Allowance for Loan Losses - Credit Exposures by Internally Assigned Grades (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	$ 705,327	$ 707,769
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	653,533	660,308
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	20,175	12,190
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	31,619	32,922
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades		2,349
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	107,769	115,875
Commercial and Agriculture [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	98,393	107,923
Commercial and Agriculture [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	3,747	2,038
Commercial and Agriculture [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	5,629	5,914
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	441,263	443,846
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	409,690	415,938
Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	15,509	9,145
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	16,064	18,763
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	104,722	110,210
Residential Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	93,980	98,700
Residential Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	899	986
Residential Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	9,843	8,175
Residential Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades		2,349
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	47,417	35,516
Real Estate Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	47,389	35,495
Real Estate Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	20	21
Real Estate Construction [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	8
Consumer and Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	4,156	2,322
Consumer and Other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	4,081	2,252
Consumer and Other [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposures by internally assigned grades	$ 75	$ 70