Allowance for Loan Losses - Impaired Financing Receivables - Average Recorded Investment and Interest Income Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	$ 8,665	$ 14,056	$ 9,849	$ 16,362
Impaired financing receivables, Interest Income Recognized, Total	109	116	381	563
Commercial and Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	1,058	2,829	1,680	3,570
Impaired financing receivables, Interest Income Recognized, Total	9	25	54	104
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	3,263	5,115	3,507	6,313
Impaired financing receivables, Interest Income Recognized, Total	39	21	168	208
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	1,870	2,770	1,997	2,913
Impaired financing receivables, Interest Income Recognized, Total	12	(4)	31	31
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	2,450	3,336	2,640	3,559
Impaired financing receivables, Interest Income Recognized, Total	49	74	128	220
Real Estate Construction [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	20		20
Consumer and Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	$ 4	$ 6	$ 5	$ 7