investment securities   $ 0 $ 248  
Corporate debt securities, callable, amortized cost   59,400    
Corporate debt securities, callable, estimated fair value   57,400    
Estimated fair value of securities pledged for deposits and other purposes   475,600 563,100  
Reverse Repurchase Agreements        
Investment [Line Items]        
Estimated fair value of securities pledged for reverse repurchase agreements   $ 81,400 $ 74,100