Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
	Oct. 16, 2009	Dec. 31, 2014 Segment Office Plans	Oct. 16, 2009
Summary Of Significant Accounting Policies [Line Items]
Number of operating business segments		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
Original terms of modified loans		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
Allowance for loan losses look-back period, revised		Rolling twenty quarters
Agreed percentage of losses in loss sharing agreement	80.00%		80.00%
Loss amount with respect to covered assets	26,700,000
Agreed percentage of reimbursement in loss sharing agreement	95.00%
Commercial loans expiration date		Oct. 16, 2014
Goodwill impairment		0
Number of stock-based employee compensation plans		3
Number of offices providing services, CitizensTrust		3
Assets under administration, CitizensTrust		2,410,000,000
Assets under management, CitizensTrust		1,870,000,000
Commercial Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Loss sharing agreement term	5 years
Loss recovery provisions term	8 years
Single-family Residential Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Loss sharing agreement term	10 years
Loss recovery provisions term	10 years
Previously Reported [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for loan losses look-back period, previous		3 years
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
Length of modified debt term		3 months
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
Length of modified debt term		12 months
Loss recoveries on covered assets	$ 144,000,000