Allowance for Loan Losses - Credit Exposures by Internally Assigned Grades (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	$ 825,168	$ 741,548
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	774,026	700,407
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	21,756	15,959
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	29,386	25,182
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	128,972	114,186
Commercial and Agriculture [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	112,194	107,903
Commercial and Agriculture [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	1,154	3,446
Commercial and Agriculture [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	5,624	2,837
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	169,600	143,014
Commercial Real Estate Owner Occupied [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	152,878	128,222
Commercial Real Estate Owner Occupied [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	5,232	5,492
Commercial Real Estate Owner Occupied [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	11,490	9,300
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	331,830	308,666
Commercial Real Estate Non Owner Occupied [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	314,420	298,237
Commercial Real Estate Non Owner Occupied [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	13,381	6,305
Commercial Real Estate Non Owner Occupied [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	4,029	4,124
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	120,765	110,341
Residential Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	110,665	100,810
Residential Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	1,970	697
Residential Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	8,130	8,834
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	62,220	59,644
Real Estate Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	62,170	59,584
Real Estate Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	19	19
Real Estate Construction [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	31	41
Consumer and Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	11,781	5,697
Consumer and Other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	11,699	5,651
Consumer and Other [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	$ 82	$ 46