Allowance for Loan Losses - Impaired Financing Receivables - Average Recorded Investment and Interest Income Recognized (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	$ 11,033	$ 18,668
Impaired financing receivables, Interest Income Recognized, Total	146	304
Commercial and Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	2,303	4,310
Impaired financing receivables, Interest Income Recognized, Total	34	65
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	3,752	7,512
Impaired financing receivables, Interest Income Recognized, Total	63	126
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	2,123	3,057
Impaired financing receivables, Interest Income Recognized, Total	9	21
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	2,830	3,782
Impaired financing receivables, Interest Income Recognized, Total	40	92
Real Estate Construction [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	20
Consumer and Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	$ 5	$ 7