Loans - Schedule of Loan Assigned Risk Rating within 12 Months of Balance Sheet Date (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	$ 762,504	$ 771,180
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	424,059	427,715
Commercial Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	338,445	343,465
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	697,370	683,928
Pass [Member] | Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	386,235	388,868
Pass [Member] | Commercial Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	311,135	295,060
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	8,777	22,132
Special Mention [Member] | Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	8,630	8,510
Special Mention [Member] | Commercial Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	147	13,622
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	55,596	64,254
Substandard [Member] | Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	28,874	29,956
Substandard [Member] | Commercial Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	26,722	34,298
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	761	866
Doubtful [Member] | Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	320	381
Doubtful [Member] | Commercial Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	$ 441	$ 485