Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended
	Oct. 16, 2009	Mar. 31, 2013 Plans	Mar. 31, 2012	Dec. 31, 2012
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
Maximum loan amount for credit review process		$ 1,000,000
Agreed percentage of loss in loss sharing agreement	80.00%
Loss recoveries on covered assets	144,000,000
Loss amount with respect to covered assets	26,700,000
Agreed percentage of reimbursement in loss reimburse agreement	95.00%
Goodwill impairment		0
Goodwill		55,097,000		55,097,000
Core deposit and premium		2,950,000		3,389,000
Accumulated amortization		29,000,000
Amortization of intangible assets		438,000	816,000
Estimated amortization expense remainder of 2013		689,000
Estimated amortization expense for 2014		475,000
Estimated amortization expense for 2015		437,000
Estimated amortization expense for 2016		395,000
Estimated amortization expense for 2017		366,000
Estimated amortization expense from 2018 to 2019		$ 589,000
Approximately weighted average remaining life of intangible assets		2 years 1 month 6 days
Number of stock-based compensation plans		3
Commercial Loans [Member]
Loss sharing agreement term	5 years
Loss recovery provision term	8 years
Single Family Residential Loans [Member]
Loss sharing agreement term	10 years
Loss recovery provision term	10 years
Minimum [Member]
Number of days over which principal or interest payment are past due to consider non-covered loans		30 days
Number of days for which principal or interest payment on non-covered loans remain accrual		30 days
Length of modified debt term		3 months
Maximum [Member]
Number of days for which principal or interest payment on non-covered loans remain accrual		89 days
Length of modified debt term		12 months