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Securities - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Sep. 30, 2013
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]            
Available-for-sale securities transferred to held-to-maturity securities     $ 536,000,000.0      
Unrealized net loss on securities transferred from available-for-sale to held-to-maturity, Gross     $ 13,300,000      
Realized gains on the sale of available-for-sale securities $ 0 $ 246,000     $ 248,000  
Corporate debt securities, callable, amortized cost 61,000,000.0     $ 61,000,000.0    
Corporate debt securities, callable, estimated fair value 58,200,000     58,200,000    
Securities pledged for other debt obligations, at fair value 512,100,000     512,100,000   $ 563,100,000
Debt Securities, Available-for-sale, Realized Loss 0     0    
Reverse Repurchase Agreement            
Debt Securities, Available-for-sale [Line Items]            
Securities pledged for repurchase agreements, at fair value $ 68,800,000     $ 68,800,000   $ 74,100,000