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Investment Securities - Textual (Details) - USD ($)
3 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Dec. 31, 2021
Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]        
Debt securities, available-for-sale, transfer to held-to-maturity $ 500,800,000      
Net unrealized gains on securities transferred from available-for-sale to held-to-maturity during the period 918,000      
Available-for-sale, transfer to held-to-maturity, gain (loss) 0      
Held to maturity mortgage backed securities 1,558,202,000   $ 1,530,500,000  
Available for sale mortgage backed securities 7,070,582,000   7,130,861,000  
Held-to-maturity, interest receivable 7,900,000      
Available-for-sale, interest receivable 23,100,000      
Available-for-sale securities 6,640,069,000   7,113,545,000  
Securities valued at less than historical cost, amount $ 5,690,610,000      
Securities valued at less than historical cost (as percent) 85.70%      
Decrease in available-for-sale provision for credit losses $ 0 $ 2,142,000    
Allowance for credit losses on HTM 1,377,000 1,618,000 1,279,000 $ 2,915,000
Securities pledged as collateral 3,660,000,000   3,880,000,000  
Realized gains 37,000 5,500,000    
Realized losses $ (91,000) $ 13,000    
Income tax benefit related to security gains (losses) (as percent) 26.135% 26.135%    
Commercial Mortgage Backed Securities        
Debt Securities, Available-for-sale [Line Items]        
Held to maturity mortgage backed securities $ 4,400,000   4,900,000  
Available for sale mortgage backed securities 1,460,000,000   1,530,000,000  
Residential Mortgage Backed Securities        
Debt Securities, Available-for-sale [Line Items]        
Held to maturity mortgage backed securities 108,100,000   65,500,000  
Available for sale mortgage backed securities 2,700,000,000   2,920,000,000  
State and political subdivisions        
Debt Securities, Available-for-sale [Line Items]        
Held to maturity mortgage backed securities 1,195,744,000   1,210,248,000  
Available for sale mortgage backed securities 1,812,534,000   1,791,097,000  
Available-for-sale securities 1,653,694,000   1,819,658,000  
Securities valued at less than historical cost, amount 1,489,958,000      
Allowance for credit losses on HTM 1,285,000 $ 1,042,000 $ 1,197,000 $ 2,307,000
State and political subdivisions | Other Credit Enhancement or Insurance        
Debt Securities, Available-for-sale [Line Items]        
Held to maturity mortgage backed securities 538,760,000      
Allowance for credit losses on HTM $ 0