Fair Value Measurement - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value Measurements Disclosure [Line Items]
Derivative instrument maximum maturity period	30 years
Transfers between level 1 and level 2	$ 0		$ 0
Transfers between level 2 and level 3	0		0
Fair value of the collateral dependent loans, net carrying amount	4,500,000	2,700,000	4,800,000
Specific allowance for collateral dependent loans	678,000	959,000	713,000
Increase (decrease) in provision for loan losses	(35,000)	469,000
Discount applied to appraisals for estimated selling costs percentage	10.00%
Mortgage servicing rights, fair amount	1,500,000	103,000	1,100,000
Mortgage servicing rights net recovery/charge	219,000	1,000	58,000
Mortgage servicing rights, Outstanding Amount		104,000
Mortgage servicing rights valuation			(58,000)
Other real estate owned carried at fair value	2,900,000	3,400,000	1,900,000
Valuation allowance related to other real estate owned	1,200,000	3,600,000	1,400,000
Additional expenses related to other real estate owned	80,000	292,000
Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due	0
Maximum maturity period of short term borrowings	90 days
Minimum [Member]
Fair Value Measurements Disclosure [Line Items]
Increase in fair value	$ 250,000