XML 138 R121.htm IDEA: XBRL DOCUMENT v3.22.0.1
Floating Rate Capital Debt - Narrative (Detail) - USD ($)
1 Months Ended 12 Months Ended
Oct. 15, 2021
Apr. 30, 1997
Jan. 31, 1997
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Debt Instrument [Line Items]            
Liquidation amount per security (in usd per share)       $ 1,000    
Repayments of subordinated debt $ 278,800,000     $ 278,800,000 $ 0 $ 0
NTC Capital I Subordinated Debentures            
Debt Instrument [Line Items]            
Floating rate capital securities, issued     $ 150,000,000      
Debt instrument, basis spread on variable rate     0.52%      
Liquidation amount per security (in usd per share)       $ 1,000    
Repayments of subordinated debt 154,900,000          
NTC Capital II Subordinated Debentures            
Debt Instrument [Line Items]            
Floating rate capital securities, issued   $ 120,000,000        
Debt instrument, basis spread on variable rate   0.59%        
Liquidation amount per security (in usd per share)       $ 1,000    
Repayments of subordinated debt $ 123,900,000          
London Interbank Offered Rate (LIBOR) | NTC Capital I Subordinated Debentures            
Debt Instrument [Line Items]            
Debt instrument, basis spread on variable rate       0.605%    
London Interbank Offered Rate (LIBOR) | NTC Capital II Subordinated Debentures            
Debt Instrument [Line Items]            
Debt instrument, basis spread on variable rate       0.679%