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Qualifying Debt Subordinated Debt Details (Details) - USD ($)
Dec. 31, 2019
Dec. 31, 2018
Jun. 16, 2016
Jun. 29, 2015
Debt Instrument [Line Items]        
Subordinated Debt $ 319,200,000 $ 299,400,000    
Subordinated Debt [Member] | Subordinated Debentures Maturing July 2056 [Member]        
Debt Instrument [Line Items]        
Debt Instrument, Face Amount $ 175,000,000.0   $ 175,000,000.0  
Debt Issuance Cost     $ 5,500,000  
Debt Instrument, Interest Rate, Stated Percentage     6.25%  
Subordinated Debt [Member] | Subordinated Debentures Maturing July 2025 [Member]        
Debt Instrument [Line Items]        
Debt Instrument, Face Amount       $ 150,000,000.0
Debt Issuance Cost       $ 1,800,000
Debt Instrument, Interest Rate, Stated Percentage 5.00%