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Securities - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2013
Sep. 30, 2019
Sep. 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 $ 0   $ 0 $ 248,000  
Realized losses on the sale of available-for-sale securities 0     0    
Corporate debt securities, callable, amortized cost 61,000,000.0     61,000,000.0    
Corporate debt securities, callable, estimated fair value 58,300,000     58,300,000    
Securities pledged for other debt obligations, at fair value 488,700,000     488,700,000   $ 563,100,000
Reverse Repurchase Agreement            
Debt Securities, Available-for-sale [Line Items]            
Securities pledged for repurchase agreements, at fair value $ 65,100,000     $ 65,100,000   $ 74,100,000