Allowance for Loan Losses - Credit Exposures by Internally Assigned Grades (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	$ 700,189	$ 707,769
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	653,868	660,308
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	8,978	12,190
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	35,150	32,922
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	2,193	2,349
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	103,365	115,875
Commercial and Agriculture [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	95,096	107,923
Commercial and Agriculture [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	601	2,038
Commercial and Agriculture [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	7,668	5,914
Commercial and Agriculture [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	440,824	443,846
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	414,126	415,938
Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	7,486	9,145
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	19,212	18,763
Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	106,966	110,210
Residential Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	95,706	98,700
Residential Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	870	986
Residential Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	8,197	8,175
Residential Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	2,193	2,349
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	48,347	35,516
Real Estate Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	48,326	35,495
Real Estate Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	21	21
Real Estate Construction [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades
Real Estate Construction [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	687	2,322
Consumer [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	614	2,252
Consumer [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades
Consumer [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	73	70
Consumer [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades