Fair Value Measurement of Assets and Liabilities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value, unobservable inputs, quantitative information for assets measured on non-recurring basis, impaired loans non-current appraisal discount percentage	6.10%
Impaired collateral dependent loans, charge-offs	$ 17,700,000	$ 16,900,000
Collateral dependent impaired loans, recorded investment	76,900,000	74,300,000
Specific valuation allowance allocations	11,700,000	7,400,000
Reported net carrying amount of impaired loans	65,200,000	66,900,000
Foreclosed assets measured at fair value upon initial recognition	33,300,000	15,900,000
Allowance for loan losses, charge-offs	6,300,000	3,900,000
Loss due to re-measurement of foreclosed assets at fair value	1,500,000	1,300,000
Loan servicing rights [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation of loan servicing rights, discount rate	8.00%
Net impairment charges	$ 376,000	$ 1,500,000
Loan servicing rights [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation of loan servicing rights, prepayment rate	6.00%
Loan servicing rights [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation of loan servicing rights, prepayment rate	26.00%