Fair Value Measurements - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2015 Securities	Dec. 31, 2014 Securities	Mar. 31, 2014
Fair Value Measurements Disclosure [Line Items]
Percentage of securities using market-based information	99.90%
Percentage of securities using model-based techniques	0.10%
Minimum corporation reserves for commercial loan	$ 500
Number of securities transferred between hierarchy levels	0	0
Impaired loans, carrying amount	67,919	69,450
Allocated allowance for loan losses	2,181
Fair value of allocated allowance	883
Estimated costs to sell	124
Provision for fair value measurements included in allowance for loan losses	1,002
Carrying amount of OREO	2,501
Written down of OREO	2,140
Fair value of OREO	2,410
Estimated cost to sell OREO	270
Loss from OREO included in earnings	361
Short-term borrowings approximate fair value for amounts that mature, days, less than	90 days
Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements Disclosure [Line Items]
Impaired loans, carrying amount	2,940
Allocated allowance for loan losses	883	1,705
Fair value of OREO	2,410	8,060
Assets Still Held [Member]
Fair Value Measurements Disclosure [Line Items]
Change in unrealized gains or losses included in earnings relating to assets still held	$ 0		$ 0