Fair Value Measurement - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Fair Value Measurements Disclosure [Line Items]
Derivative instrument maximum maturity period			30 years
Transfers between level 1 and level 2	$ 0		$ 0			$ 0
Loans held for sale, at fair value	9,839,000		9,839,000			0
Transfers between level 2 and level 3	0		0			0
Fair value of the collateral dependent loans, net carrying amount	4,200,000	$ 3,200,000	4,200,000	$ 3,200,000		4,800,000
Specific allowance for collateral dependent loans	644,000	277,000	644,000	277,000		713,000
Increase (decrease) in provision for loan losses	$ (34,000)	(30,000)	(36,000)	439,000
Discount applied to appraisals for estimated selling costs percentage	10.00%
Mortgage servicing rights carried at fair value	$ 215,000	157,000	215,000	157,000		1,100,000
Mortgage servicing rights carried at fair value, valuation allowance	12,000	6,000	12,000	6,000	$ 219,000	58,000	$ 1,000
Net impairment (recovery) reflected in other income	(207,000)	5,000	(46,000)	6,000
Other real estate owned carried at fair value	1,800,000		1,800,000
Other Real Estate Owned Carried At Fair Value, Gross		6,800,000		6,800,000		3,300,000
Valuation allowance related to other real estate owned	1,200,000	3,600,000	1,200,000	3,600,000		$ 1,400,000
Additions charged to expense	42,000	$ 146,000	123,000	$ 438,000
Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due	0		$ 0
Maximum maturity period of short term borrowings			90 days
Minimum [Member]
Fair Value Measurements Disclosure [Line Items]
Increase in fair value	$ 250,000		$ 250,000