Fair Value Measurements - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Securities	Dec. 31, 2013 Securities
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 single-issuer trust preferred securities transferred between hierarchy levels	0	4
Change in unrealized gains or losses included in earnings relating to assets still held	13,766	78
Allocated allowance for loan losses	1,179
Fair value of allocated allowance	1,705
Estimated costs to sell	53
Provision for fair value measurements included in allowance for loan losses	756
Carrying amount of OREO	9,685
Written down of OREO	7,119
Fair value of OREO	8,060	19,442
Estimated cost to sell OREO	941
Loss from OREO included in earnings	2,566
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	2,831
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