Allowance for Loan Losses - Impaired Financing Receivables - Recorded Investment and Unpaid Principal Balances (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	$ 9,132	$ 8,718
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	11,376	10,142
Impaired financing receivables, with no related allowance recorded, Related Allowance
Impaired financing receivables, with an allowance recorded, Recorded Investment	3,349	9,339
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	5,196	10,954
Impaired financing receivables, with an allowance recorded, Related Allowance	1,618	2,509
Impaired financing receivables, Recorded Investment, Total	12,481	18,057
Impaired financing receivables, Unpaid Principal Balance, Total	16,572	21,096
Impaired financing receivables, Related Allowance, Total	1,618	2,509
Commercial and Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	1,379	1,525
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	1,504	1,657
Impaired financing receivables, with no related allowance recorded, Related Allowance
Impaired financing receivables, with an allowance recorded, Recorded Investment	940	2,344
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	1,056	2,437
Impaired financing receivables, with an allowance recorded, Related Allowance	655	1,262
Impaired financing receivables, Recorded Investment, Total	2,319	3,869
Impaired financing receivables, Unpaid Principal Balance, Total	2,560	4,094
Impaired financing receivables, Related Allowance, Total	655	1,262
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	5,632	5,983
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	6,191	6,214
Impaired financing receivables, with no related allowance recorded, Related Allowance
Impaired financing receivables, with an allowance recorded, Recorded Investment	1,006	4,192
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	1,123	4,496
Impaired financing receivables, with an allowance recorded, Related Allowance	67	445
Impaired financing receivables, Recorded Investment, Total	6,638	10,175
Impaired financing receivables, Unpaid Principal Balance, Total	7,314	10,710
Impaired financing receivables, Related Allowance, Total	67	445
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	2,115	1,202
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	3,675	2,263
Impaired financing receivables, with no related allowance recorded, Related Allowance
Impaired financing receivables, with an allowance recorded, Recorded Investment	1,403	2,803
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	3,017	4,021
Impaired financing receivables, with an allowance recorded, Related Allowance	896	802
Impaired financing receivables, Recorded Investment, Total	3,518	4,005
Impaired financing receivables, Unpaid Principal Balance, Total	6,692	6,284
Impaired financing receivables, Related Allowance, Total	896	802
Real Estate Construction [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	0	0
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	0	0
Impaired financing receivables, with no related allowance recorded, Related Allowance
Consumer and Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	6	8
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	6	8
Impaired financing receivables, with no related allowance recorded, Related Allowance
Impaired financing receivables, Recorded Investment, Total	6	8
Impaired financing receivables, Unpaid Principal Balance, Total	$ 6	$ 8