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Summary of Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2019
USD ($)
Segment
Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]    
Number of operating business segments | Segment 2  
Number of days on which collection of interest on principal is no longer probable 90 days  
Period over which borrower has to demonstrate repayment performance in compliance with restructured terms to take loan out of nonaccrual status 6 months  
Number of days on which charge-offs unsecured consumer loans are recorded 120 days  
Minimum loan amount for credit review process $ 1,000,000.0  
Allowance for loan losses look-back period, revised Rolling 20-quarters  
Goodwill impairment $ 0  
Assets under administration, CitizensTrust 2,860,000,000  
Assets under management, CitizensTrust $ 2,010,000,000.00  
Percentage of PCI loans to Loan Receivable 0.20% 0.20%
Accounting Standards Update 2016-02 [Member]    
Summary Of Significant Accounting Policies [Line Items]    
Operating Lease, Liability, Current $ 20,000,000  
Minimum [Member]    
Summary Of Significant Accounting Policies [Line Items]    
Number of days over which principal or interest payments are past due to consider loans, excluding PCI loans 30 days  
Number of days for which principal or interest payments on loans, excluding PCI loans remain accrual 30 days  
Maximum [Member]    
Summary Of Significant Accounting Policies [Line Items]    
Number of days for which principal or interest payments on loans, excluding PCI loans remain accrual 89 days