Allowance for Loan Losses - Impaired Financing Receivables - Average Recorded Investment and Interest Income Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	$ 10,395	$ 17,454	$ 10,646	$ 17,655
Impaired financing receivables, Interest Income Recognized, Total	101	143	247	447
Commercial and Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	1,762	4,045	1,943	3,986
Impaired financing receivables, Interest Income Recognized, Total	3	14	37	79
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	4,125	6,996	3,866	7,058
Impaired financing receivables, Interest Income Recognized, Total	62	61	125	187
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	1,992	2,911	2,053	2,976
Impaired financing receivables, Interest Income Recognized, Total	10	14	19	35
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	2,471	3,495	2,752	3,628
Impaired financing receivables, Interest Income Recognized, Total	26	54	66	146
Real Estate Construction [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	40		27
Consumer and Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, Average Recorded Investment, Total	$ 5	$ 7	$ 5	$ 7