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Investment Securities - Additional Information (Detail)
 3 Months Ended
Mar. 31, 2021
USD ($)
security
Mar. 31, 2020
USD ($)
Dec. 31, 2020
USD ($)
Summary of Investment Holdings [Line Items]      
Accrued interest receivable $ 26,100,000   $ 27,000,000.0
Number of securities in security portfolio | security 1,892    
Number of securities in unrealized loss position | security 280    
Total investment securities - available-for-sale $ 6,724,530,000   5,970,115,000
Unrealized losses 82,422,000   11,385,000
Equity securities, at fair value 2,429,000   2,547,000
Gains on equity securities 100,000 $ 100,000  
Impairments on equity securities without readily determinable fair value 0 0  
Other Assets [Member]      
Summary of Investment Holdings [Line Items]      
Equity securities without readily determinable fair value $ 117,200,000   105,800,000
Pooled trust preferred securities      
Summary of Investment Holdings [Line Items]      
Number of pooled trust preferred securities | security 2    
Total investment securities - available-for-sale $ 8,210,000   7,913,000
Unrealized losses 5,543,000   $ 5,850,000
Other-than-temporary impairment loss $ 0 $ 0