Allowance for Loan Losses - Impaired Financing Receivables - Average Recorded Investment and Interest Income Recognized (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	$ 14,055	$ 20,775	$ 16,363	$ 23,048
Impaired financing receivables, Interest Income Recognized, Total	116	61	563	881
Commercial and Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	2,829	4,504	3,570	4,984
Impaired financing receivables, Interest Income Recognized, Total	25	25	104	156
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	7,884	11,237	9,227	12,328
Impaired financing receivables, Interest Income Recognized, Total	17	29	239	438
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	3,336	4,773	3,559	5,324
Impaired financing receivables, Interest Income Recognized, Total	74	18	220	287
Real Estate Construction [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	0	240	0	377
Impaired financing receivables, Interest Income Recognized, Total	0	(11)	0	0
Consumer and Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	6	21	7	35
Impaired financing receivables, Interest Income Recognized, Total	$ 0	$ 0	$ 0	$ 0