Fair Value Measurement of Assets and Liabilities - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Fair Value Assets Measured On Recurring Basis
Transfer of loans to loans held for sale			$ 0	$ 27,329,000
Impaired collateral dependent loans, charge-offs	$ 366,000	$ 495,000	3,000,000	3,700,000
Collateral dependent impaired loans, recorded investment	11,200,000		11,200,000
Specific valuation allowance allocations	2,000,000		2,000,000
Reported net carrying amount of impaired loans	9,200,000		$ 9,200,000
Valuation of loan servicing rights, discount rate			8.00%
Net recoveries of impairment charges on its loan servicing rights	48,000	131,000	$ 209,000	273,000
Maximum discount on foreclosed assets			13.40%
Foreclosed assets measured at fair value upon initial recognition	10,100,000
Allowance for loan losses, charge-offs	629,000	1,700,000	$ 1,500,000	3,700,000
Loss due to re-measurement of repossessed assets	1,300,000	799,000	$ 1,800,000	2,700,000
Minimum
Fair Value Assets Measured On Recurring Basis
Valuation of loan servicing rights, prepayment rate			0.00%
Maximum
Fair Value Assets Measured On Recurring Basis
Valuation of loan servicing rights, prepayment rate			23.00%
Significant Unobservable Inputs (Level 3)
Fair Value Assets Measured On Recurring Basis
Discount rate on impaired loans			13.50%
Available-for-sale Securities
Fair Value Assets Measured On Recurring Basis
Changes in unrealized losses on Level 3 securities	$ 0	$ 0	$ 0	$ 0